Part E: Factors Affecting
Maple Health
General
Maple Tree Problems
Extension
State University of New York
H. C. Miller, Professor and Extension Specialist, and S. B. Silverborg, Professor of Forest Botany and
Pathology
College of Environmental Science and Forestry, Syracuse, New York, 13210
New York State Tree Pest Publication F-12
REF# 018
Know Your Maples
Several species of maples are widely used in New York State as street and ornamental trees. The most
common species are (1) black maple (Acer nigrum), (2) striped maple (Acer pennsylvanicum), (3) red
maple (Acer rubrum), (4) silver maple (Acer saccharinum), (5) boxelder (Acer negundo), (7) sugar maple
(Acer saccharum Marsh.) and (8) mountain maple (Acer spicatum). Introduced species are (6) sycamore
maple (Acer pseudoplatanus L.), (9) Norway maple (Acer platanoides L.), and its varieties. Besides being
one of the most desired shade and ornamental trees, the sugar maple is of primary importance in the
production of timber and maple syrup products. See diagram.
Maples, like all other trees, are subject to attack by insects and disease. This publication attempts to
describe these and other serious problems, along with what may be done to remedy them.
Foresters, shade tree specialists, municipal planners, and home owners alike should be able to diagnose
many of the common maple tree problems by using this bulletin.
General Diagnosis Of Maple Tree Problems
Any outward visible evidences of an unhealthy condition in a tree are known as symptoms. There are
certain maple tree troubles which have specific outward symptoms that can usually be diagnosed, while
other problems can be so complex that even trained tree experts cannot always diagnose the cause.
For the shade and ornamental tree owner certain steps are necessary in order to properly evaluate
maple tree problems:
First. Determine whether other maple trees in the locality or in the immediate vicinity show similar
symptoms.
Second. Determine whether the affected trees are growing under favorable conditions in regard to soil,
water, and light.
Third. Determine whether any unusual or special treatments, such as the application of certain types of
fertilizers, insecticides, fungicides, or weed and brush killers were used on or near the trees before the
symptoms appeared.
After investigating the above points, make your next observations by using the following chart. Once
you have established the possible cause, turn to the given pages where detailed descriptions and
suggested treatments are to be found.
Maple Tree Problems at a Glance
Section of tree: Leaves
Problems:
•
Leaves often show the first symptoms. Compare the foliage with other trees of the same
species in the vicinity. Are they of normal size and colour? If not, is this abnormal condition general or
restricted to 1 or 2 branches?
•
Leaves may show a ragged chewed appearance or may be yellowed or blotched.
Possible cause: Feeding activity of sucking or chewing insects.
•
Abnormal leaf appearance, with no insects observed.
Possible cause: Leaf injuries due to fungi are often more difficult to detect. Outlined under
“Specific Problems”.
Section of Tree: Branches and trunk
Problems:
•
Small holes, ridges or tunnels and sawdust.
Possible cause: Insect borers, however, insect damage may appear on trees weakened by other
causes.
•
Branches or twigs with small leaves, wilted leaves, or with no leaves should be examined for
discoloured areas underneath the bark.
Possible cause: Often indicates the presence of wilt-producing fungus.
•
Sunken or dead areas, loose or cracked bark and flow of sap.
Possible cause: If not wilt, chew cankers.
•
Decay in branch crotches, in the trunk or other parts of the tree. Check for fruiting bodies of
fungi or other abnormal growths.
Possible cause: Heart rots.
Section of Tree: Roots
Problems:
•
Trees that have declined over a period of several years.
Possible cause: May be showing the effects of girdling roots.
•
The root system itself may be damaged.
Possible cause: By changes of grade, destructin of roots by curb or road improvements,
construction of pipe lines, low concentrations of leaking illuminating gas, salt compounds used for ice
removal, poor drainage and lack of food nutrients.
•
The sudden death of a tree is often due to destruction of most of the roots.
Possible cause: Lightning, illuminating gas and certain fungi may be among the factors involved.
Specific Problems Caused By Nonparasitic Agencies
Lightning
Large maple trees, or those growing alone in open areas, are most likely to be struck by lightning.
Lightning-struck trees should not be treated until after one to three years have elapsed, because
external symptoms indicating the extent of lightning damage are often slow in appearing. Trees struck
by lightning should be well watered during dry periods, and fertilizers should be applied to keep them in
a vigorous condition. Such trees should receive the attention of a competent tree specialist.
At times maples may have injuries caused by electrical contacts where power lines in close proximity to
branches or limbs are shorted or grounded by the tree itself. Careful pruning will usually eliminate this
problem.
Illuminating Gas Concentrations
At times trees may show a sudden wilting and browning of all the leaves or failure of leaves to expand in
spring. This in turn is followed by the death of many twigs and branches. A characteristic odor is
sometimes apparent near injured trees, particularly in excavated holes.
Trees only slightly injured by gas can usually be saved if the source of the leak is repaired immediately
and the soil aerated. At times gas may permeate soil for some distance from the original source of the
leak.
If trees are killed by gas, additional trees should not be planted on the same site until the leak has been
repaired and the old soil has been removed and replaced with fresh soil, or the site aerated.
Winter or Low Temperature Injury
Injuries to trees caused by low temperatures fall into three separate categories, depending upon the
season:
Autumnal Or Early Fall Frost frequently prevents buds from maturing properly, and unseasonable cold
spells may cause damage to young succulent growth.
Winter Frost affects certain trees, depending upon their location, drainage conditions, and character of
their root system. Affected trees are seldom noted until the following spring or early summer when
wilting and subsequent death occurs on portions of the tree. Root injury is quite common on newly
planted trees and can occur during severe, cold winters with only little snowfall or in soils that have little
or no plant growth. In addition, frost cracks or seams are the result of winter frost (Fig. 1). They are
longitudinal openings on the trunks of trees formed during periods of sudden, severe cold weather.
Frost cracks may often occur on young, vigorous, fastgrowing trees or as a result of fertilization too late
in the growing season. These cracks frequently heal over during the growing season and therefore do
not need special treatment. At times, because of infections such as verticillium wilt (Fig. 6), a slime flux
condition may result on the tree trunk (Fig. 1). However, in cases where natural healing does not occur,
it may be advisable to resort to lip bolting. Details of this may be found in U. S. Department of
Agriculture Farmer's Bulletin No. 1896, titled Care of Damaged Shade Trees.
Figure 1. Diagram
Late Spring Frost. In late spring, when new growth has advanced on trees, a sudden drop in temperature
may cause severe injury. Effects on maples are evidenced by a water-soaked appearance on the leaves,
followed by a blackening, wilting or death of twigs and leaves.
Injuries Due to Drought
Drought injury has become increasingly serious during the past two to three decades. It has resulted
from reduced water supplies available to trees during critical periods, especially during hot, dry
summers or from lowering of water tables due to climatic changes and large-scale building or
development programs.
A direct effect of moisture stress is leaf scorch, an injury produced in the summer during periods of
warm, dry winds. The affected trees are unable to replace the excessive water lost through the leaves.
The edges of the leaves and the area between the veins turn brown. Trees whose root systems have
been damaged or covered with an impervious material, such as asphalt or concrete, are particularly
subject to leaf scorch. Also, reflection from pavement due to position of a tree may cause leaf scorch.
Scorching can be reduced or avoided by measures which will improve the general vigor of the tree: such
measures for trees with a damaged root system include mulching and the maintenance of an even
crown-root ratio by pruning the crown.
Girdling Roots
At times trees are subject to girdling by their own roots which sometimes causes death (Fig. 2). This may
be caused by careless transplanting or may be aggravated by an excess of fertilizers applied near the
trunk. As the small roots close to the trunk increase in diameter and the tree grows larger, the trunk
becomes constricted. If this condition is noticed during the early stages, further damage can be
prevented by severing or removing the guilty root. At times this may not be easy to detect if the root is a
considerable distance below the ground. Usually one side of the tree exhibits symptoms of general
weakening.
Figure 2. Girdling Roots
Root girdling may occur frequently in street trees, particularly those in areas of hard, impervious soil
where good soil was put in at the time of planting. Inability of the roots later to penetrate the
surrounding harder soil causes them to grow only within the filled area and become the girdling type. If
root girdling is in an advanced stage and the tree has been seriously weakened, the services of a
reputable tree company are advised to correct the condition.
Changes of Grade
Raising the grade, i.e., the addition of soil over the existing ground level is called "fill." The extent of
injury from fill varies with the species, age and vigor of the tree, depth of fill, type of fill, drainage, and
other factors. Trees in a weakened condition prior to filling suffer more than healthy ones. The use of a
dry-well or removal of soil to the original level around the trunk will alleviate the situation. If it is not
practicable to remove the fill, then holes 2 to 4 inches in diameter should be augered or punched with a
crowbar to the original ground level every 2 to 3 feet. The outermost holes should coincide with the drip
line of the tree. These holes allow air and water to get to the roots. A mixture of water and fertilizer can
be added in these holes to help the trees recover. These same holes may be filled with crushed stone or
gravel so that they do not create a safety hazard. This type of fill still allows air and water to reach the
roots. As a rule, the amount of fertilizer to be applied is based on the diameter of the trunk in inches at
approximately 4½ feet above the ground. The average amount to apply is about 3 to 5 pounds per inch
of tree diameter using a high nitrogen fertilizer.
Further details are given in the State University College of Environmental Science and Forestry
publication Your Native Shade Tree.
Air Pollution and Other Chemical Injuries
In addition to gas concentrations previously mentioned, other materials can have an adverse effect on
trees.
Various chemicals used as weed and brush killers should be applied only according to the
manufacturer's directions and current pesticide laws. At times, certain conditions such as slope, wind, or
excessive application of chemicals, or other factors, allow accumulations of such chemicals which may
affect the trees adversely for a long period.
Salt compounds used during winter on icy streets and highways can cause decline of maples. These
materials are splashed or washed over curbing by snow-removing equipment or carried by rain water to
root areas. When washed into the ground or when concentrated in certain areas, the chemicals may
themselves, or combined with other factors, cause decline or death of trees.
It has been observed frequently that foliage branching over highways has wilted or turned brown. This
may be due to the high temperature of exhaust gas from passing vehicles with overhead exhaust
systems or the exhausts from all vehicles.
Industrial fumes, especially sulfur dioxide (SO2) and also hydrogen fluoride (HF1), are occasional hazards
to shade trees. However, maples can withstand higher concentrations of gas than many other species.
Sulfur dioxide damage is characterized by a gray-green to straw-colored discoloration between the veins
of the leaves, while the veins themselves remain green. Hydrogen fluoride causes a chlorosis (yellowing)
and death of the leaf margin, in addition to a water-soaked appearance and early leaf fall. Other air
pollutants such as ozone (O3) and peroxy-acetylnitrate (PAN) can become factors inducing chemical
injury in certain areas. Ozone damage is characterized by a metallic flecking or stippling of the upper leaf
surface, while PAN results in a glazing and silvering of the under leaf surface. High concentrations Of 03
and PAN build up in areas where there are many automobiles in use. The exhaust fumes mix in the air
and undergo chemical changes in the presence of sunlight to produce O3 and PAN. Carbon monoxide
(CO) in exhaust fumes can also be damaging to foliage.
Specific Problems Caused By Disease-Producing Organisms
Leaf Diseases
Most leaf diseases are caused by fungi. Several of these produce a spotting effect on leaves. Cold, wet
springs are most favorable for the development of these diseases. Nearly all of them act similarly and
are controlled to some extent by the same methods.
Maple leaves affected with leaf diseases develop dead areas in a variety of patterns, or entire leaves
may be killed. If this happens, a second crop of leaves is usually produced by healthy trees during the
growing season. The prolonged effect over a period of several years will cause harm to the tree.
Anthracnose is a common fungus disease, particularly of silver and sugar maples. It is caused by the
fungus Gloeosporium apocryptum Ell. Ev. The first symptom is the appearance of brown, dead areas
usually near the leaf margins or along one or more of the larger veins, giving a scorched appearance (Fig.
3). In the advanced stages these dead areas coalesce until the entire leaf is dead. Control: Rake and burn
fallen leaves in the fall. In cases where the disease has become troublesome, apply a dormant spray of
lime sulphur followed by bordeaux (8:8:100), fixed copper (50 percent copper) or Ferbam (76 percent).
The first application should be made when the leaves are unfolding and the second when the leaves are
fully grown. If possible, apply spray immediately before a rain.
Figure 3. Anthracnose
Tar Spot is a disease caused by the fungus Rhytisma acerinum (Pers.). It occurs primarily on red and
silver maples. The early stages of this disease are characterized by light yellow-green areas on the
leaves. In the later stages black, raised, tar-like spots 1/8 to 1/2 inch in diameter occur on the upper leaf
surface (Fig. 4). Control: Burn infected leaves in the fall. Spray with 8:8: 100 bordeaux or fixed copper or
Ferbam. The first application should be made when the buds are opening. In severe cases make several
more applications at 2-week intervals.
Figure 4. Tar Spot
Rhytisma punctatum (Pers.) ex Fr. produces numerous small black spots that often do not coalesce. It is
not so frequent as common tar spot.
Phyllosticta Spot is caused by a fungus belonging to the genus Phyllosticta (Fig. 5). It is sometimes
serious, but the symptoms vary on different maple species. On sugar maple the spots commonly have a
narrow purplish border. The affected tissue often falls out with the result that holes are left in the leaf.
On Japanese maple the spots are straw to tan color and usually are small and reddish brown with
narrow to broad purplish borders.
Figure 5. Phyllosticta spot
Spraying with a fungicide, as with other leaf spot problems, should help reduce damage.
Miscellaneous Leaf Spots And Blisters -At times bacterial leaf spot may cause trouble. Other fungi may
cause leaf blisters, gray mold spot, or mildews on various species of maple.
Verticillium Wilt
This is a serious disease, primarily of Norway, silver, and sugar maples and is commonly known as
"maple wilt." It is caused by a soil-inhabiting fungus known as Verticillium sp. Red maple and boxelder
are also susceptible.
The first symptom of this disease is usually a sudden wilting and dying of the leaves on one or several
limbs. Often only one side of the tree is affected, but at times the entire tree may become wilted. The
leaves on affected trees are somewhat smaller than the normal leaves. Trees affected with verticillium
wilt disease often show greenish streaks in the sapwood, particularly of roots (Fig. 6). This is a most
reliable diagnostic characteristic. The fungus that causes this disease lives in the soil, and infection takes
place through the roots. Infection can also occur through wounds on main stems or branches. Control:
Trees showing only slight evidences of wilt, such as one or two affected branches, often can be saved;
removal of the diseased branches and watering aid in tree recovery. Maples showing severe wilt
symptoms cannot be saved. These trees should be cut down and destroyed, and if a new tree is planted
in the same location, it should not be a maple.
Figure 6. Verticillium Wilt
However, if an owner wishes to plant a maple in this same area, possibly removal of a large mass of soil
and replacing with fresh soil or planting of resistant species of trees may improve the situation.
Improving soil fertility by the use of special complete fertilizers containing ammonium sulfate as the
nitrogen source and watering during drought periods may also be an economical approach. No method
is known of treating trees internally for this internal disease. At times some affected trees may recover
without treatment.
Galls or Burls
Globose to subglobose swellings on the trunks or branches of trees are commonly referred to as galls or
burls. The causes of many galls are not definitely known. Some may be caused by injuries, others by
fungi, bacteria, insects, and possibly viruses. On maples, particularly sugar maple, globose galls on the
branches and occasionally the main trunk are caused by a fungus belonging to the genus Phomopsis (Fig.
7). Unless they are abundant, galls of this type do no apparent harm; therefore, no control measures are
necessary.
Figure 7. Phomopsis Gall
Heart Rots
Heart rots in living trees are usually indicated by the presence of external growths, such as mushrooms
or conks (sporophores). In general these do not form until decay has progressed for several years. Heart
rot fungi usually enter the tree through wounds or dead branch stubs.
The fungi commonly producing rots in shade and ornamental maples are as follows:
Fomes applanatus (Pers. ex Fries) Gill. is commonly known as the artist conk. The fungus causes decay in
both the sapwood and heartwood of living maples, particularly sugar maple. The sporophores are shelflike with a grayish, concentrically ridged upper surface and a light-gray under surface (Fig. 8). When
fresh, the lower surface is easily bruised and turns brown when scratched. Because of this, it is
commonly used for sketching by amateur artists. The interior of the conk is dark brown and is separated
into distinct layers by thin strips of brownish fungus tissue.
Figure 8. Fomes Applanatus
Fomes connatus (Weimm.) Gill. is most serious on forest trees and may occur occasionally on shade tree
maples. The characteristic features of this conk are its soft, white, water-soaked texture and the
presence of moss on its upper surface (Fig. 9). This fungus causes a heart rot, principally of hard maple
and red maple, and to a lesser extent other maple species. While this fungus usually causes less loss in
structural strength in a tree than the artist conk, it does present a danger hazard, especially when the
fungus is associated with large wounds.
Figure 9. Fomes connatus
Fomes igniarius (L. ex Fries) Kickx., commonly known as the false tinder fungus, causes extensive heart
rot damage in living trees. The conks are usually hoof-shaped. The upper surface of young conks is
grayish-black to black and becomes rough and cracked with age (Fig. 10). The lower surface is brown and
frequently has a light gray, sterile outer rim.
Figure 10. Fomes igniarius
Fomes fomentarius (Fr.) Kickx., while primarily a destroyer of dead timber, causes decay of both
heartwood and sapwood of living trees occasionally. It is commonly known as the tinder fungus. The
conks are perennial and hoof-shaped (Fig. 11). They have a smooth, gray to brown, concentrically zoned
upper surface and a grayish-brown under surface.
Figure 11. Fomes fomentarius
Steccherinum septentrionale (Fr.) Banker is an important cause of heart rot, particularly in sugar maple.
The soft, annual creamy-white conks occur in bracket-like clusters up to 2 feet or more in length and 3to 6-inches wide. The upper surface is slightly scaly. The under surface contains slender teeth or spines
up to 1/2 inch in length (Fig. 12).
Figure 12. Steccherinum septentrionale
Ustilina vulgaris Tul., known as the coal fungus, causes a basal rot of living trees, entering commonly
through basal wounds or fire scars. Young fruiting structures of the coal fungus are gray on the outside,
black and carbonaceous on the inside. With age they turn black, crustlike, and carbonaceous
throughout.
Polyporus glomeratus Peck occurs most frequently on sugar and red maples. A usually reliable visual
evidence of this heart rot fungus is the presence of swollen woody knobs located at branch nodes.
Frequently, oval to long sunken cankers develop as a result of the fungus growing outward and killing
the sapwood and cambium. Black, sterile, clinker-like fungus material breaks through the face of these
cankers in older infections.
Control Of Heart Rots
Heart rot which is already well-established in shade or ornamental trees presents a difficult control
problem. A good rule to follow in such cases is to remove the tree as a safety precaution. If the tree is
not removed, minor improvements may be made by bolting or cabling. Heart rot losses can be kept at a
minimum if trees are kept free of wounds, and if wounds do occur, they should be treated immediately.
Pruning of dead and dying branches will also reduce heart rot damage.
Canker Diseases
Cankers may be defined as localized diseased areas of the bark usually caused by fungi. The following
three canker diseases occur commonly on maples.
Eutypella Canker. At times maples develop cankers on the trunk in which the bark is killed and a
depression or cankered area becomes evident. It is bordered on its edges by broad, raised rings of callus
tissue (Fig. 13). These cankers are common on hard maple, red maple, and on Norway maple and
occasionally on boxelder.
Figure 13. Eutypella Canker
On shade and ornamental trees the problem is primarily one of weakening of the trunk with possible
wind breakage. Trees with cankers, therefore, create a hazard and should be removed.
Nectria Canker. This canker disease, occurring only occasionally on ornamental maples, is characterized
by sunken areas on the trunk or limbs. The sunken or cankered area usually is concentric or targetshaped in appearance (Fig. 14).
Figure 14. Nectria Canker
The main damage is a weakening of the trunk or larger branches and possible wind breakage at the
canker. As with Eutypella canker, affected trees, especially those in the advanced stages of the disease,
present a hazard and should be removed.
Cytospora Canker. A reliable symptom of this canker disease is a flagging of single branches in otherwise
green crowns of Norway and sugar maples.
Control of canker diseases
It is difficult to control canker diseases that are several years old, due usually to the presence of rot in
the cankered areas. However, young cankers, which are characterized by small, depressed or flattened
areas around wounds or branches, can often be controlled by removing the diseased area. This should
be done by a competent arborist.
Decline Of Maples
This problem has become much more noticeable in recent years. There is still considerable confusion as
to what constitutes "decline of maples". At times "maple blight" has been applied to this condition, but
actually this term applies to a distinct short term disorder caused by insect defoliation, followed by fall
frost which kills buds on the reflush growth-based on research in the Lake States. "Dieback of maples" is
a condition that appears to be associated with a variety of infectious or noninfectious factors, mainly
induced by environmental conditions.
Decline will be characterized by the following symptoms. Usually an abnormal leaf condition, such as
leaf scorch, indicates that a moisture deficiency problem is involved. Often, starting in August, there
may be a premature autumn coloration. As decline continues, there may be death of twigs and branches
of increasing size in the upper crown region; this will be noticeable, as many of the branches fail to leaf
out in the spring. Reduced terminal growth of twigs causes development of foliage in tufts near the twig
ends. Sometimes there may be abnormally large seed crops. In addition, there may be evidences of
injuries, trunk and root rot, and other specific diseases.
Decline in maple woodlots may be partially explained in terms of unfavorable environmental factors.
Heavy over-cutting, with subsequent overexposure of remaining maples in residual stands, probably
contributes the most to this condition. During drought periods, or on shallow soils, this is even more
aggravated and, consequently, becomes more serious. Fluctuation of water table levels-as affecting
dieback-is still being investigated.
Causes of Maple Decline
Each tree will vary in the combination of circumstances and individual factors, because of location and
exposure to the following conditions. Moisture stress will be present almost every summer for trees
growing along roadside and dooryard conditions and can be greatly increased during periods of
prolonged drought. Low soil fertility and compacted soil, in combination with restricted rooting space,
can also be very serious. At times salt compounds used for snow and ice removal probably cause injury.
Severence of roots by construction of pipelines, sidewalks, roads and roadside ditches will cause
additional stresses. This may be followed by root rot, and over a period of time decline will be initiated
in the tree.
Treatment
Obviously the planting of trees away from roadsides or preventing the individual factors or combination
that causes decline is the best preventive. Routine good care in terms of fertilization and pruning, when
necessary, as well as watering during dry periods, will lessen the chances of the problem occurring.
Where trees are already affected, pruning, fertilizing, mulching, and watering are recommended. Where
soil has compacted, it should be loosened to allow aeration.
Many trees already affected, because of changing environmental conditions, are growing in locations
where large shade trees now simply cannot exist. In many municipalities and even on private property,
such trees should be removed and replaced with smaller trees, or none at all, depending upon local
conditions. Municipal authorities should recognize that the useful life span of trees under congested
urban conditions can often be much less than the useful life of that same tree in a lawn or park in the
same area, because of the conditions mentioned above.
Insect And Mite Pests
The insect and mite pests of maple undoubtedly are factors associated at times with general maple
decline. Repeated defoliation will affect the vigor of trees. Normally a healthy tree can stand one or
more defoliations without being seriously affected, but defoliation during a period of drought may have
serious consequences.
It is relatively easy to control most foliage pests with insecticides available from local dealers. Best
control is attained by pesticide application when the pest first starts to feed on new leaves.
Certified applicators, in accordance with state and Federal pesticide laws, can use certain formulations
and combinations for best results. In New York State it is recommended that arborists, municipalities,
and other commercial applicators follow the information in Cornell Recommendations for Pest Control
for Commercial Production and Maintenance of Trees and Shrubs.
In addition, tree pest leaflets on specific pests and control procedures are available from the State
University College of Environmental Science and Forestry. (See list under New York State Publications on
last page.) These leaflets will enable the homeowner to understand the biology and life cycle of specific
pests and the control methods available. These and other publications are available also through the
regional offices of the New York State Department of Environmental Conservation and the Cooperative
Extension Service (County Agents).
Defoliating Insects
Geometridae Or Loopers - Several different species of insects may attack hardwoods-especially maplesat the same time or in quick succession. Insects often involved are the fall cankerworm, spring
cankerworm, Bruce's spanworm, and linden looper (Fig. 15). (See TP leaflet, Cankerworms, F-8 and
Linden Looper, F-22.) Publications are available through cooperating State agencies giving more detailed
information on insect life cycles, as well as control.
Figure 15. Cankerworm
Forest Tent Caterpillar, Malacosoma disstria Hbn. At times these caterpillars are serious defoliators of
sugar maple, but they do not attack red maple. The name is confusing since this species does not make a
tent. The caterpillars make a silken mat on the trunk or branch where they congregate during molting
periods or when at rest. They stay together until nearly full grown.
The hairy caterpillars, when mature, are about 2-inches long and resemble the eastern tent caterpillars.
The head and body are generally pale grayish-blue with fine orange and black lines. There is a row of
keyhole-shaped cream-yellow or white spots along the back (Fig. 16). (See TP leaflet F-9.)
Figure 16. Tent Caterpillar
Green-Striped Mapleworm, Anisota rubicunda (F.) The caterpillar is pale yellowish-green with a large
black head. It has eight longitudinal, lighter yellowish-green lines alternating with seven darker greenalmost black-stripes on the body. Near the head there are two horns, and behind that, two rows of
spines on each side of the body, terminating with four larger spines near the end of the abdomen.
The caterpillars attack several kinds of maple, including boxelder, and may at times cause serious
defoliation. They prefer red and silver maples. When fully grown the caterpillars are 1½ to 2-inches long.
Green Fruitworm, Lithophane antennata (Wlk.). At times, local outbreaks may cause serious defoliation
to maple trees. Normally it causes serious injury to the green fruit of apple, pear, and cherry. The
caterpillar when fully grown is about 1½ inches in length and pale green with a yellowish-green head.
The body has a rather broad white or yellowish- white longitudinal dorsal stripe, and a narrower broken
stripe of the same color on each side of its body. In addition, although the skin is smooth and minutely
dotted with white, the slightly raised tubercles give the caterpillar a roughened appearance.
Saddled Prominent, Heterocampa guttivitta (Wlk.). Although this insect prefers beech, at times there
may be local outbreaks in which sugar maple may be severely defoliated. When fully grown the larva is
about 1½ inches in length and of variable color markings, which in general may be light-green or
yellowish-green with a bluish cast (Fig. 17). There is a saddle-shaped patch on its back, usually of a
reddish-brown or purplish color. The head is large with a broad reddish lateral band. (See TP leaflet F24.)
Figure 17. Saddled Prominent
Gypsy Moth, Porthetria dispar. (L.). The larva of this pest is a general defoliator of forest, shade, and
ornamental trees (Fig. 18). It is now extending its range throughout New York State and adjacent states.
(See TP leaflet F-10.)
Figure 18. Gypsy Moth
The Maple Trumpet Skeletonizer, Epinotia aceriella (Clem.). At times the buildup of this insect may
cause concern to homeowners and municipal officials. Damage seems to be limited to red and sugar
maples. Symptoms first begin to appear in mid to late July as browned skeletonized areas. Infested
leaves are often loosely folded. In general, injury to the tree is more spectacular than serious. By the
time injury really becomes evident, it is too late in the season to cause appreciable damage: the major
portion of the tree's growth is past, and buds have already been formed for the following season. In
general, chemical controls are not necessary under forest conditions. Control measures for ornamentals
should include raking up and destroying infested leaves.
Other Defoliating Insects. At times such insects as the white-marked tussock moth, Hemerocampa
leucostigma (J.E. Smith), maple petiole borer, Caulocampus acericaulis (MacGillivrary), and maple leaf
cutter, Paraclemensia acerifoliella (Fitch) may cause concern.
Sucking Insects
Cottony Maple Scale, Pulvinaria innumerabilis (Rathv.) In the spring the mature female scale is about ¼
inch in length, convex above, and brown in color. When the white cottony egg sack is produced, the
presence of this pest is quite conspicuous, since its appearance resembles that of a white kernel of
popcorn on the twigs of silver maple (Fig. 19). It also occurs on Norway maple, sugar maple, and
boxelder. When unusually abundant, this pest, by sucking the sap, lowers the vitality of the host tree.
Injury may become serious if infestation continues for more than one season.
Figure 19. Cottony Maple Scale
Maple-Leaf Scale, Pulvinaria acericola (W. and R.). This scale resembles the preceding species in general
appearance. It spends its mature stage almost entirely on the leaves of maple and is especially partial to
soft and sugar maples.
Boxelder Bug, Leptocoris trivittatus (Say). This sucking insect is a pest on boxelder trees in some areas of
New York State. The young insects (nymphs) are bright red; the adults are brownish black with three red
stripes on the thorax and red veins on the wings and are about ½ inch long (Fig. 20). These insects feed
on flowers, fruits, foliage, and tender twigs of boxelder. They are especially a nuisance on trees with
female pistillate flowers. At times these insects may be found on ash, maple, and fruit trees. Because
they may build up in large numbers and because of their habit of swarming in autumn, they at times
congregate in large numbers on porches and walks near houses. They may enter houses to hibernate. If
they become a household nuisance, usually sweeping the insects up and burning them is sufficient to
control this pest. Sprays may be used as a control, but if the swarms are of serious concern, check with
your Cooperative Extension Service (County Agents) for latest control measures.
Figure 20. Boxelder Bug (Adult)
Aphids (See TP Leaflet F-19, Forest and Shade Tree Aphids)
Boxelder Aphid, Periphyllus negundinis (Thos.) may at times become abundant enough to warrant
control on the boxelder. The aphids secrete great quantities of honeydew which coats the leaves and
branches with a glossy film. A dark fungus develops in the honeydew, and the tree appears to be
covered with a black sooty coating.
Norway Maple Aphid, Periphyllus lyropictus (Kess.) may cause a similar condition on Norway maples. In
severe infestations the leaves may develop a brownish appearance and become deformed and stunted
and eventually fall off. The aphids, as well as other sucking insects, may be controlled with standard
registered pesticides formulations. Control should usually be attempted before leaves become
damaged or curled.
Borers
The Sugar-Maple Borer, Glycobius speciosus (Say.), a beetle, is one of the worst pests of the sugar
maple, especially on individual trees used as roadside shade trees or ornamentals on private property.
The larva when fully grown is about 2 inches long, robust in appearance, and with brownish mouth
parts. It has tiny legs. Its tunneling causes large dead areas on the main trunk as well as killing or
weakening branches in sugar maple. It is very difficult to control. Whenever burrows of the larvae are
indicated by fresh sawdust, the individual larvae should be cut out and destroyed. (Fig. 21.)
Figure 21. Sugar-Maple Borer (Adult)
Pigeon Tremex, Tremex columba (L.) -The adult is a wasplike insect. It usually attacks diseased and dying
or dead trees. It is fairly common in weakened sugar and silver maples, especially those that have
injured or dead areas. The larvae bore tunnels in the trunks of such trees and help to further
disintegrate the wood. Trees likely to be attacked should be maintained in a vigorous condition, free
from insect pests and diseases. Badly infested trees should be cut down and burned.
The Leopard Moth, Zeuzera pyrina (L.) - The larva of this insect has a brown head, and the body is white
or slightly pinkish in color, with blackish spots. When fully grown the larva is frequently 3 inches in
length. Soft maples are especially susceptible to injury by this insect. Their tunnels weaken the limbs
making them susceptible to breakage. The same measures used to control sugar maple borer are
recommended for this species.
Carpenter Ants, Camponotus pennsylvanicus (DeG.); C. pennsylvanicus ferruginea (Fab.); and C.
noveboracensis (Fitch). Trees of all kinds may be attacked. The ants usually enter through trunk wounds
or the stubs of broken branches where there is dead and decaying wood, and may extend their galleries
from the decayed portion into the sound heartwood. This insect attack adds to the harmful effects of
wood-rotting fungi, both in reducing the physical strength of the tree and in lowering the quality of the
wood.
To prevent carpenter ant attacks in trees, prune carefully and treat bark wounds with suitable dressing.
(See TP leaflet F-3.)
Maple Gall Mites
These gall-producing mites, affecting the leaves of maples, cause peculiar, greenish warts, bumps, or
raised spots that later turn yellow or reddish or black in color (Fig. 22 & 23). The common bladder gall
mites can be controlled by spraying tree trunks and larger limbs during the dormant season, usually
during March and April. (See TP leaflet F-1 1.)
Figure 22. Spindle Galls
Figure 23. Bladder Galls
Miscellaneous Pests
Psocids (Bark Lice) At times very large clusters of brown softbodied winged insects, about ¼ inch long,
may be seen moving in masses on the bark of trees. When disturbed, the whole mass appears to move
at once. These insects, called psocid or bark lice, usually are most abundant about mid August and may
cause concern because they are commonly seen on maple and boxelder. No damage is caused because
they do not feed on the tree but only on decaying organic matter on the ground or on lichens, or bark.
When they occur in large numbers they attract attention and present no real problem other than
nuisance. They may be controlled by insecticidal sprays, but check with your Cooperative Extension
Service (County Agents) for additional information.
General Care Of Maples
Keeping trees in a healthy, vigorous condition is very important in warding off effects of many insects
and disease-producing organisms.
Watering of established trees during dry spells is important. It is even more important to water trees
when they are first planted in a new location. Fertilizing well-established trees is generally a good
practice. Use mulch to conserve water.
Careful pruning of dead and dying limbs also is important.
Tree care should be done by individuals specially trained for the work. Minor tree repair and pruning can
be done by individual home owners. Local tree care companies should be consulted for repair work.
Those companies that can show membership cards in the National Shade Tree Conference or New York
State Arborists Association should give good service.
Persons having questions regarding additional forest and shade tree problems may contact the Tree
Pest Information Service, State University College of Environmental Science and Forestry at Syracuse,
New York. The College will give advice but does not do the actual work of treating trees.
For further information on the insect and mite pests of maples and their control, write to one of the
agencies named below for specific tree pest leaflets:
State University of New York College of Environmental Science and Forestry, Syracuse, New York 13210
New York State College of Agriculture and Life Sciences at Cornell University, Ithaca, New York 14850
New York State Museum & Science Service, New York State Education Department, Albany, New York
12224
Bureau of Forest Insect and Disease Control, New York State Department of Environmental
Conservation, Albany, New York 12201
Useful References
Government And State Publications
Diseases of Shade and Ornamental Maples. Agriculture Research Service U.S.D.A. Agriculture Handbook
No. 211. Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. Dec. 1961.
Common Diseases of Important Shade Trees. By R. Marshall and A. Waterman. U.S.D.A. Farmer's Bul.
1897. Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 1948.
Diseases of Forest and Shade Trees of the U. S. By George H. Hepting. U.S.D.A. Forest Service,
Agriculture Handbook No. 386. Superintendent of Documents, U. S. Government Printing Office,
Washington, D. C. 1971.
Eastern Forest Insects. By Whiteford L. Baker. U.S.D.A. Forest Service Misc. Public. No. 1175.
Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 1972.
Books
Forest Pathology. By J. S. Boyce. McGraw-Hill Book Co., Inc. 3rd Edit. 1961.
The Gardener's Bug Book. By Cynthia. Westcott. Doubleday and Co. Garden City, New York. Revised
1964.
Plant Disease Handbook. By Cynthia Westcott. Van Nostrand Co., New York City. 2nd Ed. 1961.
Tree Maintenance. By Pascal P. Pirone, The Oxford Press. New York City. 3rd Edit. 1959.
Diseases and Pests of Ornamental Plants. By Pascal P. Pirone. The Ronald Press. New York City. 4th Edit.
1970.
Reprints
Comparison of Recent Declines of White Ash, Oaks and Sugar Maple in Northeastern Woodlands. By
Wayne A. Sinclair. The Cornell Plantations, Winter 1964-65 Vol. XX No. 4 pp. 62-67.
Maple Decline (Information Sheet). By David B. Schroeder. Assistant Professor of Plant Pathology,
University of Connecticut, Storrs, Connecticut. Sponsored by Extension Plant Pathologists of the
Northeastern States.
New York State Publications
Additional information on tree care and insects and diseases affecting maple trees can be found in the
following publications, available from the source indicated:
State University of New York College of Environmental Science and Forestry Syracuse. New York 13210
Recipe for Tree Planting. Your Native Shade Tree ($0.15 each), Carpenter Ants (F-3), Cankerworms (F-8),
Tent Caterpillars (F-9), Gypsy Moth (F-10), Maple Gall Mites (F-11), Forest & Shade Tree Aphids (F-19),
Linden Looper (F-22) and Saddled Prominent (F-24)
College of Agriculture and Life Sciences at Cornell University Ithaca, New York 14850
Cornell Recommendations for Pest Control for Commercial Production and Maintenance of Trees and
Shrubs
Verticillium Wilt by W. A. Sinclair and W. T. Johnson, New York State College of Agriculture and Life
Sciences at Cornell University, Cornell Tree Pest Leaflet A-3. 1968.
The Future Of Sugar Maple Vs. Insects And Diseases
Extension
Maple Syrup Digest
James Finley and Thomas Anundson
Vol. 5A, No. 1
This article was partially developed from a presentation by Douglas C. Allen, SUNY, College of
Environmental Science and Forestry.
February 1993
REF# 219
Forest stewardship, biological diversity, and fragmented land ownership will all play a role in the future
of the sugar maple resource. The controversy surrounding proper management of our forests, the effort
to produce diverse forests, and conflicts between neighboring landowners with different goals make the
future of the resource unpredictable. Threats from insect pests such as pear thrips, forest tent
caterpillar, saddled prominent, fall cankerworm, and maple leafcutter, combined with the possible
detrimental effects of environmental pollution and global warming enhance this uncertainty. These
impacts, coupled with the influence of the media, will create a challenge that can only be met through
the application of professional scientific methods and accurate, intensified public education.
Just how important is the sugar maple resource? Consider the following: While New England and New
York produced 890,000 gallons of maple syrup in 1988 (New York Agricultural Statistics Service 1989),
Canada manufactured 3.75 million gallons (Bureau of Statistics of Quebec, 1989). In addition, tens of
millions of dollars are spent annually by "leaf-peepers"—those who enjoy viewing the fall foliage colors.
The total combined value was over one billion dollars—clearly the maple resource is economically
important to both nations.
The income associated with sugar maples contributes to the growth and survival of many rural areas.
Not just for maple syrup and tourism, but sugar maple trees are more valuable now to the timber
industry than every before; the market for sugar maple veneer—a commodity unheard of five years
ago—has reached values as high as $900.00 per thousand board feet.
Sugar maples are the dominant broadleaved tree in the northeastern United States and southeastern
Canada, and can survive in soils that vary greatly in depth, structure, and nutritional quality (Allen 1992).
Previous management practices and varied ecological conditions make the species more susceptible to a
wide range of problems. Still, their presence in most landscapes seems almost assured due to prolific
seed production, tree longevity, and shade tolerance-the ability to survive in low light conditions.
The unexpected explosion of pear thrips populations in 1988 created much concern, mainly because
there was no known control for this pest. Also, the change from forests to farmlands and back to forests
has led to a wide array of diverse management practices that range from establishing natural areas to
clearcutting. Fragmented land ownership patterns and objectives make coordinated aerial control of
defoliators difficult to implement.
We can also expect a significant increase in the damage caused by the sugar maple borer mainly
because it thrives in those low vigor stands created by mismanagement. This insect bores directly into
the tree, creating serious degrade and infection courts for pathogens.
Options used to control defoliators often will be determined by public opinion, not scientific reasoning
or management needs (Allen 1992). The controversy over the use of chemical pesticides may make their
use socially unacceptable or economically impractical. Many landowners hold lands strictly for their
beauty or for recreational purposes and are not concerned about syrup or timber production.
Unfortunately, most landowners can not justify or will not employ silvicultural treatments unless they
remove a product that produces an immediate monetary return to pay for the treatment costs. Many
hardwood stands, therefore, probably will continue to show evidence of crown dieback and instances of
maple decline in regions exposed to drought and/or insect defoliation (Allen 1992).
Other factors that influence the health of sugar maples are:
A.
high-grading—removing all salable logs and leaving genetically inferior stock;
B.
the unpopularity of synthetic organic insecticides to the public;
C.
partial truths regarding forest health issues told by mass media to influence popular opinion;
D.
human population growth and its demands for forest products, and possibly
E.
the effects of global pollution and global warming.
If forest pests gain the "upperhand," it will be because opposing groups can not agree on the best way
to manage the resource. Some feel the stands should be left to nature, others feel the need to produce
better forest products, and still others feel the best solution is to clearcut and start over. Landowners
can help solve these problems by taking advantage of educational opportunities and deciding what is
best for their woodlots. Landowners should consult a professional resource manager when making
management decisions.
Evaluation Of The Condition Of Selected Maple Stands From Northwestern New Brunswick - Research
Report
Research
Maple Syrup Digest
Richard Barry and Edgar Robichaud, École de sciences forestières, Université de Moncton (CUSLM)
Edmundston, N.B. E3V 2S8
Vol. 8A, No. 3
October 1996
REF# 237
Summary
This report presents the results of four years of research activities accomplished within the framework
of the project on the evaluation of the condition of selected maple stands in Northwestern New
Brunswick and the use of fertilization to alleviate maple decline. The four maple stands, two on each of
the two main regolith types: MN and RN stands on the Temiscouata regolith type and BL and CC stands
on the Matapedia/Grog Brook regolith type, were selected in 1990 and their crown conditions were
evaluated during four consecutive years using the North American Maple Project method. At the
beginning of the project, one stand on each regolith type was considered as healthy (RN and GC while
the other (MN and BL) showed signs of moderate decline. The nutrient status at the soil, root, and foliar
level of four maple stands were assessed. The effect of fertilization on the crown conditions and on the
tree nutrient status was evaluated in the MN and BL stands. The project also included the monitoring of
soil temperature and water content in a declining stand (MN) and in a healthy stand (RN). Furthermore,
indirect methods for evaluating foliar area, a potential index of health condition, were investigated.
The crown condition of all four stands deteriorated between 1990 and 1994. The most notable
deterioration occurred in the CC stand between 1990 and 1991, and in the MN and BL stands between
1991 and 1992. In the initially healthy stand, this deterioration was mostly observed through increases
in crown transparency. In the declining stands, the occurrence of dieback increased substantially during
the 1991 season and remained relatively high during the two following seasons. In stands with a high
component of red maple, signs of decline were more frequent, and more severe on this species than on
sugar maple.
Foliar analysis indicated nitrogen deficiency or near deficiency levels in the two declining stands, low
potassium levels in the two declining stands, and low magnesium levels in the four stands. Seven
fertilizer treatments consisting of nitrogen, calcium, magnesium, and potassium applied individually or
in combinations were applied to 40 declining trees in the MN and BL stands.
The trees selected for the fertilization trial generally improved their crown conditions. However, the
effect of this improvement was not linked to the fertilization effect since improvements of the same
order were also observed on the control trees. In the BL stand, fertilization seems to have accelerated
the improvement of crown transparency ratings when compared with the control. In that stand, all
treatments appeared to have reduced the proportion of trees showing transparency levels above 15%
one or two seasons more quickly than for the control. In both MN and BL stands, the reduction in the
number of trees showing transparency ratings above 15% dropped sharply during the years following
fertilization, except for the control group where it increased slightly during the second season after
fertilization. However, comparisons of the average difference between the levels of symptoms observed
during the year before fertilization (1990) and the years following fertilization (1991-92-93) indicated
only very few significant changes attributable to treatments. When compared to the control trees, the
Mg treatment resulted in a slight but significant increase in crown dieback in the MN stand, and the
NCaMgK treatment resulted in a slight decrease in the transparency level in the BL stand.
Analysis of foliar nutrient concentrations in response to fertilization treatments confirmed the low
nitrogen status observed at both MN and BL sites. Significant increases in both foliar N concentration
and content were observed in all trees which were fertilized with nitrogen. However, only treatments
combining N with K, and with the other base cations (NCaMgK) resulted in an increase in N
concentration during the two seasons following treatment, indicating that these elements are also
deficient in this stand. However, because most of the treatments did not increase the concentration in
base cations during the first season, some desequilibria in the N:base cations (Ca, Mg, K) ratios may have
been induced by the treatments.
In the BL stand, treatments NMg, CaMgK, and NCaMgK resulted in a significant increase in foliar calcium
concentration during the first season following fertilization, and foliar magnesium concentrations were
also increased by treatment NCaMgK. Some desequilibria, expressed by the N:base cations ratios, were
also induced by the application of these treatments.
During the summer and early fall of 1991, the movement of fertilizers through the soil was monitored
using tension lysimeters and ion exchange resin bags. The sampling with tension lysimeters was
continued during summer 1992. Although it was not possible to assess the net loss of added nutrients by
leaching under the rooting zone, both methods indicated significant losses of ammonium, nitrate and
base cations during the first season following fertilization, important losses of base cations during the
second year, mostly calcium and magnesium, and lower losses, but still significant during the third
season.
Fine root biomass and nutrient content of the two stands on the Temiscouata regolith type (MN and RN)
were evaluated. Fine root biomass was higher in the declining site (MN), reflecting the lower fertility of
the site and the requirement for a larger root system to access the required nutrients. Roots were also
concentrated nearer to the surface in the MN site, possibly rendering them more susceptible to
environmental extremes (i.e. frost, desiccation). Fine root nutrient concentrations generally reflected
the foliar nutrient status with lower levels of most major nutrients (except Ca) in the MN site. In
contrast, levels of Al were higher in the MN site.
Those root parameters were also evaluated in the MN stand during the second season after fertilization
(1992) in order to compare the effect of the treatment on the nutrient status of the root system.
Soil temperatures measured in the rooting zone were generally higher in the declining MN stand than in
the healthy RN stand. However, differences between the two stands were always small, being less than
one degree C during the three years of observation. Soil frost, a factor proposed as an inciting factor in
hardwood decline, was observed in both stands frequently during the three winter seasons at 5 cm,
sporadically at 15 cm, and never at 35 cm.
Soil water content measured in both stands were generally very low during the growing season,
sometimes reaching levels associated with values of permanent wilting points, notably during early
summer 1991 and 1993. The effect of this drought on the progression of decline symptoms in these
stands is difficult to assess since these low soil moisture values were observed in both declining and
healthy stands.
The method used for the evaluation of the health status of the tree is based on a rating of decline
symptoms determined by a visual appreciation of some crown characteristics. In order to identify a
more objective method to make this evaluation, the potential usefulness of different tree
measurements (diameter at breast high and at the base of live crown, crown volume, sapwood crosssectional area, annual ring area) to predict the foliar area was assessed. Between 10 and 15 trees were
sampled in four healthy maple stands and in one declining maple stand. It was found that the use of a
linear regression equation combining the cross-sectional sapwood area at breast high, the annual ring
area of the former growing season measured at breast high, and the crown volume provided reasonably
good predictions (r2 > 0.91) of the foliar area. However, the operational applicability of this method for
the evaluation of the effects of fertilization on crown conditions remains questionable.
Fungi, Pear Thrips And Ants
Research
Maple Syrup Digest
Michael Brownbridge, Jim Boone, Margaret Skinner & Bruce L. Parker, Entomology Research Lab
University of Vermont
Vol. 7A, No. 2
June 1995
REF# 234
While pear thrips populations and subsequent levels of maple damage have fluctuated since the major
outbreak of 1988, it has become very clear that pear thrips is not a temporary pest that will simply
disappear, but poses a real threat to the long-term health of sugar maple forests throughout the
Northeast. Management of this pest is complicated by its cryptic habits and its biology, and conventional
chemical controls are not a viable, or desirable, option. Use of biological controls offer great potential
for management of pear thrips, and studies at the University of Vermont, Entomology Research Lab,
have focused on the development of native species of insect-killing fungi for use in a thrips suppression
program. These commonly occurring insect diseases are capable of killing a variety of pest species, and
already contribute to the natural regulation of this tiny insect. The control strategies we envision would,
in a sense, help alter the balance of nature in our favor by augmenting populations of these beneficial
microbes in maple forest soil.
Two types of fungi are being used in our on-going trials, Verticillium lecanii and Beauveria bassiana, both
originally isolated form infected insects collected in a Vermont maple stand. We chose to apply fungi to
the forest floor, targeting thrips entering the soil to pupate and overwinter. The trials were conducted to
address two basic issues: 1. how effective are the fungi against pear thrips under field conditions; and 2.
can we enhance soil populations of these fungi and for how long. Data obtained from these field tests
will indicate the feasibility of using the fungi in a control program, and whether we can establish higher
levels of fungi in the soil to potentially provide a long-term source of infection for pear thrips.
Results of trials done in 1994 show that, for both fungi, the number of infected larvae recovered from
samples taken in treated plots was significantly greater than the number recovered from control plot
samples. In addition, we were able to detect enhanced levels of inoculum in the soil for over 3 mo. in
soil samples collected from plots seeded with Beauveria in 1993, we found that pathogen levels were
still greater than 40 times higher than the controls more than a year after the treatment was applied.
Thus, on the basis of the results obtained, we appear to be able to obtain reasonable control of thrips
with the selected fungi, and to positively influence the level of inoculum in forest soil. In trials scheduled
for this year, we aim to modify our treatment regime to attain even better levels of control.
The fungi show great promise for pear thrips management, but what of the broader host spectrum of
these agents? If the fungi are to be used in a sugarbush, it is essential that their impact on key nontarget beneficial organisms is understood. Therefore, we have been conducting a series of tests on the
ant species Camponotus pennsylvanicus. This insect is commonly found in maple forests where it is an
important general predator, feeding on a variety of defoliating insects, and plays a major role in the
decomposition cycle. Through its foraging activity it would possibly be exposed to fungi applied to the
forest floor for thrips control.
In lab trails, ants were first directly treated with formulated and non-formulated fungi, and then held
under conditions to promote infection. Sure enough, under these conditions, the fungal isolates tested
were very pathogenic. For both Beauveria treatments, close to 100% of the test insects were killed
within 14 d, compared with only 17% mortality in the controls.
To more closely simulate natural conditions, the pathogenicity of formulated B. bassiana to ants was
tested in soil. First, sterile maple soil was used to eliminate potential fungal competitors and
antagonists. Subsequent trials were done with non-sterile soil. In the sterile soil, 25% of the ants died
after 7 d, rising to 85% by day 14, compared with less than 5% mortality in the controls at both time
intervals. In nonsterile soil, however, no ants had died by day 7, and around 40% of the exposed
population died after 14 d, significantly lower than the mortality levels obtained on the sterile soil. This
year, we will evaluate effects under true field conditions, caging ants in plots treated with fungi to
control pear thrips. While lab results suggest that the ants are susceptible to the fungi being used in our
trials, these tests were conducted under conditions heavily biased to enhance development of a fungal
infection. The dose levels used were purposely, but unnaturally, high, and the ants were a “captive”
audience within the treatment arena. Holding the insects under artificial conditions also provides an
additional source of stress that would pre-dispose the ants to infection. In a forest, this would not be the
case, and a variety of other factors would influence the activity of the pathogens. As such, effects seen
in the lab are unlikely to be repeated in the field. The potential impact of these microbes on the
environment and other non-target beneficials will unquestionably be minimal, particularly when
compared with any of the conventional chemical insecticides contemplated for pear thrips
management. We must remember, these fungi are already working in maple forests, we are simply
trying to make them work better to provide an ecologically safe solution to a perennial pest problem.
Diagnosing Injury to Eastern Forest Trees — A manual for identifying damage caused by air pollution,
pathogens, insects, and abiotic
stresses
Extension
Pennsylvania State University, College of Agriculture
Contributing Authors: Samuel A. Alexander, Virginia Polytechnic Institute and State University,
Blacksburg, VA, Dale R. Bergdahl, University of Vermont, Burlington, VT, E. Alan Cameron, The
Pennsylvania State University, University Park, PA, Boris I. Chevone, Virginia Polytechnic Institute and
State University, Blacksburg, VA, Donald D. Davis, The Pennsylvania State University, University Park, PA,
Alan R. Gotlieb, University of Vermont, Burlington, VT, Fred P. Hain, North Carolina State University,
Raleigh, NC, Roy L. Hedden, Clemson University, Clemson, SC, Craig R. Hibben, Brooklyn Botanic Garden
Research Center, Ossining, NY, David R. Houston, USDA Forest Service, Northeast Station, Hamden, CT,
Lance W. Kress, Argonne National Laboratory, Argonne, IL, John A. Laurence, Boyce Thompson
Institute, Ithaca, NY, Robert Lewis, Jr., USDA Forest Service, Northeast Station, Broomall, PA, William
Merrill, The Pennsylvania State University, University Park, PA, Paul A. Mistretta, USDA Forest Service,
Southern Station, Pineville, LA, R. Marcel Reeves, University of New Hampshire, Durham, NH, John M.
Skelly, The Pennsylvania State University, University Park, PA, Stanley R. Swier, University of New
Hampshire, Durham, NH, Frank H. Tainter, Clemson University, Clemson, SC, Philip M. Wargo, USDA
Forest Service, Northeast Station, Hamden CT.
Editors: John M. Skelly, Department of Plant Pathology, Donald D. Davis, Department of Plant
Pathology, William Merrill, Department of Plant Pathology, E. Alan Cameron, Department of
Entomology, The Pennsylvania State University, University Park, PA, H. Daniel Brown, USDA Forest
Service, Southern Region, Atlanta, GA, David B. Drummond, USDA Forest Service, Southern Region,
Pineville, LA, Leon S. Dochinger, USDA Forest Service, Northeast Station, Delaware, OH,
1987
REF# 395
Foreword
The Forest Response Program (FRP) is evaluating the responses of forests to acidic deposition and
associated pollutants. The program is sponsored by the National Acid Precipitation Assessment Program
(NAPAP) and funded by the U.S. Environmental Protection Agency, the USDA Forest Service, and the
National Council for the Paper Industry for Air and Stream Improvement. Scientists working in this
program realize that proper identification of damage symptoms on forest trees and stands is crucial.
Thus, the Forest Response Program's National Vegetation Survey has supported the development of
both pictorial and descriptive information on atmospheric pollutant damage to trees in the context of
other known damaging agents whose visible symptoms may be confused with those caused by
pollutants. We are pleased to sponsor this publication summarizing our current knowledge about the
visible symptoms of air pollutantinduced injury. We hope this document meets user needs.
Ann E. Carey National Program Manager
Joseph E. Barnard Manager, National Vegetation Survey
This research was supported by funds provided by the National Vegetation Survey within the joint U.S.
Environmental Protection Agency-USDA Forest Service Forest Response Program. The Forest Response
Program is part of the National Acid Precipitation Assessment Program. This paper has not been subject
to EPA or Forest Service policy review and should not be construed to represent the policies of either
agency.
Preface
Awareness of and concern for air pollution injury to forest vegetation have increased over the past
several decades. Our knowledge of expected air pollutant doses and their injurious effects on the foliage
of forest trees and associated species has increased concurrently. Until 1985, however, critical,
extensive field evaluation of air pollutant-induced injury to forest species had not been considered,
either regionally or nationally.
In early 1985, under the auspices of the National Acid Precipitation Assessment Program, the U.S.
Environmental Protection Agency and the U.S. Department of Agriculture Forest Service formally agreed
to carry out a coordinated program of research on the effects of acid rain and its associated pollutants.
Task Group F (Terrestrial Effects) of this effort includes a Forest Response Program consisting of six
research cooperatives with specific responsibilities and appropriate deposition monitoring support to
investigate air pollutant effects on various major timber types. The National Vegetation Survey, one of
these cooperatives, has a major role in answering questions on the baseline and current condition of our
nation's forest resources. Knowledge of the natural variation in forest resources is also needed in order
to better understand potential atmospheric deposition effects and impacts. The USDA Forest Service
chartered the National Vegetation Survey to accomplish a systematic, comprehensive inventory and
analysis of those forests in the eastern United States that are exposed to air pollutants.
The National Vegetation Survey will develop and apply appropriate statistical procedures to the
identification of variation in condition parameters for specified forests, stands, or tree species. At a
minimum, these evaluations must have the potential to segregate natural variation from a second,
unexplained category, which may be correlated with spatial patterns of various atmospheric pollutants.
The spatial correlation step will require the recognition of spatial and/or temporal patterns in the
existing condition of our forests.
Purpose
The purpose of this manual is to assist members of the National Vegetation Survey in recognizing air
pollutant-induced injury and in identifying disease and insect damage that may be confused with air
pollutant-induced injury to forest vegetation in the eastern United States. Ozone, sulfur dioxide, and, to
a limited geographic extent, hydrogen fluoride, are all pollutants of concern in relation to forest
vegetation; detailed descriptions of the injuries caused by these pollutants are presented herein.
A second section of this manual has been prepared to assist the survey in recognizing other major
diseases, insects, and abiotic stresses that may be found at the survey plots. These disorders were
chosen because their symptoms may be similar to those caused by air pollutants. Basic information and
the most typical symptoms for each of these causes of stress are also presented photographically.
It is important that both sections of this manual be consulted thoroughly to relate field symptoms
accurately to the most likely cause of the observed symptoms. In all cases, the presence of biotic
pathogens, insects, and other indicators of plant stress should be investigated and recorded.
Finally, this manual has been designed to minimize errors in identifying the actual causes of symptoms
evident in each plot. All potential causes must first be eliminated before the injury is ascribed to an
unknown cause.
Survey crews should follow carefully the prescribed sampling and/or searching techniques for causal
agents as outlined in this manual. Individuals should also consult other references to identify disease
and insect problems that may not be covered in this manual.
Air Pollutants
Many gaseous pollutants exist in our atmosphere. Under widely variable forest conditions, however,
only three major pollutants have been demonstrated to cause significant foliar injury to forest trees:
ozone, sulfur dioxide, and fluoride. Recently, sulfates and nitrates-acid depositions have also attracted
interest, but direct foliar injury to vegetation has been observed under natural conditions only where
the vegetation is very close to the pollutant sources, i.e., in a direct plume dispersion path.
Other minor pollutants, such as hydrogen chloride, bromine, particulates, and nitrogen oxides, have
been shown to have local effects and may be of local importance. Survey crews must be aware of
potential sources of these pollutants if they occur in areas close to established plots. If such sources are
suspected of being involved in an observed symptom pattern, further checking should be done by
experts.
Several available references show color illustrations of injury symptoms caused by these and other
pollutants. If any one of these pollutants is suspected of causing injury observed during the survey,
these references should be consulted.
Vegetation Surveys For Air Pollution
Surveying and identifying air pollutant impacts to forest ecosystems can be a complex and intensive
task, depending upon the plant processes affected. Visible foliar injury resulting from exposure to air
pollution commonly occurs on sensitive forest species.
Symptoms of injury to sensitive species can be used to effectively survey the extent and severity of
pollution injury to forest trees. The following is a discussion of survey techniques using foliar
symptornatology. Refer to Skelly et al. (1979) for a more in-depth discussion of this subject.
Types of Field Surveys
The design of a field survey is generally dictated by the type of source from which the pollutant
originates. Five different types of sources have been designated: single-event point sources (chemical
spills); line sources (heavily utilized highways); continuous point sources (smokestacks); area sources
(large urban communities); and regional sources adjoining urban or industrial areas.
Phytotoxic air pollutants can be characterized as to source type. Sulfur dioxide, hydrogen fluoride,
coarse particulates, and most heavy metals except lead are emitted primarily from point sources. The
principal source of atmospheric lead is the combustion of leaded gasoline; high concentrations of this
metal can be found in vegetation adjacent to major highways. Ozone, acid sulfate aerosols, peroxyacetyl
nitrate, oxides of nitrogen, and nitric acid vapor are considered to originate from area or regional
sources, since most of these pollutants are formed secondarily by chemical reactions in the atmosphere.
Acid sulfates and nitrates are currently being studied for possible direct and indirect effects.
Typical patterns of pollutant concentration are associated with a specific source type. A well defined
concentration gradient can exist in the prevailing downwind direction from a point source. Vegetation in
this downwind region is often exposed to the highest pollutant doses, and a gradient of foliar injury may
occur in conjunction with this concentration gradient. Injury is most severe near the pollution source
and gradually diminishes in severity as the distance from the source increases. By contrast,
concentrations of atmospheric pollutants resulting from area or regional sources are fairly uniform over
large geographic areas, especially where terrain is relatively flat across extensive land areas. Foliar
symptoms may be more intense directly downwind of urban or industrial sites but may not be limited to
these regions.
A variety of survey designs have been used successfully to determine the extent and severity of air
pollution effects on terrestrial vegetation. For point sources, radial transects are typically established
from the center of the source. These transects are usually longer in the downwind direction and shorter
in the upwind direction to delineate the impact zone most efficiently. Survey plots are located along
these transects at geometric or logarithmic intervals and at distances from the source sufficient to
encompass areas containing nonaffected vegetation. Survey designs for area or regional sources
typically consist of some type of grid system. The grid spacing is determined by the size of the region to
be surveyed and by the available resources. Plot sites are tentatively selected along grid lines on county,
state, and regional maps. In practice, plot locations are determined by accessibility and presence of
selected species. Grid density can be varied to sample more intensively the vegetation surrounding
urban and industrial pollution sources.
Plot Selection Considerations
Numerous physical factors can affect pollutant transport and dispersion and alter plant sensitivity to
pollutant exposure. The effects of these factors on ambient-pollutant concentrations depend upon the
type of emission source.
Regional scale meteorology and topography modify atmospheric conditions, thereby influencing
pollutant concentrations regionally. During the summer months, large, slow-moving, high-pressure
systems reduce surface air mixing and limit pollutant dispersion. Pollutant episodes may occur during
these weather patterns, and high concentrations of regionally generated pollutants such as ozone and
acid sulfates may persist for several hours daily until the high-pressure system passes.
In contrast, the direction of prevailing surface winds is a primary factor influencing pollutant transport
from local point sources. In flat to gently rolling terrain, sources of pollution may dominate patterns of
pollutant concentration on a local scale. Mountainous terrain, especially the ridge-and-valley
topography typical of the central and southern Appalachian Mountains, substantially affects surface
wind direction, resulting in air flow parallel to major terrain features. Pollutant dispersion is complex in
these regions. Inversions are common in deep, steep-walled valleys, and high concentrations of
pollutants can be expected near sources within these valleys.
Environmental and soil conditions affect the growth and physiological status of a plant and modify its
sensitivity to air pollutant-caused stress. The availability of soil moisture influences plant response to
gaseous air contaminants. In drought situations, plant stomata will close, limiting foliar gas exchange
and reducing both the entry of pollutants into leaves and subsequent cell damage.
Soil nutrient status also can affect how a plant responds to air pollutants. Vegetation growing with
limited essential nutrients is usually more sensitive to gaseous pollutants, such as ozone, than is
vegetation growing with an adequate nutrient supply. Where soil sulfur is limited, however, low
concentrations of sulfur dioxide or sulfate in wet deposition may enhance plant growth by increasing
sulfur availability.
Species, Specimen Selection, and Timing Considerations
Air pollutants often induce a characteristic type of foliar symptom on plant species. In selecting species
for a field survey, it is helpful to know what pollutants might be present at phytotoxic concentrations in
the survey area. Those species that exhibit the highest sensitivity to a particular pollutant should be
chosen for surveying. Ideally, two or three commonly occurring pollutant-sensitive species should be
available in the survey area for a comprehensive assessment of air pollution injury.
The accessibility of foliar material for visual inspection should be considered in specimen selection. This
approach limits size of specimens to those trees with foliage that can be sampled by hand or by some
device such as a pole pruner. Since the canopy of a forest stand intercepts atmospheric pollutants, the
concentration of pollutants decreases from the top of the canopy to the forest floor.
Therefore, specimen trees selected for surveying should be dominant or co-dominant or on the edge of
a stand where the foliage is openly exposed to atmospheric depositions.
The best time of year to conduct a vegetation survey in the eastern United States, particularly when
ozone is the pollutant of interest, is in late summer, since the cumulative effects of ozone over a
growing season may not appear until that time. Once fall coloration has begun, the foliar effects of air
pollution are difficult to assess accurately.
Ozone
Ozone (O3) is the most widespread air pollutant in the United States, causing more plant damage than
any other. Injury has been observed throughout the United States in both rural and urban areas and on
numerous plant species.
Sources
Ozone is known as a secondary pollutant and is formed in the air by the action of sunlight on
hydrocarbons and oxides of nitrogen, the primary pollutants. Ozone is also generated naturally by
electrical discharge during thunderstorms and by the action of sunlight on oxygen in the upper
atmosphere. These natural sources do not contribute significantly to the ground-level concentrations Of
O3, with the possible exception of those found at higher elevation sites. High O3 concentrations usually
occur many miles from the sources of the primary pollutant emissions; such concentrations can injure
and retard the growth of many plant species.
Symptoms
The visible symptoms resulting from O3 exposure are generally recognized as either acute or chronic
responses. Acute injury normally involves the death of cells and develops within a few hours or days
following exposure. Expressed as stippling, flecking, bleaching, and bifacial necrosis, acute injury is
usually associated with exposure to high O3 concentrations. Chronic injury typically develops more
slowly, within days or weeks following exposure, and may be manifested as chlorosis, pigmentation
(stippling), premature senescence, and necrosis. Chronic injury usually appears in response to long-term,
low-concentration exposure. Both symptom types, however, may occur in response to either high or low
concentration exposures, depending on the environmental conditions and the genetic and physiological
condition of the plant. Both types of symptoms, particularly those of chronic injury, may be confused
with symptoms of other conditions, such as normal senescence, nutritional disorders, other
environmental stresses, biotic pathogens, or insect infestation.
Broadleaf species: Ozone causes several general symptoms on broadleaf species in the field, the most
common of which is stipple, or pigmentation.
The upper leaf surface of plants may have a tan, red, brown, purple, or black coloration that appears
uniformly over the leaf surface, is restricted to certain areas of the leaf, or appears as discrete, dot-like
lesions (Figures 1- 8). The upper leaf surface may be uninjured, with only the underlying palisade cells
affected. Veins and veinlets are usually not involved, and veinlets often bound the injured areas,
producing angular sections of affected tissue. Sometimes stippling is best observed by holding the leaf
toward the sun (Figure 9); the symptom is often more intense on leaves exposed to direct light. In the
absence of further stress, the stippling may fade and become difficult to discern one to four weeks
following exposure.
Figure 1. Dark pigmented stipple on upper surface of green ash leaflets exposed to O3
Figure 2. Dark pigmented stipple on upper surface and general chlorosis of yellow-poplar leaves exposed
to O3
Figure 3. Dark pigmented stipple on upper surface of sweetgum leaves exposed to O3. This can become
almost solid purple or maroon, similar to normal fall coloration.
Figure 4. Dark pigmented stipple and slight chlorosis on upper surface of leaves on a black cherry
seedling exposed to O3
Figure 5. Dark pigmented stipple on sassafras leaves exposed to O3
Figure 6. Dark pigmented stipple and senescence on a poplar leaf exposed to O3.
Figure 7. Very mild stipple on upper leaf surface of sycamore seedling exposed to O3.
Figure 8. Dark purple stipple on upper leaf surface of wild grapevine exposed to O3.
Figure 9. Dark pigmented stipple on ash leaflet; observed when symptomatic leaflet is held up to the
light.
Stippling has been described as the classic symptom of O3 injury on broadleaf trees. The coloration of
stippling is usually characteristic for a species but can vary with environmental or physiological
conditions. The youngest fully expanded leaves are normally the most sensitive, although all but the
very youngest leaves may be affected. On young leaves, symptoms tend to develop at the tips; on older
leaves, toward the base. The entire surface of older leaves may exhibit symptoms when exposed to
ozone periodically during growth. On plants with pinnately compound leaves, such as ash hickory, and
tree-of-heaven, only some leaflets at certain positions along the petiole may be affected. Because
stippling is a photosensitive response, overlapping leaflets or leaves may create a sharp line of
demarcation between injured and uninjured, or shaded, tissue (Figure 10).
Figure 10. Dark pigmented stipple on upper leaf surface of hickory exposed to O3. Note protected area
of leaf overlap.
Chlorosis, or loss of chlorophyll, may occur as a generalized condition similar to senescence, in discrete
patches called mottle, or in patterns similar to stippling. Chlorosis is often more prevalent on the upper
leaf surface of species that have palisade cells (Figure 11). Fleck injury is characterized by small, discrete
areas of dead cells- usually palisade and sometimes associated epidermal tissues-leading to the
formation of irregular lesions on only one leaf surface, usually the upper (Figure 12). The lesions are
often bleached (unpigmented) but can be colored as in stippling, and the affected areas may be slightly
sunken.
Figure 11. American sycamore seedling exposed to O3, showing tan stippling, that gives an overall
chlorotic and bronzed appearance to the upper leaf surface.
Figure 12. Fleck on poplar leaf exposed to O3.
Bifacial necrosis results when the tissues connecting the upper and lower leaf surfaces are killed. The
tissue coloration ranges from white to red-orange to black and is often characteristic of a specific tree
species. Small veins are usually included in the necrotic tissue, but larger veins often remain alive. The
area of dead cells collapses, and the upper and lower leaf surfaces draw together to form a papery
lesion.
Although stippling is usually interveinal, extensive injury can also affect many of the veins themselves, as
in generalized chlorosis. In some species, especially sycamore, stippling tends to appear adjacent to the
larger veins. In bifacial necrosis, the leaf margins are sometimes the most severely injured. Prolonged
low dose exposures may cause coalescence of chlorotic tissues, light stippling, and/or production of a
bronzed appearance. Premature defoliation may follow.
Conifer species: On conifer species, the two most common needle symptoms are chlorotic mottle and
tipburn. In general, mottle of young and older needles is induced by low dose exposures, while tipburn
of young needles is induced by high dose exposures. There is, however, considerable overlap depending
on species, within- species variation, timing of exposures, and environmental conditions. Chlorotic
mottle develops as small patches of yellow tissue surrounded by apparently healthy tissue (Figures 1315). The tissue, especially in young needles, may also become tan. Necrotic tips result from tip dieback
or from necrotic banding, which may develop when medium-aged tissue along an individual needle is
most sensitive (Figure 16). Eventually, the rest of the tip portion of the needle may also die, producing
necrotic tips with a reddish brown coloration that fades with age. Toward the end of the growing
season, these necrotic tips may break off, making affected needles appear much shorter. The tipburn
symptom, especially in white pine, usually affects all needles in a fascicle equally.
Figure 13. Chlorotic mottle on needles of eastern white pine exposed to O3.
Figure 14. Chlorotic mottle, developed over a period of days or weeks, on older needles of eastern white
pine exposed to O3.
Figure 15. Close-up of chlorotic mottle on Virginia pine exposed to O3.
Figure 16. Tipburn on eastern white pine exposed to O3. Length of necrotic tips may indicate pollutant
concentration. Note evenness of symptoms on all needles in one fascicle
Young, rapidly growing needles that are directly exposed to sunlight are the most sensitive, but older
needles can exhibit mottle and premature senescence as a result of prolonged low dose exposures. As is
true of broadleaf species, symptoms on plants within a single conifer species can vary considerably.
Ozone-sensitive plants exhibit premature defoliation of older needles, general needle chlorosis, and
needle shortening. Such trees, known as chlorotic dwarfs, have thin chlorotic crowns and tufted foliage
(Figure 17).
Figure 17. Eastern white pine clones showing variable sensitivity to O3 in trees of same age. Sensitive
clone in foreground (chlorotic dwarf) and tolerant clone in background.
Grass and herbaceous species: On most grass species, tissue injury can be prominent on either leaf
surface. However, as in the broadleaf and coniferous species, the leaf surface exposed to direct sunlight
generally exhibits greater injury. Symptoms are often most pronounced at points of bending of leaves.
Most of the grass species are less sensitive to ozone than are broadleaf and coniferous species like black
cherry, yellowpoplar, and white pine.
Bioindicator species: Some particularly sensitive tree species, including white ash and clonal lines of
eastern white pine, have been used as bioindicators of ozone air pollution. Black cherry appears to be a
good indicator of ozone. Other forest species that may serve as bioindicators of ozone pollution are
blackberry, milkweed, and poison-ivy. Blackberry (Figure 18) and poison-ivy exhibit a dark purple-red
stippling of the upper leaf surface that often coalesces over most of the leaf surface. The symptom on
milkweed (Figure 19) is similar to that on blackberry, except that the coloration is purple-black.
Milkweed has been reported as a common bioindicator of ozone.
Figure 18. Purple-red coloration on upper leaf surface of blackberry, one of the first species to exhibit
O3 Symptoms.
Figure 19. Dark stipple on upper leaf surface of milkweed and general chlorosis suggestive of senescence
following exposure to O3.
Concerns in Diagnosis
Plants often respond to different stresses in a similar fashion. Several incitants other than air pollutants
are known to cause symptoms similar to those induced by O3. On broadleaf plants, leafhoppers and
spider mites often cause a chlorotic stippling that may become pigmented with time. Close examination
usually reveals evidence of the insect pest; these insects injure both the lower and upper leaf surfaces.
Sunburn, sunscald, or severe lateseason droughts may cause bronzing or general purpling of the upper
leaf surface. Viruses can also induce chlorotic mottling. Marginal necrosis produced by O3 on an
expanding leaf may cause leaf crinkling and be misdiagnosed as a virus. Herbicide injury may also be
confused with air pollution injury.
Individual plants within the same species may differ in pollution sensitivity. Genetic and microclimatic
differences may produce apparently sensitive and tolerant individuals side by side, but multiple species
are often found to exhibit injury at the same time. Symptoms generally appear over a whole tree rather
than a single stem or branch and may be more severe in plants growing on open sites. Leaf age,
especially in broadleaf species, is an important factor in conditioning sensitivity; injury to very young
tissue can also be caused by agents such as frost or herbicides. An appreciation of species sensitivity,
classic symptom patterns, and other disease and insect-induced problems is important for accurate
diagnosis.
Sulfur Dioxide
Sulfur dioxide (SO2), a wellknown air pollutant that is toxic to vegetation, has been recognized for
causing damage to plants since the late 1800s. More studies have been conducted on the effects of
sulfur dioxide than on any other pollutant.
Sources
Sulfur dioxide (SO2) is emitted into the atmosphere when materials containing sulfur are burned.
Industrial sources of SO2 include those involved in smelting ores, manufacturing steel, and refining
petroleum. Nationwide, the generation of electrical power at power stations that consume fossil fuel
emits as much SO2 as all other industrial sources combined. In many instances, major industrial sites
have self-contained power plants, and, even if the primary manufacturing process does not emit SO2,
the pollutant is present downwind of such industries. Important local sources Of SO2 include fossil-fuelfired furnaces used for space heating, refuse burning, and combustion of coal refuse piles.
The transportation industry emits some SO2 through exhaust systems, but concentrations are rarely
high enough to cause damage as a single pollutant. Sulfur dioxide is also emitted from natural sources
such as furnaroles and volcanoes.
Symptoms
Sulfur dioxide injury to forest trees is restricted to localized areas immediately downwind from point
sources. Foliar injury, typically most severe near the source of sulfur dioxide, decreases with distance
from the industry. However, if the industry has tall smokestacks, as do many power plants, then injury
to forests may occur 5 to 10 miles (8 to 16 km) downwind, where the plume touches down. Emissions
from industries located in valleys usually cause more sulfur dioxide injury to adjacent forests than do
emissions from sources located in flat or tolling, well-ventilated terrain. Forests on the sides of the
valleys or on adjacent ridgetops may show severe sulfur dioxide injury.
Broadleaf species: Acute sulfur dioxide injury to broadleaf trees is usually observed as ivory to brown,
bifacial, interveinal necrosis. The injured areas may appear initially as water-soaked, dull green areas
between the veins, but this symptom is seldom observed in the field. As the injured tissue dies and dries
out, the more typical symptoms occur. Leaves or leaflets with pinnate veination respond to sulfur
dioxide with the classic herringbone response; i.e., injured interveinal tissue turns ivory or brown, while
the tissues of and immediately adjacent to the veins remain uninjured and green. Examples of this type
of acute injury pattern are shown on a single leaf of sweet birch and American chestnut and on a
pinnately compound leaf of ash (Figures 20-22). In each case, the pinnate veination pattern has
determined the final injury pattern induced by sulfur dioxide. Although beech trees also have pinnate
veination, acute sulfur dioxide injury may be more marginal than interveinal (Figure 23).
Figure 20. Bifacial interveinal necrosis on sweet birch leaf exposed to SO2.
Figure 21. Bifacial interveinal necrosis on leaf of American chestnut sprout exposed to SO2.
Figure 22. Bifacial interveinal necrosis on leaflets of white ash exposed to SO2.
Figure 23. Marginal necrosis with some interveinal necrosis on American beech leaves exposed to SO2.
Leaves or leaflets with palmate veination, such as maple leaves, also show acute sulfur dioxide injury
between the veins (Figure 24). Since this vein pattern is more fan-shaped, however, the resultant
pattern is not a herringbone.
Figure 24. Interveinal necrosis on red maple leaves exposed to SO2.
Chronic sulfur dioxide injury or injury to a more tolerant species appears as chlorotic areas between the
leaf veins (Figure 25). This injury pattern is more difficult to diagnose in the field, since other stresses
cause similar patterns. Note that the injury pattern is similar to that of acute injury but is slightly more
diffuse.
Figure 25. Interveinal chlorosis on elm leaves exposed to SO2.
Oak foliage exposed to sulfur dioxide shows an even less classic response. The veination pattern of red
oak leaves, as well as some inherent mechanism that governs response, produces irregularly shaped
patches of tan, dead tissue across the leaf surface. This blotchiness can be seen on red or black oak that
has been exposed to sulfur dioxide (Figure 26).
Figure 26. Irregular pattern of bifacial necrosis on black oak leaves exposed to SO2.
White oak and chestnut oak respond to SO2 with more typical symptoms (Figure 27).
Figure 27. Bifacial necrosis on white oak leaves exposed to SO2.
Interveinal tissue injured by sulfur dioxide is not always brown or tan. Leaves with high levels of
anthocyanin pigments, such as dogwood or black gum, produce a reddish interveinal response to sulfur
dioxide (Figure 28). Injured hickory leaves show a reddish brown discoloration, whereas aspen or poplar
leaves form reddish brown to black injury patterns. As the injured tissue on broadleaf species weathers,
it often darkens with age (Figure 29).
Figure 28. Dark, reddish interveinal pigmentation on leaves of a dogwood shrub exposed to SO2.
Figure 29. Old bifacial necrosis on quaking aspen leaves exposed to SO2.
Leaves that have recently matured appear to be most sensitive to sulfur dioxide. Therefore, species with
determinant terminal growth, such as oak and ash, are more sensitive to sulfur dioxide early in the
summer. Species with indeterminate growth patterns have leaves in a sensitive growth stage
throughout the summer.
Conifer species: Sulfur dioxide injury to conifers is very difficult to diagnose. During the summer,
diagnostic efforts should always be complemented with observations of broadleaf plants that produce
more typical symptoms. Sensitive pine trees, such as eastern white, Scots, and Virginia, appear to be
most sensitive to sulfur dioxide early in the summer while the needles are still elongating. Injury appears
as a reddish brown discoloration of the needle tips, or, in severe cases, of the entire needle, except for
the tissue adjacent to the fascicular sheath (Figures 30-32). Elongation of the needles from their
meristematic base extends the area of injured tissue farther along the length of the needles. Later in the
summer, the most sensitive tissue is located in a narrow band; sulfur dioxide exposure at this time
results in a banding pattern of injury (Figure 33). Current year pine needles showing severe injury
seldom drop off. In contrast, spruce trees damaged by sulfur dioxide during the spring or summer
usually lose their current-year needles (Figure 34). Injured larch needles tend to remain on a tree longer
than do damaged spruce needles but not as long as injured pine needles.
Figure 30. Tip necrosis on Scots pine needles exposed to SO2.
Figure 31. Tip necrosis on immature needles of eastern white pine exposed to SO2 in June.
Figure 32. Tip necrosis on recently mature needles of eastern white pine exposed to SO2 in late July.
Figure 33. Tip necrosis with banding pattern, common on Austrian pine exposed to SO2.
Figure 34. Current-year needle abscission on Norway spruce exposed to SO2.
Grass and herbaceous species: At low concentrations of sulfur dioxide, the tips of several
monocotyledonous species become yellow, as do tissue areas parallel to the longitudinal veins. Higher
concentrations cause leaf tip and interveinal necrosis, which is characteristically ivory or light tan.
Sensitive species include annual bluegrass, oats, barley, wheat, gladiolus, and lily.
Bioindicator species: When sulfur dioxide injury is suspected, associated vegetation of the woodlands or
adjacent open areas should be examined. Within the forest, tree seedlings show symptoms similar to
those of mature trees. Sensitive bioindicator species, such as sarsaparilla, which occurs in the shade of
more closed canopies, may be useful indicators (Figure 35). In nearby fence rows, one can usually find
blackberry, which is one of the most sensitive species (Figure 36), or raspberry, which is only slightly less
sensitive (Figure 37). Bracken fern, found in open areas, is sensitive to SO2 until normal foliage browning
begins in late summer (Figure 38). Disturbed areas with bare soil may have giant ragweed, another
excellent indicator species (Figure 39).
Figure 35. Bifacial necrosis on sarsaparilla leaves exposed to SO2.
Figure 36.Interveinal bifacial necrosis on blackberry leaves exposed to SO2.
Figure 37. Interveinal bifacial necrosis on raspberry leaves exposed to SO2.
Figure 38. Tip necrosis on fronds of bracken fern exposed to SO2.
Figure 39. Ivory-colored, bifacial necrosis on giant ragweed exposed to SO2.
Concerns in Diagnosis
Sulfur dioxide injury is usually associated with point sources, and injury patterns resemble plume
dispersion patterns; therefore, distance and direction from known SO2 sources must be noted. Several
other agents may induce symptoms similar to SO2 injury, including leaf diseases incited by fungi, insects,
and nutrient deficiencies. Other stresses that induce similar symptoms include drought, frost, and
pesticide exposure.
Hydrogen Fluoride
Hydrogen fluoride (HF) pollution is most often a localized problem for two reasons: (1) the sources
generally release the pollutant close to the ground, thereby limiting the dispersal of fluoride in the air,
and (2) HF is very reactive and is quickly absorbed or adsorbed by buildings, soil, or vegetation. When HF
is released from tall stacks above the ground, it may be scrubbed from the plume by other pollutants.
Hence, fluoride problems usually occur within a few miles of a source of the pollutant. Under certain
mountain and valley conditions where an industrial plume is not readily dispersed, effects of the
pollutant can be observed at distances up to 12 miles (19 km).
Sources
Fluoride may occur in many forms, but the two most common are HF and silicon-tetrafluoride (SiF4).
Both gases are emitted during heating or chemical treatment of fluoride-containing rocks and minerals.
Fluoride may reach the plant as a gas, a particle, or a gas adsorbed onto particles. The most important
phytotoxic form of fluoride is HF gas, but particulate forms may be toxic if they exist as highly soluble
salts. Natural sources of HF include volcanoes and fumaroles, which can emit large quantities of the gas
into the atmosphere and cause localized problems for both plants and animals. The most important
sources of fluoride are industrial processes such as the manufacture of aluminum, phosphate fertilizer,
glass, bricks, steel, and chemicals, and the combustion of coal for heat or steam.
Symptoms
Symptoms can result from an exposure to high concentrations of HF for short periods of time or to very
low concentrations for days, weeks, or months. Symptoms generally appear as chlorotic or necrotic
areas near the margins of leaves (Figures 40-44). In such cases, measurable and elevated concentrations
of fluoride are found in affected leaf tissue and are diagnostic. In general, conditions that favor rapid
growth of the plant - and therefore open stomata - also favor injury from fluoride exposures. Genetic
variation has been reported to affect symptom expression in forest trees, resulting in severely injured
trees being adjacent to healthy trees in the same field.
Figure 40. Marginal chlorosis on a sweetgum leaf exposed to hydrogen fluoride.
Figure 41. Marginal chlorosis on sugar maple leaves exposed to hydrogen fluoride
Figure 42. Marginal chlorosis on hickory leaves exposed to hydrogen fluoride.
Figure 43. Marginal necrosis on sumac leaves exposed to hydrogen fluoride.
Figure 44. Marginal chlorosis on an ash leaf exposed to high concentrations hydrogen fluoride.
Trees on the edges of forest stands near sources of fluoride are the most likely to be injured, since the
HF concentration diminishes rapidly inside a stand. in open stands, injury may be uniformly distributed
within the population, and plants growing alongside openings within the stand may also be injured.
Injury usually occurs at the tops of trees where foliage is exposed. Severe exposures to fluoride may
produce a visible gradient or distinct area of vegetation injury close to the source.
Broadleaf species: Symptoms of fluoride on broadleaf plants consist of chlorosis of varying severity,
necrosis, or both. Symptoms appear first at the margins or tips of leaves, where fluoride accumulates;
with increasing severity, the symptoms extend toward the middle of the leaf Severe exposure can cause
necrosis of tissues between veins similar to that caused by sulfur dioxide, except that fluoride does not
bleach the necrotic area. Chlorosis is not usually present on leaves exposed to high concentrations of
HF. In many species, the necrotic tissue is reddish brown. Expanding leaves are generally most
susceptible.
Less severe exposures may cause a mild marginal chlorosis or anthocyanosis. In addition, leaves may
become cupped, indicating retarded growth at the tips and margins of the leaves (Figures 45, 46). In
many instances, the cupping is related to a notched tip or small necrotic area on the leaf tip which may
have broken off and is, therefore, no longer visible.
Figure 45. Anthocyanosis and cupping of blueberry leaves exposed to hydrogen fluoride
Figure 46. Chlorosis and cupping of sassafras leaf exposed to hydrogen fluoride. Note uninjured leaf on
left.
Conifer species: Symptoms of fluoride injury on conifer needles may easily be confused with symptoms
caused by other pollutants. The most common symptom observed on conifers exposed to HF is tipburn,
or necrosis of the needle tips (Figures 47-50). The inury pattern is uniform over the exposed portion of
the tree (Figure 51). The more severe the exposure or the more fluoride accumulated, the greater the
extent of the necrosis. The boundary between living and dead tissue is distinct and even. Necrotic tissue
directly adjacent to the living tissue may be a shade darker than the remaining dead tissue, and
sometimes a reddish band develops (Figure 52). Subsequent exposures may produce additional bands of
necrotic tissue, each with a ring of darker tissue demarcating the extent of the previous injury.
Exposures that cause necrosis are of three types: (1) a single severe exposure that causes death of the
entire length of needle, (2) a series of severe exposures that cause sequential areas of necrosis, or (3) a
series of longterm exposures at lower concentations that cause elevated fluoride concentration high
enough to cause tip necrosis in needle tissues.
Figure 47. Tip necrosis on needles of eastern white pine exposed to hydrogen fluoride.
Figure 48. Tip necrosis on needles of slash pine exposed to hydrogen fluoride.
Figure 49. Tip necrosis on needles of Scots pine exposed to hydrogen fluoride.
Figure 50. Tip necrosis on needles of spruce exposed to hydrogen fluoride.
Figure 51. General needle necrosis on eastern white pine exposed to high doses of hydrogen fluoride.
Figure 52. Tip necrosis and chlorosis on loblolly pine needles exposed to hydrogen fluoride.
Mild exposure to HF may cause chlorosis of the needle tips, but this symptom generally appears on no
more than a few millimeters of the needle length.
Grass and herbaceous species: Symptoms on monocots fall into two categories: stippling and flecking,
and tip necrosis. In grain plants such as wheat, barley, and corn, chlorotic stipples first appear at the tips
and margins of the leaves. As the severity of exposure increases, stipples form down the margins from
the tips and inward toward the midrib. The stipples may coalesce to form chlorotic bands. Necrosis
follows the same general pattern, beginning at the leaf tip and extending inward and down the margins
of affected leaves.
Bioindicator species: Bioindicators of fluoride pollution may be either plants that are extremely sensitive
to the pollutant and show visible symptoms, even from mild exposure, or plants that accumulate
fluoride from the atmosphere in a predictable fashion. Among the best indicators those that respond by
producing visible symptoms are redbud, catbrier, St. John's wort, wild grape, birch, and young expanding
needles of most pines and spruces. Nonforest species that may serve as bioindicators include gladiolus
and field or sweet corn. In plants such as gladiolus, symptoms begin with tip necrosis (Figure 53). Similar
symptoms are observed in tulip, iris, lily, and some other monocots.
Figure 53. Tip and marginal necrosis on Gladiolus exposed to low concentrations of hydrogen fluoride.
A second type of bioindicator program requires chemical analysis of plant tissue to determine fluoride
concentrations. In such a program, it is desirable to use a plant that is a good accumulator of fluoride
but does not have a high natural level in leaves. Species such as grasses and pines are good choices;
dogwood and hickories are not, because they accumulate fluoride from the soil.
Concerns in Diagnosis
In the field, symptoms may be infrequent or atypical of those normally associated with fluoride
pollution; it is important, therefore, to establish the suspected sources of the pollutant. Fluoride
problems are generally localized to an area within a few miles of the source, except under special
circumstances. If the area of impact is far removed from a source, alternative causes should be
considered.
After the source has been located, a survey should be conducted to establish the pattern of injury
around it; the incidence and severity of injury usually increase as distance from the source decreases.
The appearance of species known to be sensitive should be noted. Symptoms may or may not be
uniformly distributed, depending on the exposure of the plant. As part of the survey, the same species
of plants should be observed at sites that are physically similar but far removed from the source of
pollution in order to establish that symptoms are absent under clean-air conditions.
Forest Tree Diseases
Numerous forest tree diseases occur in the temperate regions of the eastern United States. In many
instances, these diseases have symptom complexes similar to those induced by air pollutants. Causal
agents range from simple abiotic stress, such as prolonged drought or spring frost, to complexes of
fungi, insects, and abiotic stresses. In this section, the examples of leaf diseases, twig and stem cankers,
root diseases, and slowly occurring diebacks and declines reveal similarities between symptoms of these
diseases and symptoms caused by air pollutants. In many instances, the biotic pathogen being reviewed
has not been associated with specific sites; however, its general range has been presented.
This section of the manual is divided into two parts: Hardwood Diseases and Conifer Diseases. Both
parts are organized by disease types, based on the part of the tree affected and on symptom
expressions. The causal agent for each disease is also presented.
Hardwood Diseases
Diebacks and Declines
In recent decades, dieback and decline diseases have killed or damaged millions of trees in the eastern
United States. Most hardwood tree species are affected by these disorders at some point, but relatively
few species have suffered greatly. Most dieback and decline diseases of forest trees share a common
type of cause-and-effect relationship that serves to define and differentiate them from other types of
disease.
The syndrome shared, in part or in whole, by many of these diseases frequently has two phases - a
dieback phase and a decline phase. The term dieback-decline is a descriptive label that implies a
progressive development of symptoms, beginning with the dying back of buds, twigs, and branches,
progressing inward and downward, and culminating in the decline and death of the tree. Leaves of
declining trees are often small, sparse, and off-color; foliage in successive years is borne on sprouts and
may appear clumped or tufted; leaves show premature fall colors and drop; and terminal and radial
growth is often reduced even before external symptoms appear.
Diebacks and declines are complex diseases initiated by adverse environmental factors that create biotic
and abiotic stress and often culminate in lethal attacks by organisms that are otherwise not harmful.
Thus, these diseases differ from those caused by single primary pathogens in that trees suffer from a
multiplicity of abiotic and biotic stress factors. In the context of these diseases, predispositional stress
refers to environmental pressure sufficient to trigger changes in the physiology, form, or structure of a
tree. The stress factors can be abiotic (e.g., extremes of moisture or heat) or biotic (e.g., insect
defoliation, scale or aphid attack, infection by fungi, or combinations of these). In the absence of such
stresses, the organisms of secondary action, often ubiquitous in the ecosystem, occupy various niches
ranging from saprophyte to weak pathogen. Without these organisms, trees would most likely recover
when the stress abates. This common cause-effect definition can be expressed as a series of stages:
1.
Healthy trees + stress altered trees (dieback begins)
2.
Altered trees + more stress = trees altered further (dieback continues)
3.
die.
Significantly altered trees + organisms of secondary action = trees invaded, decline, and perhaps
These statements imply that the dieback stage often results from stress alone and that when stress
abates without lethal attacks by secondary organisms, dieback often ceases and trees recover. The
decline stage, in which vitality lessens and trees succumb, usually occurs when organisms attack the
stress-altered tissues. Recovery from this phase, which is less likely than recovery from the dieback
stage, depends on such factors as tree vigor, location and severity of tissue invasion, and aggressiveness
of the secondary organisms involved.
These statements do not imply that severe stress, if repeated or prolonged, cannot by itself cause a
decline of tree vigor and even death.
Because diebacks and declines are frequently initiated by broad environmental changes, they may
suddenly emerge over a wide area, and the types of sites where they develop may appear to be closely
related.
Oak decline and mortality (Figure 54) over large areas of Pennsylvania, West Virginia, New York, and
many other states is related in time and place to drought and severe insect defoliation. Similarly, a
dieback of white and green ash (Figure 55), triggered by defoliation caused by the ash rust fungus, is
limited to coastal regions by the restricted range of the alternate hosts, the salt marsh grasses. In
Massachusetts, an extraordinarily high number of maple disorders not attributable to primary
pathogens occurred regularly two years after periods of severe water shortages. A decline in the
roadside sugar maple population (Figure 56) and beech bark disease (Figure 57), triggered by
applications of winter road salt and infestations of beech scale insects, respectively, is obviously related
in time and place to these initiating stresses.
Figure 54. Oak decline and mortality in a mixed oak/hickory stand. Branch dieback and whole tree
mortality are present.
Figure 55. Ash dieback with typical symptoms of reduced viable crown and abundant sprouting along
main stem and lower branches.
Figure 56. Decline of roadside sugar maple; in this case, most likely due to deicing salt application and
subsequent uptake through roots.
Figure 57. Beech bark disease on an isolated American beech, leading to mortality and a hole in the
forest canopy.
The diagnosis of dieback and decline disease involves the following procedures:
1.
Recognizing symptoms, including progressive dieback and deterioration of crowns; thin, sparse,
tufted foliage produced on main stem sprouts; early fall coloration; and reduced height and radial
growth rates.
2.
Identifying which events may have triggered the problem. Records of disturbances such as
weather extremes, insect defoliation, fire, and logging activity are extremely valuable. Identifying when
disturbances happened by examining growth ring patterns or age of sprout tissues may help to pinpoint
the disturbances and when they occurred.
3.
Determining the presence and developmental stage of secondary organisms, such as rootinvading and twig-cankering fungi and bark borers. This determination also helps to confirm the
diagnosis and date of the events that triggered these attacks.
Knowing when and where significant disturbances occur today will help predict when and where they
may occur tomorrow. It is also important to realize that a multitude of stress-host interactions can
trigger dieback and decline diseases and that only diligent observation can determine the underlying
factors. Several examples of important diebacks and declines are discussed in more detail in the
following sections.
Maple Decline
Disease description: Early symptoms of maple decline include late foliage flush in the spring, smaller,
slightly chlorotic leaves, twig dieback, reduced growth, and premature leaf coloration in mid-to late
summer. Lateral buds on dying twigs sprout, producing tufts or clumps of foliage that may be off-color in
the spring (Figure 58). Twig dieback appears initially in the upper branches; the progressive death of
branches inward and downward yields the characteristic stagheaded tree (Figure 59).
Figure 58. Foliage discoloration on sugar maple suffering from maple decline.
Figure 59. Top dieback or "staghead" symptom of maple decline on sugar maple.
Death of weakened twigs and branches can be hastened by attacks of weakly pathogenic fungi, such as
Stegonosporium ovatum. Roots of weakened trees are often rapidly invaded and killed by the shoestring
root rot fungus, Armillaria. (See oak decline for details on Armillaria.)
Cause: Maple decline in the forest often occurs after defoliation by a number of insects, including
leafrollers and webworms, the saddled prominent, and the forest tent caterpillar. More recently,
drought and severe winters with little snow cover have been linked to maple decline.
Suscepts: Maple decline is primarily a disease of sugar maple and occurs throughout its range. Crown
deterioration of red maple has been observed in forests after gypsy moth defoliation as well as during
and immediately after years of heavy seed crop.
Range and site description: Decline has been observed throughout much of the range of the two
suscepts. Pockets of decline may be found across many sites, depending upon the agents involved, e.g.,
droughty soils or those recently attacked by defoliating insects. Many sugar maple trees have declined
and died in the Northeast. While the reasons for this are not thoroughly understood, the decline has
been most severe in sugar maple stands subjected to drought, heavy grazing, or overtapping and heavy
traffic by farm machinery used in sap gathering. Many of the seriously affected trees are overmature
and have been heavily tapped for many years. These trees are usually riddled with stain and decay
associated with tapholes and root wounds; insect defoliation often accelerates decline in these stands.
Diagnostics: Look for current evidence of defoliating insects, fungal fruiting structures on leaves,
rhizomorphs of Armillaria under the bark at the base of the tree or along excavated roots, and/or
sporophores of Armillaria at the base of trees or stumps. Look at site specificity, i.e., droughty soils and
frost pockets. Compile site history from previous records of insect-caused defoliation, sugarbush
operations, fire, logging, and so on.
Sapstreak Disease Of Sugar Maple
Disease description: The first noticeable symptom of sapstreak of sugar maple is a dwarfing of the
foliage on all or a portion of the crown; dwarfing becomes more intense and may spread to previously
unaffected parts of the crown in following years (Figure 60). In addition, some branches may begin dying
back. Trees without crown symptoms one year may fail to leaf out the next, while others may die a year
after the first foliar symptoms. Some trees linger for several years, exhibiting repeated sequences of
crown dieback and recovery, until they finally die.
Figure 60. Poorly developed small leaves on sugar maple due to sapstreak disease, resulting in thin and
ragged crowns,
Inside the tree, the wood of buttress roots and lower stems exhibits a stain of distinctive color and
pattern (Figure 61). When freshly exposed, the stained tissue is yellowish green, is bordered by a thin,
dark green margin, and appears water-soaked. Reddish flecks are visible in freshly exposed stain areas.
Within a few minutes of exposure to air, the stain darkens dramatically and the red flecks become less
discernible. On drying, the discolored tissues fade to a light brown. In cross section, the stain appears to
radiate outward toward the bark in fingerlike or starlike projections. Cambium infiltrated by the stain
dies and cankers develop. In severely diseased trees, this radiating pattern disappears as the entire cross
section of roots becomes stained.
Figure 61. The wood of a buttress root of sugar maple, showing streaking and discoloration due to
sapstreak disease.
Cause: Sapstreak disease is caused by the fungus Ceratocystis coerulescens. This fungus is a common
stainer of hardwood logs and lumber, but it sometimes can enter and kill living trees as well.
Suscepts: Sugar maple is the most common suscept.
Range and site description: Sapstreak has been reported in North Carolina, Michigan, Wisconsin,
Vermont, and New York. It is very likely, however, that the disease occurs throughout the range of sugar
maple wherever the conditions for infection occur in the presence of the causal fungus. The fungus
appears to enter the tree primarily through logging wounds, either on roots or near the base of the
trunk (Figure 62). Because such wounding may occur many years before symptoms develop, callus
sometimes nearly closes the wounds by the time the disease is recognized. Disease development seems
to be related to wounding involved in sugaring operations or in road construction and related
mechanical injuries.
Figure 62. Logging wounds at the base of a sugar maple, which may serve as entrance courts for the
sapstreak fungus.
Diagnostics: Look for small leaves, thin crowns, dieback, and stain of the wood in the buttress roots and
root-collar zones when exposed to air. Look for cankers near the groundline and note site conditions,
including recent logging or sugarbush operations.
Beech Bark Disease
Disease description: Beech bark disease results in significant mortality and defect in American beech.
The white wax secreted by the beech scale insect is the first sign of invasion. Isolated dots of white
"wool" appear on the bole of the tree on roughened areas of bark, beneath mosses and lichens, and
below large branches. Eventually, as the insect population increases, the waxy scales may cover large
areas of the bole (Figure 63).
Figure 63. Waxy secretions of beech scale insect evident on the bark of an American beech following a
heavy infestation.
Serious damage results only after the fungus Nectria invades scale-infested bark. Nectria produces two
types of spores: asexual and sexual. Asexual spores are produced in the summer in small, white cushions
that resemble the woolly wax produced by the scale. More obvious are the tiny, bright red, lemonshaped perithecia, which produce the sexual spores (Figure 64). Perithecia are often produced in
clusters on dead bark; they mature in the fall.
Figure 64. Red fruiting bodies (perithecia) of Nectria on the trunk of an American beech formerly
infested by the beech scale insect.
On some trees, a red-brown exudate called a slime flux or tarry spot oozes from dead spots. Tarry spots
are often the first symptom of Nectria infection. If the outer bark of an infected tree is cut away, a
distinct orange coloration may be seen where Nectria is actively invading the bark. The fungi may infect
large areas on some trees, completely girdling them. On such trees, large numbers of perithecia often
form, giving a reddish cast to extensive areas of the bark. On dying trees, leaves that emerge in the
spring do not fully enlarge, giving the crowns a thin, open appearance. Later, the leaves turn yellow and
usually remain on the tree during the summer. Although severely affected trees exhibit progressive
crown deterioration symptoms, they may live for several seasons. The rate of crown decline depends
primarily on the severity of scale and fungus attack.
The fungus frequently infects only narrow strips or patches on the bole, and the resultant symptoms
differ from those of girdled trees. Callus tissue forms around these areas, and the bark becomes
roughened (Figure 65). Callus tissue may wall off small Nectria cankers from the remainder of the living
sapwood.
Figure 65. Sunken and callused-over cankered areas on American beech tree severely affected with
beech bark disease.
Cause: Beech bark disease occurs when bark that has been attacked and altered by the beech scale
insect, Cryptococcus fagisuga, is invaded and killed by one of two fungi, Nectria coccinea var. faginata or
N. galligena.
Suscepts: American beech is susceptible. Although small beech trees can be infested by beech scale and
infected by Nectria, heavy attacks are rare. Consequently, mortality is significant only in trees with a
diameter larger than about 8 inches (20 cm).
Range and site description: Beech scale has been found in Quebec and throughout New England, New
York, New Jersey, and northern and eastern Pennsylvania. Recently it has been found infesting stands in
northeastern West Virginia, in adjacent areas of Virginia, and in several counties in northeastern Ohio. It
seems likely that the disease will continue to spread throughout the range of beech.
Diagnostics: The pattern of insect spread and the subsequent occurrence of Nectria infection and tree
death have led to the following arbitrary classification of disease development over time and space:
•
The advancing front - areas recently invaded by beech scale and characterized by forests with
many large, old trees supporting scattered, sparse, but increasing populations of beech scale.
•
The killing front - areas characterized by high populations of beech scale, severe Nectria attacks,
and heavy mortality of trees.
•
The aftermath zone - areas that at some time suffered heavy mortality and that now have some
residual large trees and many stands of small trees, often of root-sprout origin. In the aftermath zone,
young stems are often rendered highly defective by the interactions of beech scale, Nectria, and another
scale insect, Xylococculus betulae.
Caution must be exercised in diagnosis, since thin crowns and small chlorotic leaves are general
responses to other stresses. Chlorosis of beech, for example, can result from an iron deficiency.
Oak Decline
Disease description: Trees affected by oak decline show a general and progressive dying back from the
tips of the branches (Figure 66). Other symptoms include chlorotic, dwarfed, and sparse foliage; sprouts
on main branches and stem; and premature autumn leaf color and leaf drop. Growth decline is also
evident.
Figure 66. Early decline and crown dieback symptoms on an unidentified oak species with typical twig
and small branch dieback evident.
As dieback and reduced growth continue, larger branches die and form the characteristic stagheaded
crown. Foliage is mainly limited to sprouts on the larger branches and main stem. Trees eventually
succumb, sometimes suddenly, to the root-killing and girdling actions of secondary insects and diseases.
The two major pests associated with oak decline are Armillaria mellea, the cause of shoestring root rot,
and Agrilus bilineatus, the two-lined chestnut borer.
The common forest fungus, Armillaria, attacks the roots of stressed oaks from rootlike structures called
rhizomorphs that grow through the soil and over the surface of tree roots (Figure 67). Infection
eventually girdles 1 the large buttress roots and root collar and kills the tree. White mycelial fans may
form under the bark (Figure 68), and, in autumn, clusters of honey-colored mushrooms may form at the
base of invaded trees (Figure 69). Agrilus bilineatus attacks the branches and stems of weakened trees;
the larvae begin feeding and form meandering galleries in the inner bark and outer wood (Figure 70).
These borers first infest branches in the upper crown; later infestations are lower, often reaching the
base of the tree. The combined actions of the borer in the stem and the fungus in the roots can bring
about rapid decline and death. Final symptoms of oak decline reflect the root-killing and girdling effects
of these organisms. Leaves sometimes fail to develop in spring, wilt shortly after budbreak, or suddenly
wilt or turn brown late in the growing season.
Figure 67. Shoestring-like rhizomorphs of Armillaria covering a piece of fallen wood. Such structures are
evident under the bark of roots and lower stems.
Figure 68. White mycelial fans of Armillaria under the bark of trees suffering from crown dieback and
mortality.
Figure 69. Cluster of honey-colored Armillaria mushrooms at the base of an infected tree. Clusters may
be formed along roots or slightly higher up the stem.
Figure 70. Feeding galleries of the two-lined chestnut borer, which attacks oaks in various stages of
dieback and mortality.
In some instances, decline and death may occur over a short period of one to two years or even within
one growing season. Such declines are usually seen on ridges or other drought-prone areas (Figure 71).
Symptoms develop rapidly and usually involve the entire crown; all leaves turn brown but remain
attached throughout the growing season. Short-term declines are most common in suppressed,
overtopped, and/or otherwise stressed trees.
Figure 71. Seasonal decline, dieback, and mortality of oak on ridges, following defoliation by insects or
persisting drought conditions.
Another characteristic of short-term decline throughout the Southeast is the almost universal
occurrence of the sap-rotting fungus, Hypoxylon atropunctatum, on boles and larger branches of
affected trees. This fungus, a bark inhabitant, is an early, rapid colonizer of the sapwood of stressed or
recently dead red oaks, white oaks, and hickories. Presence of the solid, black-fruiting bodies of this
fungus on tree stems can reliably indicate an immediate past history of biotic or abiotic stress (Figure
72).
Figure 72. Fruiting bodies of Hypoxylon, which has invaded and colonized the bark and sapwood of a
dying oak as part of the oak decline complex.
Cause: Oak decline is stress initiated, the most frequent stress factors being drought, frost injury, and
insect defoliation. Trees on dry ridge tops and in wet areas suffer the most from major fluctuations in
moisture conditions that lead to severe drought injury. Frost often affects trees growing in valleys and in
associated frost pockets. Defoliated trees that refoliate the same season may exhibit dieback symptoms
the next year. Other factors such as leaf diseases and waterlogged, compacted, or shallow soils have
been implicated in oak decline. Waterlogging is especially important in the heavy clay soils of the
Midwest. These stress factors weaken trees so that they succumb, sometimes suddenly, to pathogenic
organisms and insects.
Suscepts: Oak decline has occurred throughout the range of oak in both forests and in urban
environments. The most frequent and severe outbreaks have been in southern New England, the Middle
Atlantic states, and the Southeast. Red, scarlet, pin, and black oak in the red oak group and white and
chestnut oak in the white oak group are the most significantly affected species.
Range and site description: This disease may be found on specific sites throughout the range of oak. A
characteristic feature of oak decline is its sudden development on many trees over large areas affected
by the initiating stress factor. Within the affected areas, decline and mortality may be in patterns,
reflecting the intensity and severity of the stress, distribution of hosts, aggressiveness of Armillaria
mellea, abundance of two-lined chestnut borers, and other site features such as frost pockets and dry,
shaly soils.
Diagnostics: Look for current evidence of defoliating insects, fungal fruiting structures on leaves,
rhizomorphs of Armillaria under the bark at the base of trees or along excavated roots, and sporophores
of Armillaria at the base of trees or stumps. Look at site specificity, i.e., droughty soils or frost pockets.
Compile site history from previous records of insect caused defoliation, fire, logging, and so on.
Wilt Diseases
Oak Wilt
Disease description: Oak wilt is a vascular wilt disease characterized by a sudden wilt of foliage in
infected trees. Observable symptoms appear from early June until leaf coloration is completed in the
fall. There are two distinctly different symptom patterns, depending upon the group of oaks affected.
• Red oak group: Symptoms are characterized by a sudden wilting of the leaves at the top of the tree;
wilting progresses downward through the crown very rapidly (Figures 73, 74). Wilting and water-soaking
(Figures 75, 76) of the leaves are most often accompanied by leaf fall before the leaves have turned
brown. Defoliation of the entire tree is usually complete in three to six weeks after infection. The
petioles of wilted leaves are black at the base, and the outer sapwood of diseased branches and main
stems may have a dark-streak discoloration. Identifying signs of the causal fungus are mycelial, ovalshaped pads, which are produced under the bark of infected trees three to nine months after wilting
and defoliation (Figure 77). Appearing in late spring and early fall, these black and gray pads force open
the bark; their fruit-like odor is very attractive to insects. Lightly tapping the bark for a hollow sound will
assist in locating these pads.
Figure 73. Rapid oak wilt development of red oak in Pennsylvania, ten days following an
inoculation by Ceratocystis fagacearum.
Figure 74. Crown of red oak, showing typical oak wilt symptoms consisting of severely wilted leaves and
rapid defoliation, leaving a thin, dying crown.
Figure 75. Oak wilt symptoms of chestnut and red oak leaves, showing the line of demarcation between
green and dying tissues. Water-soaking symptoms are evident on the leaf to the right.
Figure 76. Oak wilt symptoms of live oak leaves following infection by Ceratocystis fagacearum.
Figure 77. Oval mycelial mat of the oak wilt fungus found under the bark of dying or dead oaks. The mat
has a fruit-like odor.
• White oak group: Symptoms are characterized by a slow wilt of a single branch. Leaves usually remain
on the tree, and only the terminal portion of the affected leaves turns brown. Death of the entire tree is
rare but may occur one to four years after infection. The killing of individual branches over a period of
years, which causes stagheading of the crown, may be confused with oak decline. Fungus pads are only
rarely produced on infected white oaks.
Cause: Oak wilt is caused by the fungus Ceratocystis fagacearum. After the fungus invades the vascular
system of the tree, it induces formation of tyloses, which further hinder water transport. No other stress
agents are involved.
Suscepts: There are between 200 and 300 species and hybrids of oaks. To date, not one has proven
immune to the attack of the causal fungus. Species belonging to the red oak group (black, scarlet, pin,
southern red, and northern red oak) are more susceptible to infection than are species of the white oak
group (white, chestnut, swamp white, and post oak). American and oriental chestnut, chinkapin, tanoak,
and apple are also susceptible.
Range and site description: The range of oak wilt extends from Minnesota to Pennsylvania to North
Carolina to central Texas; however, it exists primarily in the mountainous section of the East, particularly
on west-facing slopes and ridgetops. The disease has not been found in New England, New York, New
Jersey, or east of the Susquehanna River in Pennsylvania. The disease may affect individual trees, but
there may also be centers of infection with numerous dead trees adjacent to currently wilting trees.
Spread by local root graft accounts for these infection centers. The rapidity of wilt and defoliation leading to death - in red oak is quite distinctive to this disease.
Diagnostics: Oak wilt, unlike oak decline, occurs in isolated trees or small pockets of trees with no
history of abiotic stress. Particularly in white oaks and sometimes in red oaks, laboratory diagnosis is
usually necessary to conclusively identify trees dying from infection by the oak wilt fungus.
Leaf Diseases
Most tree species produce an abundance of leaves far exceeding the numbers required for normal
growth. Therefore, unless severe defoliation takes place, enough leaf surface is usually left to produce
normal annual growth. When a tree loses all or most of its leaves to disease or other injurious agents,
poor vigor, growth loss, and even death may follow. Early summer refoliation, during which food
reserves are depleted as a second flush of leaves is produced, may eventually cause decline and death of
affected trees.
Most organisms that cause leaf disease are favored by cool, wet weather at the time of leaf
development in early spring. Only a few diseases develop late in the summer months when the weather
is hot and dry.
Numerous leaf diseases occur on eastern forest trees. Those of a fungal nature usually show evidence of
some type of fruiting structure, growth (zone) lines of increasing lesion size, or a distinctive symptom
pattern associated with veins or veinlets. Careful diagnosis is required to distinguish the representative
diseases presented below, as well as other disorders, from air pollutant-incited injury.
Anthracnose
Disease description: Anthracnose is characterized by sharply defined areas of dead tissue on affected
leaves. These areas usually are found in association with veins on the leaf, but, in severe cases, entire
leaves may die. Infected young leaves may become distorted due to the continued growth of
noninfected tissues on the periphery of infected, dying areas (Figure 78).
Figure 78. Anthracnose of ash leaves showing distortion due to necrosis of infected tissues,
Sycamores are particularly susceptible to infection by the anthracnose fungus, which may advance into
small twigs, where it causes cankers. Such infections may remain active for several years and may
eventually kill the terminal portions of twigs and branches.
Anthracnose of other species may be evidenced by smaller spots on the leaves that are black with
irregular borders. Small, dark fruiting bodies of the causal fungi may form on the infected tissues. With
the aid of a hand lens, one may see these fruiting bodies embedded in the dead tissues.
Severe infection of leaves causes defoliation during late spring and early summer. In some instances,
only the top of the crown remains unaffected, giving the tree a tufted appearance (Figure 79).
Refoliation of affected trees is usually poor and results in a very thin crown.
Figure 79. Anthracnose of sycamore; infection of leaves and twigs will result in thin crowns and a tufting
appearance of the top crown; both dead and green leaves may be found under the tree.
Cause: Anthracnose is caused by several species of fungi in the genus Gnomonia.
Suscepts: Most hardwood trees are susceptible to infection by the causal fungi. Sycamore, oak, maple,
horsechestnut, and black walnut are most severely affected. Hickory, ash, and several other minor
species are affected less severely.
Range and site description: While anthracnose is found throughout the United States, it is primarily a
concern in the eastern, southern, and central hardwood forests. Disease development is favored by
cool, wet weather in early spring.
Diagnostics: Sharply defined areas of dead tissue on leaves characterize anthracnose. This disease may
be confused with acute S02 injury. Extent of disease development and patterns of injury in the stand
should be noted. Examination of dead tissues for embedded fruiting structures will assist diagnosis.
Leaf Blister Of Oak And Other Species
Disease description: Leaf blister characterized by raised, wrinkled and brown blisters on affected leaves
during late summer or early fall (Figure 80). Initial symptoms involve a slight yellowing of the infected
tissues. Blisters form when the fungus stimulates cell growth after the surrounding infected cells
become rigid. These blisters are usually less than 1 inch (2 cm) in diameter, and the, remain light green
in color for several weeks before tissue death turns them brown. Severe infection results in numerous
blisters on a single leaf and thus leaf distortion also occurs. Premature fall may occur in early autumn.
Such defoliations stunt growth and may weaken the tree's resistance to attack by other agents. This
disease is favored by cool, wet weather in spring.
Figure 80. Leaf blister disease on red oak leaves, showing ragged, raised blisters in circular and coalesced
patterns.
Cause: The fungus Taphrina coerulescens causes leaf blister.
Suscepts: While all oaks are susceptible to leaf blister, black and red oaks are the most susceptible to
attack. Other species occasionally affected include poplar, birch, and cherry.
Range and site description: Leaf blister occurs throughout the United States but is important oaks only in
the East. A major disease of oaks in the southern United States, leaf blister occasionally causes 50 to 85
Percent defoliation of affected trees by midsummer.
Diagnostics: Initial yellowing of foliage, usually in a circular pattern, is quickly followed by formation of a
raised blister. Examination later in the season will detect raised dead areas and considerable leaf
distortion.
Leaf Rust Of Poplar And Larch
Disease description: This rust disease alternates between poplars and larches. The most significant
damage occurs on poplars, where up to a 20 percent reduction in radial growth has been observed
following repeated defoliations. Symptoms on poplar include yellow to orange bifacial spots, which
contain pustules of the rust fungus in the uredial, telial, and basidial stages (Figure 81). Spots later turn
purple-brown, and severely infected leaves fall prematurely (Figure 82). Dieback and mortality follow
repeated defoliations; defoliated trees have been shown to be more sensitive to winter injury.
Symptoms on larch include initial minute yellow spots, followed by the fungus producing more easily
seen fruiting structures on needle surfaces, e.g., the pycnial and aecial stages (Figure 83).
Figure 81. The uredial and telial spore stages of Melampsora medusae on poplar leaves. Note chlorotic
spotting on upper leaf surface.
Figure 82. Purple-brown spots on fallen leaves of poplar infected with the rust fungus, Melampsora
medusae.
Figure 83. The pycnial and aecial stages of Melampsora medusae on needle of larch; chlorotic spotting
precedes fruiting structure emergence.
Cause: Leaf rust of poplar and larch is caused by the fungus Melampsora medusae.
Suscepts: This rust disease occurs most commonly on hybrid poplars and eastern larch. It also occurs on
quaking aspen, eastern cottonwood, Douglas-fir, and several pines, spruces, and hemlocks.
Range and site description: The range of this disease includes much of the central and northeastern
portions of the eastern United States. It can occur wherever the alternate hosts exist in proximity to
each other but also may occur outside the range of larch or other alternate hosts due to wind
dissemination of the repeating spores (uredospores) from poplar to poplar.
Diagnostics: The disease is best identified by looking for the fungal signs present in the form of fruiting
structures on leaves of either alternate host. Fallen poplar leaves should be observed for these
structures. Purple spotting could be confused with chronic ozone injury.
Powdery Mildew
Powdery mildew affects many forest tree species but is not usually considered to be of any significance.
It is recognizable by the powdery white mycelium of the causal fungus and by numerous black fruiting
bodies on the lower leaf surface (Figure 84). This disease is prominent during dry weather from spring
until leaf drop in the fall. Infected leaves may appear chlorotic. Oaks are particularly susceptible.
Figure 84. Powdery mildew on lower leaf surface of an infected red oak. Small, black fruiting bodies of
the causal fungus are evident.
Phyllosticta Leaf Spot
Disease description: This disease is characterized by small, circular to somewhat irregularly shaped
brown lesions on leaf surfaces (Figure 85). Lesions may remain separate or may coalesce to cover almost
the entire leaf surface. Individual spots may have a very distinct purple border. Black fungal fruiting
bodies are embedded in the lesions on upper leaf surfaces. Infections in wet seasons may cause severe
defoliation.
Figure 85. Phyllosticta leaf spot on red maple, showing the zonate pattern of fungal colonization and
yellow halo around each infection spot.
Cause: The fungus Phyllosticta spp. causes this leaf spot.
Suscepts: Many hardwood species, especially maples, are susceptible to this fungus.
Range and site description: This disease is found throughout the range of its suscepts and is favored on
sites with cool, wet weather early in the growing season.
Diagnostics: The halo of purple tissue around individual lesions and the presence of fruiting bodies
embedded in the tissues assist in diagnosis. Zone lines may also be present within the lesion.
Tobacco Ringspot Virus Of Ash
Disease description: Following infection early in the growing season, faint chlorotic spots develop on ash
leaves; the spots may fade as the season progresses. Spots that develop further are normally less than
1/10 inch (1 mm) in diameter and appear to be diffused without a distinct margin between yellow and
green tissue. Chlorotic areas include the veins (Figure 86). Spots later coalesce to form diffuse complete
or partial rings. When numerous, rings may merge into a general chlorotic mottle. Infected leaflets
sometimes are crinkled and more stunted than noninfected leaves. Late in the growing season, spots
may turn reddish brown or may remain yellow-green, while the rest of the leaflet turns yellow or
reddish purple in the fall.
Figure 86. Chlorotic spot on ash leaflet; caused by tobacco ringspot virus.
The development of foliar symptoms on individual leaflets, twigs, or branches varies greatly. Sometimes
only a few scattered leaves on an entire tree are involved.
Cause: An ash isolate of the tobacco ringspot virus is the cause of this disease. The only known natural
vector is the dagger nematode, Xiphinema americanum.
Suscepts: All ages of white and green ash appear to be susceptible. Tobacco ringspot virus becomes
systemic in ash, as in other hosts, but symptom expression varies considerably during the growing
season and on a year-to-year basis.
Range and site description: From only limited survey work, virus infected ash have been confirmed in
several sites in New York. From observations of field symptoms elsewhere, it is likely, but unproven, that
the disease extends over much of the range of ash in the northeastern states. Symptoms indicative of
virus infection have been observed on a variety of different woodland, hedgerow, and homeowner sites,
regardless of soil quality or type.
Diagnostics: Distinctive patterns of foliar symptoms, e.g., chlorotic spots or ringspots, are scattered on
leaves but rarely over the entire crown. When the chlorotic spots turn brown to reddish brown late in
the growing season, the symptoms may resemble the flecking caused by oxidant air pollutants.
Tobacco Mosaic Virus Of Ash
Disease description: In May and June, infected foliage shows chlorotic spots and ringspots, a pale green
coloration, and sometimes interveinal chlorosis. In June and July, symptoms consist of chlorotic spots,
rings, and mottle; occasionally, chlorotic, light green, or whitish line patterns may appear along the main
veins (Figure 87).
Figure 87. Line or ring pattern on ash leaflet; caused by tobacco mosaic virus.
Cause: Tobacco mosaic virus causes this disease.
Suscepts: White and green ash are susceptible.
Range and site description: This disease has been identified in ash in New York and Massachusetts and is
widespread in ash in all probability because of the stability and ease of transmission of tobacco mosaic
virus. No site-specific relationships have been reported.
Diagnostics: Some of the foliar symptoms of tobacco mosaic virus infection in ash resemble those
caused by tobacco ringspot virus and could, therefore, be confused with oxidant-induced injury.
Patterns and locations of symptoms should be noted.
Ash Yellows
Disease description: Trees infected by the ash yellows organism are characterized by chlorotic to pale
green, undersized leaves (Figure 88). Infected trees have thin crowns with twig and branch dieback and
premature purplish autumn coloration. Small witches' brooms may appear at the ends of branches, and
abundant epicormic branches and brooms appear along the main stem in advanced stages of disease
development (Figures 89, 90).
Figure 88. Ash yellows disease of American ash, showing chlorotic and small leaves, thin crowns, and
dieback of the crown.
Figure 89. Ash yellows mycoplasma-infected leaves and induced witches' broom on American ash.
Figure 90. American ash twigs showing greatly reduced internode length and deliquescent branching
patterns following infection by the ash yellows mycoplasma.
Cause: Ash yellows is caused by a mycoplasma-like organism which infects the phloem.
Suscepts: White ash is the primary host of the causal organism, In addition, green ash and several other
ash species are susceptible.
Range and site description: This disease has been observed throughout the New England states and in
New York, New Jersey, Wisconsin, and Indiana. The exact range has not been established. The disease
does not appear to be site specific and has been found in forest, hedgerow, park, and home landscape
trees. Infection centers are evident under forest conditions.
Diagnostics: Small yellow leaves, thin crowns, and witches' brooms are evidence of the presence of this
disease. The occurrence of the disease in infection centers within forest stands is also diagnostic. The
causal agent is visible only with the aid of light or transmission electron microscopes.
Line Pattern Of Birch
Disease description: The most predominant symptom of this disease is a pattern of chlorotic lines
forming a jagged-edge design, irregular concentric rings, and/or chlorotic flecks (Figure 91). Symptoms
occur as the leaf enlarges and are complete once leaves are fully expanded. Later growth shows milder
symptoms.
Figure 91. Line pattern on birch; caused by apple mosaic virus.
Symptoms appear on large trees as well as on small, one- to two-year-old seedlings. Leaf symptoms can
appear anywhere within the crown; the most obvious signs appear in spring. The virus is biologically
capable of being transmitted in seeds. Small trees in the understory often show symptoms of the
disease.
Cause: Apple mosaic virus causes this disease.
Suscepts: White and yellow birch are both susceptible.
Range and site description: Line pattern symptoms on birch have been seen in the northeastern United
States, in eastern Canada, and in Wisconsin. This disease might be expected to occur wherever birch
grows. There are no site-specific relationships known.
Diagnostics: Distinctive line symptom patterns are evident on infected leaves; most often, only a small
number of leaves show symptoms.
Conifer Diseases
Root Diseases
Annosum Root Rot
Disease description: Annosum root rot is a major disease of pines and other conifers, causing growth
loss and mortality in plantations and natural stands. The disease is most severe in thinned stands where
stump surfaces and root wounds are points of entry for the fungus. Severely affected trees grow more
slowly and are more susceptible to attack by bark beetles. Tree mortality tends to be in pockets, but it
may be uniformly distributed throughout severely affected stands.
Foliage of infected trees may appear healthy or may be colored from light green to yellow-brown.
Branches may have only current-year needles that may be shorter than normal, giving the crown a thin,
tufted appearance (Figure 92). These symptoms may be easily confused with pollutant-induced injury.
Wind-thrown or leaning trees may also be present in severely affected stands, especially on sandy soils.
Roots of infected trees are initially resin-soaked and brownish red (Figure 93), later becoming white,
stringy masses of decayed tissue (Figure 94).
Figure 92. Mortality yellowing and thin crowns of loblolly pine; caused by root disease incited by
Heterobasidion annosum.
Figure 93. Resin-soaked roots indicative of infection by Heterobasidion annosum; roots often break at
this point during excavation.
Figure 94. Advanced, stringy decay of root tissue of tree infected with Heterobasidion annosum.
Portions of roots closer to the main stem would be resin-soaked.
Basidiocarps, or conks, of the causal fungus may appear on the bark surface at the base of infected trees
or stumps (Figure 95) or may be hidden within the duff layer. Conks may be small and difficult to locate
unless the duff layer at the base of infected trees or stumps is removed. The upper surface of conks is
light reddish brown, the margin is white, and the lower surface has numerous pores that are visible
without the aid of a hand lens. Released spores form a white cast that may be evident on needles in the
duff surrounding a spore-producing conk. Most infected trees do not produce conks.
Figure 95. Basidiocarp (conk) of Heterobasidion annosum on an infected loblolly pine. Note location in
relation to duff layer.
Cause: Annosum root rot is caused by the fungus Heterobasidion annosum (= Fomes annosus).
Suscepts: Annosum root rot has been found on numerous conifers and hardwoods. Of the widely
occurring species, loblolly, slash, shortleaf, eastern white, red, and Scots pine are the most severely
affected. Other species are only slightly less susceptible.
Range and site description: This disease occurs throughout the northern temperate regions of the world
and in some subtropical and tropical areas.
Annosum root rot tends to be more severe on soils that are well drained, sandy to sandy-loam, at least
12 inches (30 cm) deep, and that have a low seasonal water table
In most plantations and stands, this disease becomes a serious problem following some type of
disturbance, especially thinning, Bark beetles may indicate the presence of root rot in pine trees.
Diagnostics: Like many root diseases, the symptoms of this disease are often overlooked during the
initial stages of decline, and, when death occurs, other types of damage are usually thought to be
responsible. This disease is often confused with the effects of littleleaf disease, other root diseases, or
bark beetle infestations.
In many instances, no symptoms are evident until windthrow of living trees occurs.
Littleleaf Disease
Disease description: In its early stages, this disease is characterized by symptoms of nutrient deficiency;
the needles become chlorotic and are slightly shorter than normal. Length of new needles may be only
0.5 inch (1 cm), although normal, healthy needles may be 3 to 5 inches (7 to 13 cm.) long. Shoot growth
is also reduced.
In later stages of the disease, the symptoms become progressively more distinctive. The crown of an
infected tree appears thin and tufted (Figure 96). New needles are discolored and shorter than normal,
and the tree loses all but the new needles near the tips of the branches. Branches in the lower crown die
first, and death progresses upward through the crown. During this time, radial growth is markedly
reduced.
Figure 96. Thin crown of shortleaf pine; caused by invasion of root fungi leading to littleleaf disease.
About three years before death, diseased trees commonly produce abundant crops of small cones.
These stress-crop cones generally contain sterile seed. Trees killed by littleleaf disease can often be
recognized by their persistent crops of undersized cones.
Close examination of the fine feeder-root system reveals dead root tips, lack of mycorrhizal associations,
and cortical root rot.
Stands affected by this disease tend to break up and decline. Affected trees rarely recover from the
effects of the causal complex.
Cause: Littleleaf is caused by the fungus Phytophthora cinnamomi acting in concert with species of the
fungus Pythium and nematodes. The primary fungus has a mobile spore that requires moisture for
dissemination.
Suscepts: Littleleaf disease affects shortleaf pine, and, to a lesser degree, loblolly pine. Other pines,
including Virginia, pitch, slash, and longleaf, are susceptible when site conditions favor attack by the
causal fungi.
Range and site description: Littleleaf disease of shortleaf and other pines is found throughout the
Southeast. Severely affected stands are in Virginia, North Carolina, South Carolina, Georgia, Alabama,
Mississippi, and Tennessee. The disease seldom affects stands younger than twenty years and is most
intense in stands older than forty years.
Littleleaf is severe in stands on clay soils but is seldom a problem in sandy or other well-drained soils.
Disease occurrence is directly related to soil and site characteristics. Wet, eroded, heavy clay soils that
are nitrogen deficient provide the ideal environment for an epidemic of this disease.
Diagnostics: Early symptom expression is difficult to discern from nutrient or water deficiencies. As the
disease progresses, however, the foliage becomes sparse and only tufts of needles remain. Needles
from trees affected with littleleaf disease have a general chlorosis; the yellowing is seldom concentrated
in a specific area. Abundant cone production characterizes later stages of disease development.
Polyporus Tomentosus Root Rot
Disease description: Symptoms of root rot caused by Polyporus tomentosus include basal bark resinosis,
excessive mortality of lower branches, crown thinning with a tufting of foliage at branch ends, reduced
height and diameter increments, and eventual mortality (Figure 97). In addition, infected trees are more
susceptible to windthrow. Infection is most common in trees older than about fifty years. The disease
occurs in both natural stands and plantations.
Figure 97. Yellow needles and thin, dying crowns of sand pine; caused by Polyporus tomentosus.
Buff-colored sporophores of the fungus are produced in autumn around the base of a tree and/or on the
ground directly above infected roots (Figure 98). Infected root wood is usually stained reddish brown;
white pocket rot may be evident.
Figure 98. Polyporus tomentosus fruiting bodies on the duff layer at the base of a sand pine. These
conks retain their yellowish color for several months, then darken with age.
Cause: Polyporus tomentosus is one of the most widespread root inhabiting fungi in the temperate
region of the northern hemisphere.
Suscepts: In North America, this fungus has been reported on all native species of spruce and on most
species of fir, larch, pine, hemlock, Douglas-fir, and juniper.
Range and site description: Polyporus tomentosus is common in coniferous regions of the eastern
United States. It appears to be most prevalent on well-drained, upland glacial tills in the Northeast and
on sandy soils of the Southeast, where soils are typically shallow, thereby restricting rooting depth, and
very acidic, i.e., have a pH of 4 to 5. These sites usually have low nutrient levels and poor moisture
holding capacities. Sites with a thick, moist duff layer also encourage the disease by favoring root
weevils in the Hylobius complex; these weevils inflict feeding wounds that serve as infection courts for
the fungus.
Diagnostics: Early stages of root rot appear as a gradual reduction of height and diameter increments
caused by the progressive decline of roots over a period of years. Infected trees tend to decline slowly, a
condition that could be confused with symptoms induced by other biotic or abiotic agents. Positive
identification of P. tomentosus can be made only by finding sporophores on diseased trees or by
culturing the fungus from infected roots on artificial nutrient media.
Procera Root Disease
Disease description: Procera root disease, also known as white pine root decline, has been a problem,
primarily in Christmas tree plantations. Recent information indicates, however, that this disease may be
widespread in southern pine plantations and may be associated with declining eastern white pine stands
in the southern Appalachian Mountains.
Symptoms are extremely subtle until the final stages of decline and occur within roots, root collars, and
lower boles. Initial symptoms appear in spring with delayed bud break followed by reduced candle
elongation (Figure 99). After a few weeks or months, the needles of eastern white pine wilt and become
pendant. On other pine species, especially those with short needles, the drooping effect is not evident.
Needles change uniformly from deep green to light green to yellow-green to reddish brown and remain
on the tree (Figure 100).
Figure 99. Delayed budbreak and candle elongation (left) due to procera root disease in eastern white
pine.
Figure 100. Reddish brown and wilting needles retained on young eastern white pine infected with
Verticicladiella procera.
During the final year, the foliage may appear tufted, all but the most recent needles drop, or the most
recent needles are shorter than normal. Quite often there is little or no decrease in height until the year
the tree dies.
The bark of limbs and stems becomes spongy to the touch. Resin pockets develop within this tissue, and
resin flows freely if the tissue is punctured. Stem cankering has frequently been noted at the groundline,
as evidenced by a flat area or by sunken bark on one side of the stem.
Infected roots and lower stems are usually resin-soaked, and occasional black streaks run vertically
through the sapwood (Figure 101). Resin may also ooze through the bark and crystallize on the surface,
appearing as white or gray deposits (Figure 102). Weevils and bark beetles may inhabit these tissues and
be mistaken as the primary cause of the problem.
Figure 101. Black stain in wood of eastern white pine infected with Verticicladiella procera. Such stain
may be evident in wood of roots or lower stems.
Figure 102. Gray, crystallized resin deposits on the bark of an eastern white pine; symptomatic of
Verticicladiella procera infection,
Cause: This disease is incited by the fungus Verticicladiella procera. The wet soils and basal resin flow
associated with white pine maladies were described by early investigators as "resinosis disease" and
"wet foot."
Suscepts: Eastern white, Scots, loblolly, red, Virginia, slash, and Austrian pines are the primary hosts of
the causal organism.
Range and site description: This disease is found primarily in the eastern United States. The majority of
affected trees have been observed growing on heavy soils that exhibit poor internal drainage. Extremely
wet weather in the spring may initiate decline.
Procera root disease has been associated with ozone-sensitive white pine in the Blue Ridge Mountains
of Virginia. This disease is also associated with annosum root rot and blue stain diseases.
Diagnostics: Initial symptoms of procera root disease include sudden decline and wilt, uniform fading
and discoloration of the foliage, resin oozing through the bark, and weevil or bark beetle activity. Initial
foliage discoloration (slight chlorosis) may be confused with ozone injury. The final above-ground
symptoms are dry twigs and uniform, rapid browning of the foliage and branches.
Needle Diseases
Symptoms of several foliage diseases of conifers can be easily confused with symptoms of injury caused
by air pollutants. These diseases are foliage blights that primarily affect drought-stressed trees. Other
needle diseases are incited by more aggressive needle-invading fungi. The initial symptoms of these are
easy to confuse, but a careful observer can locate and identify fruiting structures of the biotic causal
agents and recognize the respective symptom patterns to determine the exact cause.
There are three types of needle diseases: needlecasts, needle rusts, and needle blights. In addition,
several canker diseases of young twigs are best evidenced by foliage symptoms, even though the actual
causal agent is present on twigs and stems. A brief description that includes representative examples of
each type of disease follows.
Needlecasts
These diseases are caused by fungi in the class Ascomycetes. With few exceptions, as noted in the
specific disease descriptions, these fungi infect only the needles on the young elongating shoots, but no
symptoms appear until the following winter or early spring. At that time, the infected needles develop
chlorotic spots that rapidly turn tan to reddish brown. Characteristic fruiting structures form on the
needles from midspring to early summer. These structures are usually football-shaped to elongate
brown to black hysterothecia that open with a longitudinal slit. They are easily visible to the naked eye,
especially when the needles are wet. Affected trees shed, or cast, the previous year's needles, leaving
the tree with only a single year's complement of needles.
Lophodermium Needlecast
Disease description: The previous year's needles redden in late winter or early spring; they brown and
fall from the tree in late spring and early summer (Figure 103). In midsummer, black, raised, footballshaped fruiting bodies of the fungus, visible to the naked eye, develop on cast needles. During wet
weather, these fruiting bodies open with a distinct longitudinal split that is easily seen with a hand lens
(Figure 104). Since most spores are released from needles lying on the ground, branches close to the
ground are more severely infected than branches higher in the tree. Severely infected trees retain only
one year's complement of needles. Repeated infection leads to mortality of buds and dieback of lower
branches. Spores are disseminated by wind from midsummer to early fall and infect current-year
needles. The fungus overwinters in these needles, usually causing no visible symptoms until the
following spring, when a yellow spot appears at each point of infection.
Figure 103. Browning and thinning of the bottom crown of Scots pine due to Lophodermium needlecast
disease.
Figure 104. Lophodermium fruiting body
Cause: The fungus Lophodermium seditiosum (= Lophodermium pinastri) causes this disease.
Suscepts: Although most pines may be infected, Scots and Austrian pines are particularly susceptible.
Range and site description: Lophodermium needlecast is found worldwide wherever two and threeneedled pines grow. The causal fungus requires abundant moisture, so the disease frequently develops
first in stands with poor or no weed control, in low-lying areas, or in plantings adjacent to taller trees
that reduce wind-drying of the foliage.
Diagnostics: This disease causes severe defoliation; affected trees hold only current-year needles over
winter. Needles under trees should be examined for the presence of characteristic fruiting bodies.
Infected trees are found most often in areas with poor air drainage.
Hypodernu Needlecast
Disease description: The previous year's needles may redden in late winter and early spring and be cast
in late spring and early summer. More often, however, only scattered red to brownish spots appear on
infected needles. These spots may girdle the needle and kill portions beyond the original point of
infection, while the bases of the needles remain green and healthy. Fruiting bodies may develop in late
spring and early summer within the spots and dead needle tissues. These fruiting bodies are small,
black, football-shaped structures barely visible to the naked eye but readily apparent under a 10x hand
lens. When wet, fruiting structures open with a longitudinal slit. Although the fruiting bodies look
exactly like those of Lophodermium (see Figure 104), the two diseases are distinguishable in the field.
Needles infected by Lophodermium turn brown and fall, whereas many needles infected by Hypoderma
still have healthy green bases and remain attached to the tree. From a distance, Hypoderma needlecast
looks like red band or brown spot needleblight, but it can be distinguished from the latter two diseases
by the fruiting body of the causal fungus. Severely affected trees may lose most of the needles on the
bottom whorls of their branches. The fungus overwinters in new needles, usually inducing no symptoms
until the following spring, when yellow spots appear at each point of infection.
Cause: The fungus Ploioderma lethale (= Hypoderma lethate) causes this disease.
Suscepts: Most hard pines, such as pitch, shortleaf, sand, slash, Table-Mountain, red, pond, loblolly,
Virginia, and Austrian, are susceptible. In Christmas tree plantations, Austrian pine is most commonly
infected.
Range and site description: Hypoderma is found throughout the eastern United States, from New
England to Florida and Louisiana, Like other needlecasts, this fungus requires abundant moisture, and,
therefore, frequently appears first in stands with poor or no weed control or in low-lying areas that are
naturally wet or have poor air drainage. It is also more severe in plantations adjacent to taller trees,
which restrict air flow, or in older trees that are crowded together, thus restricting drying of the foliage.
Diagnostics: Needles remain attached to infected trees. The fungus produces fruiting structures on
infected needles attached to and under the tree. Infected trees are most often found in areas with poor
air drainage.
Cyclaneusma Needlecast
Disease description: Cyclaneusma needlecast can be readily diagnosed in the field because the
symptoms differ significantly from other pine needlecasts. Symptoms develop primarily in the fall on
one-year-old or older needles, which turn yellow with distinct brown bars embedded in Scots pine
needle, showing elongate shape and slit down the middle across the needle surface (Figure 105).
Fruiting bodies of the fungus are white to tan and develop primarily within the brown bars (Figure 106).
Symptomatic needles do not drop immediately but remain hanging in or on the tree for several months.
Symptoms are not concentrated on the lower branches but develop more or less uniformly throughout
the tree.
Figure 105. Casting and barring of older needles caused by Cyclaneusma on Scots pine. Such defoliation
causes thin, see-through crowns.
Figure 106. White fruiting bodies of Cyclaneusma on infected needles of Scots pine. Infected needles
may remain in trees or be found in the duff under the tree.
These symptoms resemble those caused by feeding of the two-spotted pine aphid, Eulachnus agilis.
Needles damaged by aphid feeding, however, do not develop the distinct brown bars and do not bear
fruiting bodies of the fungus.
The fungus overwinters in infected needles, either in or on the tree or on the duff. Severe infection
usually occurs from April to June on the previous year's needles. Infection may occur from July through
December on first- and second-year needles. Infected needles do not develop symptoms until the end of
the second or beginning of the third growing season. Symptoms are most apparent from late September
to early December and from April through June. Severely affected trees retain only one year's
complement of needles and appear thin and ragged.
Cause: The fungus Cyclaneusma minus causes Cyclaneusma needlecast.
Suscepts: Scots and Austrian pines. All trees of commonly grown Scots pine provenances are moderately
to highly susceptible; trees of southern European provenances appear more susceptible than those of
northern European origin.
Range and site description: Cyclaneusma needlecast is found in the northern United States and
southern Canada.
Diagnostics: Cyclaneusma, needlecast of hard pines differs from other needle diseases and air pollutantinduced injury in that the fungus affects needles of any age at any time of the year. Symptoms may
develop from spring through late fall on second-year or older needles, and the characteristic pale, waxy,
tan fruiting structures can be present year round. These structures may be more easily seen if suspect
needles are wrapped in a wet towel for one hour and then viewed with a hand lens.
Needlecast Of True Fir
Disease description: Needlecasts of true firs typically have a two-year disease cycle. The tender first-year
needles are infected in June and July. No symptoms appear until early in the second growing season,
when infected needles turn various shades of red-brown, brown, or tan. During June or July of the
second growing season, asexual fruiting bodies, or pycnidia, develop on the upper surfaces of infected
needles. These pycnidia may be straw-colored to dark brown or black and are usually arranged in long,
straight or sinuous stripes down the middle groove of the needle, or in two bands, one on either side of
the central groove. The discolored needles remain attached to the tree throughout the summer and
winter of the second season. By June or July of the third growing season, the needles are usually
bleached to a light tanish brown or straw color and bear a different type of fruiting body on the
undersides. These fruiting bodies typically are reddish brown to black, depending upon species, and are
footballshaped to elongate. They may extend the entire length of the needle and are usually arranged
along the midvein. The fruiting bodies are very distinct and easily visible to the naked eye. When wet,
they open with a longitudinal slit that is easily seen with a hand lens. Infected needles are normally cast
during the third growing season.
Cause: Several different species of closely related fungi cause needlecasts of the true firs. Some of these
fungi are considered secondary, attacking older needles about to be shed or needles in dense shade;
other species are considered aggressive parasites.
Suscepts: The species infected by the various causal fungi include balsam, Fraser, concolor, grand,
subalpine, and noble fir.
Range and site description: These diseases may be found throughout the ranges of their suscepts. As is
true of other needlecasts, sites that favor high-moisture conditions in the crowns and surrounding
understory species are most conducive to outbreaks of the disease.
Diagnostics: Although infected needles turn brown just before the second growing season, sexual
fruiting structures do not form and needles are not cast until the beginning of the third growing season.
Thus, severely infected firs have one year's complement of healthy green needles and one year's
complement of firmly attached symptomatic brown needles (Figure 107). Sites with poor air drainage,
i.e., those with high air moisture, are conducive to the disease.
Figure 107. Needlecast of true fir with retention of infected needles through the third growing season.
Rhabdocline Needlecast Of Douglas-Fir
Disease description: In late winter or early spring, the previous year's needles develop spots that initially
are yellow and later reddish brown. There is usually a distinct border between healthy and infected
areas on a needle (Figure 108). In late spring, large brown to orange-red fruiting bodies develop in these
spots. Fruiting bodies completely fill the discolored areas, and, when wet, rupture the epidermis,
becoming readily visible to the naked eye. Infected older needles are cast in early summer, leaving trees
with only one year's complement of needles. The disease is most severe on lower branches. Repeated
severe infection may weaken and kill young trees.
Figure 108. Rhabdocline needlecast symptoms on Douglas-fir needles, with orange-red fruiting bodies of
the causal fungus evident.
Cause: The fungi Rhabdocline pseudotsugae and R. weirii cause Rhabdocline needlecast of Douglas-fir.
Suscepts: Douglas-fir is susceptible. Trees of southwestern provenances are more susceptible than those
of the Pacific Northwest.
Range and site description: This disease is found in Douglas-fir stands throughout New England, New
York, Pennsylvania, Minnesota, Wisconsin, Michigan, and western North America. The fungi require
abundant moisture and low temperatures; the optimum temperature range is about 53°F to 59°F (12°C
to 15°C). Thus, the disease develops first in low-lying areas with poor air drainage or on north-facing
slopes. Close spacing also creates favorable microclimates for the fungi.
Diagnostics: From the time of bud break through shoot elongation, the fruiting structures are quite
evident on fallen needles. Toward late season, only current-year needles remain on infected trees. This
disease is present more frequently in low-lying areas with poor air drainage.
Swiss (Phaeocryptopus) Needlecast Of Douglas-Fir
Disease description: In late winter and early spring, one- or two-year-old needles may turn yellow or
appear mottled. These needles gradually turn brown and usually show no distinct margins between
healthy, yellow, or brown areas. Examination of the undersides of these needles with a hand lens in late
spring or early summer reveals two rows of minute, round, black fruiting bodies, one row on each side
of the midrib of the needle (Figure 109). These rows may appear as two rows of "dirt" to the naked eye.
Severely infected trees normally maintain only current-year needles on the lower branches. The disease
progressively intensifies, and may kill, branches. Repeated severe infection may weaken and kill trees.
Figure 109. Swiss needlecast on Douglas-fir needles, with rows of Phaeocryptopus fruiting bodies
appearing as dirt particles to the naked eye.
Cause: The fungus Phaeocryptopus gaumannii (= Adelopus gaumanni) causes Swiss needlecast of
Douglas-fir.
Suscepts: Douglas-fir is the susceptible species.
Range and site description: This disease is found throughout New England, New York, Pennsylvania,
Minnesota, Wisconsin, Michigan, and western North America. The fungus requires abundant moisture;
it usually develops first in stands in low-lying areas that either are naturally moist or have poor air
drainage.
Diagnostics: Trees should be examined for characteristic fruiting structures on the undersides of twoand three-year-old needles. Frequently, only current-year needles remain on the lower branches.
Rhizosphaera Needlecast
Disease description: Between April and early June, infected previous year's needles turn lavender or
purple. Minute, stalked, black, cup-shaped fruiting bodies appear on the needles, each arising from a
stomate. In late May through June the fruiting bodies can be seen with a hand lens as small rows of
"dirt" running lengthwise along the needle (see Figure 109). Infected previous-year needles then drop,
leaving the tree with only current-year needles at the branch tips.
In southeastern Pennsylvania, infection may enter a second cycle on Colorado blue spruce in late
summer and early fall. In late August and September, current-year needles infected earlier that summer
turn purple and bear fruiting bodies. The fruiting bodies release spores, further infecting the currentyear needles. Needles infected in early summer then drop, frequently leaving bare-twigged holes in the
branches of trees (Figure 110).
Figure 110. Hole in a branch of Colorado blue spruce; caused by needlecast incited by Rhizosphaera
kalkhoffii,
Cause: The fungus Rhizosphaera kalkhoffii causes Rhizosphaera needlecast.
Suscepts: In the United States, the fungus attacks spruces, especially Colorado blue spruce.
Range and site description: This disease is found throughout the range of its suscepts. The fungus
requires abundant moisture and rather cool temperatures. Thus, it frequently develops first in stands
within low-lying areas which are naturally moist or which have poor air drainage, or in stands adjacent
to taller trees that reduce wind-drying of the foliage.
Diagnostics: Infected foliage appears to have a lavender or purple coloration. In addition, fruiting
structures on lower needle surfaces and disease occurrence in low-lying sites with poor air drainage are
also diagnostic. Damage by spruce needleminers may easily be confused with the symptoms of this
disease, but the characteristic fruiting structures of Rhizosphaera will not be present.
Needle Rusts
Disease description: Most needle rust fungi cannot spread from conifer to conifer but involve a second,
or alternate, host. Needle rusts are characterized by easily seen yellow, orange, red-brown, or white
Pustules (aecia) filled with powdery spores of the same color (Figure 111). One known exception occurs
on spruce with Chrysomyxa weirii, where the rust fungus appears to be autoecious, and telia are
produced within the pustules (Figure 112).
Figure 111. Aecial fruiting bodies of a needle rust fungus erupting through the surface of infected pine
needles.
Figure 112. Needle rust on spruce as evidenced by orange-colored telial pustules erupting from yellow
infected spots.
Infected needles usually die and are cast by late summer. A few of the rust fungi may persist as
perennial mycelia in infected conifer twigs, invading each successive crop of new needles. In these
cases, the conifer host may develop conspicuous witches' brooms.
Cause: Numerous species of the rust fungi cause needle rust.
Suscepts: All species of pines, spruces, true firs, and Douglas-fir are susceptible to one or more species
of needle rust fungi.
Over twenty species of needle rust fungi are known to attack true firs and alternate to various woody
hosts such as willow and blueberry, herbaceous hosts such as mouse-ear chickweed, or ferns. Fir needle
rusts may occur on current-year or older needles.
About a dozen known species of needle rust fungi that attack spruces alternate primarily to woody
shrubs, such as Labrador tea, bearberry, or brambles. These spruce needle rusts infect only current-year
needles (Figure 112).
About eighteen known species of needle rust fungi that attack pine alternate to woody shrubs such as
gooseberry or to herbaceous plants, particularly species
of composites such as goldenrod and wild aster. Fruiting structures may be found on current-year or
older needles but are most frequently found on second- and third-year needles. The most prominent
conifer species infected include loblolly, Virginia, shortleaf, red, and Scots pine.
Two known species of needle rust fungi that attack Douglas-fir alternate to species of Populus, especially
aspen. They occur only on current-year needles.
Range and site description: In most cases, the rust fungi are distributed wherever the suscepts grow
naturally. Moist, cool weather favors disease development in the spring. Several young loblolly pine
plantations have been reported as severely affected. Needle rust fungi seldom attack large trees; when
they do, they affect only the needles on lower limbs.
Diagnostics: The best feature for diagnosing needle rust on conifers is the presence of the causal fungus,
signaled by a pustule on the needle surface. Infected needles are usually cast from the tree, but mildly
infected needles may remain attached. When needles are handled, the spores of the fungus may be
released from their delicate membrane coverings, producing a cloud of dust and turning one's fingers
orange.
Needle Blights
Needle blights are a diverse group of diseases. Some of their causal organisms can incite explosive
epidemics when environmental conditions are suitable. Since needles of any age may be attacked, signs
and symptoms may occur on firstyear needles as well as on secondyear or older needles.
Brown Spot Needle Blight
Disease description: Symptoms begin to show on current-year needles in July and continue to develop
throughout the summer and fall. Symptoms initially appear on the lower branches but may develop on
much of the tree after two or three years of infection. At first, infected needles appear mottled with
yellow or pale green spots or bands that may have yellowish margins and appear to be resin-soaked
(Figure 113). The centers of these spots then turn brown and the lesions enlarge to girdle the needle. An
infected needle may initially have a spotted midsection, a dead tip, and a healthy green base. The entire
needle eventually dies and turns brown before being cast. Severely affected needles may be cast in the
fall; however, many needles remain hanging in the tree and are cast the following spring and summer.
Repeated infections result in thin, raggedlooking trees, stunting, and even death.
Figure 113. Brown spot needle blight symptoms exhibiting the yellow band, brown spotting, and resin
droplet usually present with this disease.
In the spring, dark brown to black fungus fruiting bodies erupt through the epidermis in the dead
portions of infected needles. These fruiting bodies are barely visible to the naked eye but can be readily
seen with a hand lens. They vary in size and shape, ranging from round "pimples" to elliptical ridges
several times longer than wide. Fruiting bodies of the causal fungus lack the longitudinal slit
characteristic of needlecast fruiting bodies.
Cause: The fungus Scirrhia acicola causes brown spot needle blight.
Suscepts: All pines, including Scots, red, eastern white, ponderosa, jack, Virginia, shortleaf, and longleaf,
are susceptible.
Range and site description: This disease occurs throughout much of the range of its suscepts. It is
particularly important on longleaf pine seedlings in the Southeast. The disease has been of no
importance in New England. Brown spot needle blight is found on all types of sites but favors areas with
poor air drainage because of the associated long periods of moisture.
Diagnostics: The symptoms of this disease are similar to those incited by Dothistroma pini (red band
needle blight). Initially, the observed chlorotic mottle and spotting may appear similar to ozone- or SO2induced injury. A small droplet of resin is commonly associated with each spot. The base of an infected
needle remains green for some time after the rest of the needle dies.
Red Band Needle Blight
Disease description: Symptoms usually do not develop on firstyear needles until fall. At first, infected
needles appear mottled with dark green bands and yellow to tan spots (Figure 114). The mottled areas
soon turn brown to red-brown. Infected needles may have dead tips and healthy green bases; fruiting
bodies develop in these dead spots in the fall. Infected needles are cast in the fall season or may remain
hanging in the tree until the following spring and summer.
Figure 114. Spots and needle necrosis typical of red band needle blight on Austrian pine.
Trees of any age, including seedlings, may be attacked. The entire tree may be affected, but infection is
usually more severe on the lower branches.
In the spring, dark brown to black fungus fruiting bodies erupt through the epidermis within dead
portions of the needles. The fruiting bodies are barely visible to the naked eye but are readily seen with
a hand lens. They vary in size and shape, ranging from small round "pimples" to elliptical ridges several
times longer than wide. Fruiting bodies of the causal fungus lack the longitudinal slit characteristic of the
fruiting bodies of the fungi causing needlecast.
Cause: The fungus Dothistroma pini causes red band needle blight.
Suscepts: While most pines are susceptible, Austrian and ponderosa are very sensitive, Scots and red
pines are resistant. Douglas-fir and European larch that are close to infected pines may become
infected.
Range and site description: Red band needle blight occurs worldwide in the temperate and tropical
highland regions.
Diagnostics: Late-season symptoms of red band needle blight are yellow to tan spots on needles. Spots
may girdle the needle, killing terminal portions. The base of an infected needle usually remains green for
some time after the rest of the needle dies. Examination of symptomatic needles on the tree or in the
duff layer under the tree reveals the fungus fruiting bodies described above,
Twig and Stem Diseases
Little is known about the many twig and stem canker diseases. Most are rather common and are
characterized by a slight constriction in the bark that may or may not be accompanied by resin bleeding.
Diplodia Twig Blight
Disease description: The diplodia twig blight fungus rapidly kills infected young, succulent shoots, usually
before needles fully elongate. Needles on such shoots are often stunted. The fungus can also attack
older shoots through wounds, including those caused by insect injury. Such infection seldom leads to
girdling and death but usually results in the formation of perennial bleeding twig and stem cankers and
twig death (Figure 115). Sometimes only a portion of the young shoot is killed; in such instances, the
junction between diseased and healthy stem tissues is distinctly constricted. The fungus persists for
several years in infected dead needles and cone scales. Fruiting bodies may not appear on these dead
tissues until fall or the following spring. Readily seen under a hand lens, fruiting bodies are embedded in
host tissues; small, black, conical beaks protrude from the surface of these tissues (Figure 116).
Figure 115. Needle death and branch mortality caused by infection of young twigs by Diplodia pinea.
Figure 116. Fruiting bodies (pycnidia) of Diplodia pinea erupting through infected pine needles.
Cause: The fungus Diplodia pinea (= Sphaeropsis ellisii) causes diplodia twig blight.
Suscepts: Douglas-fir and most hard pines, especially Scots, Austrian, red, and ponderosa, are
susceptible. Diplodia twig blight can be very destructive to young Douglas-fir during springs with
abnormally high rainfall. On such diseased Douglas-fir, the elongating shoots suddenly wilt, droop, and
turn brown.
Range and site description: This disease is found in eastern North America, from South Carolina and
Oklahoma northward. The disease is uncommon on pine trees under fifteen years old, except in
abandoned plantations, but may become a problem in younger trees after severe spittlebug
infestations.
Diagnostics: Death and flagging of young shoots and stems, a slight crook, and the presence of black
fruiting bodies on the canker surface aid in diagnosis. A disease that appears similar to diplodia twig
blight is atropellis canker, but in the latter disease the fruiting structure of the causal organism is
somewhat larger.
Cytospora Canker And Twig Dieback
Disease description: Branch dieback is the most common symptom of this disease, with branches in the
lower crown being among those most affected (Figure 117). Needles on cankered branches turn red and
may remain attached for an entire growing season. The base of a dying branch usually has an inch or so
of twig bearing yellowish needles. A faint constriction in the bark may appear within this zone or
between it and the portion bearing healthy needles. If the constriction is not visible to the eye, it
sometimes can be felt by rubbing the fingertips along the bark in this area. Such cankers are not
associated with any visible wounding. Resin flow at the point of cankering along the main stem is usually
in evidence or is deposited on branches and needles below cankered branches (Figure 118).
Figure 117. Branch and lower-to-midcrown mortality of red spruce; caused by Cytospora.
Figure 118. Pitch oozing from a Cytospora-incited canker on the basal portions of spruce limbs.
The causal fungus can cause either a girdling basal-stem canker or a branch and twig dieback. The
fungus is considered to be a weak parasite, attacking only stressed trees. It produces slime spores that
ooze out in yellowish, sticky drops, or, during wet weather, in tendrils (Figure 119).
Figure 119. Spore tendrils of Cytospora emerging through the bark of an infected spruce branch
following a wet period.
Cause: The fungus Cytospora spp. causes Cytospora canker and twig dieback,
Suscepts: Most conifers are susceptible. The girdling basal-stem canker has been observed on Norway,
red and blue spruce, Douglas-fir, and on white, Fraser, and balsam firs.
Range and site description: This disease is found throughout the range of its hosts but is most severe
where trees are suffering from other stresses, such as drought or nutrient deficiencies.
Diagnostics: The disease usually strikes limbs at the base of the tree first and then progresses up the
stem. Pitch ooze at the base of infected limbs is quite common.
Scleroderris, Canker Of Northern Conifers
Disease description: The most characteristic symptom of this disease is an orange-brown coloration of
the bases of needles along an infected shoot (Figure 120). Spores of the causal fungus infect through
buds or needles during midsummer, and the fungus rapidly colonizes the twig and stem tissues. The
following spring, needle bases will discolor and cankers may develop on twigs and the main stem. A
green stain is usually present on freshly cut tissues underneath the canker surface (Figure 121).
Numerous cankers on a young tree will cause mortality; when conditions are proper, a major epidemic
may occur, resulting in the death of large trees over extensive areas (Figure 122). Fruiting structures of
the fungus, i.e., black pycnidia and red-brown apothecia, are produced on the needles, twigs, and canker
surfaces (Figure 123).
Figure 120. Typical dying of the base of needles in red pine following infection of twigs by Sclerodenis
abietina.
Figure 121. Green streaking (stain) in the wood of young stem infected by Scleroderris.
Figure 122. Stand of red pine severely infected by Scleroderris. Note ragged crowns, dieback, and dead
trees.
Figure 123. The reddish brown apothecia fruiting structures of Scleroderris abietina on the bark of an
infected red pine.
Cause: Scleroderris canker is caused by the introduced fungus Gremmeniella abietina (= Scleroderris
lagerbergii). Two strains have been observed in North America: the Lake states and the European
strains. Damage from the European strain is much greater in that it kills large trees by causing extensive
branch mortality.
Suscepts: Scleroderris canker has been reported on red, jack, Scots, pitch, ponderosa, lodgepole,
Virginia, and eastern white pines; on black, white, and Norway spruce; and on Douglas-fir and larch.
Major epidemics have been observed in red, jack, and Scots pine plantations.
Range and site description: This disease occurs throughout the Lake states and into Vermont and New
York. The fungus is known as a cool- temperature organism and is favored by conditions in low-lying or
frost pocket sites. The potential for spread from its current range is great.
Diagnostics: The most useful diagnostic symptom involves the initial coloration and death of needle
bases. Infected needles fall from a slight touch, and bud and branch tips will be brown. Small cankers on
twigs and a green coloration of tissues under the bark are also diagnostic. The presence of this type of
disease in low-lying areas may also assist in correct identification.
Eastern Dwarf Mistletoe
Disease description: The most prominent symptom of eastern dwarf mistletoe infection in spruce is the
witches' broom, a proliferation of host tissues that produces a slight swelling of the branch, followed by
the formation of a compact, bushy mass of branches and twigs that tend to have a positive phototropic
growth habit. Witches' brooms can vary in size from a few small twigs to compact brooms measuring up
to about 120 inches (3 m) in diameter (Figure 124). Swellings on main stems may be a result of old, but
still active, bole infections (Figure 125).
Figure 124. Witches' broom on red spruce, indicative of infection by the eastern dwarf mistletoe plant,
Arceuthobium Pusillum.
Figure 125. Swelling of main stem of red spruce due to an old, but continuing, bole infection.
The rootlike system of the dwarf mistletoe plant grows within host branches and eventually gives rise to
shiny, small, separate male and female aerial shoots (0.5 to 1.5 inches or 1 to 4 cm long), with greenish
brown, scalelike leaves (Figures 126, 127). These aerial shoots die and fall off soon after pollen
production in spring and seed dispersal in fall, leaving basal cups on host branches. The basal cups can
be easily seen with a hand lens, and, along with the aerial shoots, serve as a sign of dwarf mistletoe
presence.
Figure 126. Arceuthobium pusillum plants, showing growth habit on branches of red spruce.
Figure 127. Close-up of mistletoe plant, of showing its size relative to the needles its host plant, red
spruce.
Within stands, irregular, circular patches of infected trees can be observed. Infected trees have witches'
brooms, swollen branches, spike (dead) tops, reduced growth, and poor wood quality. In addition, trees
are weakened and predisposed to infestation by other pests, such as fungi and insects. Mistletoe
infested stands usually become poorly stocked. They also tend to be more open, so that infected living
trees, especially those with large witches' brooms, are more susceptible to windthrow.
Cause: The parasitic plant Arceuthobium pusillum is the eastern dwarf mistletoe organism.
Suscepts: White, red, and black spruce are considered to be the principal hosts.
Range and site description: Eastern dwarf mistletoe is found on black, red, or white spruce growing in
pure and mixed stands in eastern North America.
Black spruce usually grows in pure, even-aged stands in cool sphagnum bogs with deep, wet, organic
soils. White spruce grows in extensive pure stands in its northern range. It prefers moist loam or alluvial
soils and is typically found along stream banks, lake shores, and adjacent areas. White spruce along the
coastal areas of Maine is heavily infected with eastern dwarf mistletoe. Red spruce has recently been
found infected in mixed stands in several New England states.
Diagnostics: The presence of witches' brooms is the best diagnostic tool; however, not all brooming in
spruce results from infection by dwarf mistletoe. Some brooms are thought to be caused by genetic
mutation, others by the spruce broom rust fungus, and still others may be caused by repeated snow,
wind, or ice breakage of leaders. No other diseases mimic the symptoms associated with eastern dwarf
mistletoe infection. However, since the causal organism is so small and difficult to detect until brooms
are established, early symptoms may be confused with other decline situations. A tufting of small
branches and foliage has been reported on spruce showing progressive symptoms of dieback and
decline. The cause of these symptoms is unknown.
White Pine Blister Rust
Disease description: The blister rust fungus infects pine needles in late summer or early fall. The fungus
grows through the needle and twig into larger branches or the main stem of the tree, where it grows
throughout the host cambium and bark. During the second growing season, a slightly sunken, reddish
brown area may appear. At the end of the third growing season, tissues above the cankered area may
swell. Two to three years after initial infection, the blister rust fungus produces spores that can be
identified on the bark surface by ooze which remains shiny after drying. The fungus continues to
colonize adjacent tissues each year, and the cankered area enlarges. One year after the first spore stage,
a second spore stage produces bright yellow-orange pustules directly on the canker surface (Figure 128).
These spores are windblown and often appear as a dust cloud emitted from a tree that has been blown
or shaken by the wind. Second-stage spores infect currant or gooseberry, the alternate hosts.
Figure 128. Yellow-orange pustules (aecia) erupting through the bark of eastern white pine infected by
Cronatium ribicola, the blister rust fungus.
Cankers on infected pines eventually girdle branches or main stems, resulting in dead branches or dead
treetops. While both small and large trees may die from infection, the ability of the fungus to kill a tree
depends upon the diameter of infected stems and the growth rate of the fungus. In many instances,
hundreds of cankers have been found on a single tree. Tops of trees with trunk cankers usually turn pale
green or yellow several months before dying (Figure 129). Old cankers are characterized by abundant
pitch flow and the remnants of the earlier spore stages.
Figure 129. Eastern white pine tree declining from blister rust infection, showing off-color of crown that
will be followed by crown death above the cankered area.
Cause: The fungus Cronartium ribicola causes blister rust of white pine.
Suscepts: All five-needle (white) pines are susceptible to some extent to the attack of the causal fungus.
No commercially important white pine species are resistant to infection. In the past, the disease has
been particularly damaging to eastern white pine. The alternate host is Ribes spp. (wild currant) or
Grossularia spp. (gooseberry).
Range and site description: Blister rust of white pine affects stands in the East from Maine to North
Carolina and westward to Minnesota in a band across the northern states.
Diagnostics: Stem and branch cankers are evident below foliage areas that have died or become
chlorotic. Fruiting bodies of the causal fungus may be present on the cankered surface in late spring or
early summer. Trees with dead tops should be closely examined for main stem cankers.
Comandra Blister Rust
Disease description: Comandra blister rust is very similar in symptomatology and disease cycle to white
pine blister rust. Following infection of young shoots, the causal fungus becomes established in the inner
bark and young wood tissues. Fruiting of the pycnial stage may occur one to three years later, with
typical shiny ooze in evidence on swollen, spindle-shaped areas of stems and twigs. Later in the disease
cycle, the bright orange, rust- colored aecial spore stage is produced on infected bark surfaces (Figure
130). Developing cankers are rough-surfaced and usually bleed resin profusely. Yellowing and necrosis of
foliage occurs distal to the cankers, with associated twig, branch, and main stem death following girdling
of tissues. Spiketops will occur on larger trees.
Figure 130. The aecial stage of Cronartium comandrae on a limb of loblolly pine.
Cause: The fungus Cronartium comandrae causes comandra blister rust.
Suscepts: The major eastern forest trees susceptible to this fungus include loblolly, jack, pitch, Scots,
shortleaf, Table-Mountain, and Virginia pines. The disease is economically important on loblolly pine.
Young pine plantations less than ten years old are most severely affected. The alternate host is the falsetoad-flax.
Range and site description: This disease is primarily found in the central portions of the eastern United
States, i.e., in Tennessee, Kentucky, and North and South Carolina. However, the disease may occur in
most eastern states wherever the alternate host is found.
Diagnostics: Small swellings on twigs and the presence of fruiting stages of the rust fungus are most
helpful in diagnosis. Cankers and resin flow may also indicate the presence of the disease.
Fusiform Rust
Disease description: Fusiform rust is characterized by spindleshaped galls on branches or the main stem
of pine. Galls are elongate, often with deep fissures, and seldom show a pronounced ridge between
healthy and infected tissues. In early spring, pustules containing bright orange spores form on the galls,
making them very conspicuous (Figure 131). Many galls may be present on one tree. Galls on the main
stem of young trees may cause breakage or may girdle the stem.
Figure 131. Spindle-shaped Fusiform rust gall on loblolly pine stem, showing bright yellow aecial spore
stage of the causal fungus.
Oak serves as the alternate host for this rust fungus, which produces fine, brown, hairlike projections on
the lower surface of infected leaves. Severely infected leaves may exhibit chlorotic spots and some
distortion, but oak leaves usually remain symptomless.
Suscepts: Loblolly and slash pine are highly susceptible to infection. Longleaf pine is somewhat resistant,
and shortleaf and Virginia pine are considered immune. Alternate hosts include water, willow, and laurel
oaks as being most susceptible, with other red and black oaks being less favorable hosts. White oaks are
rarely infected.
Range and site description: Fusiform rust has been found from Maryland to Florida and Texas. Sites that
tend to have high relative humidity and warm temperatures for extended time periods favor
development of Fusiform rust epidemics.
Cause: The fungus Cronartium quercuum f. sp. fusiforme causes Fusiform rust.
Diagnostics: Spindle-shaped galls on stems and/or branches are characteristic symptoms. Main stem
breakage often occurs at the point of gall development. Fusiform rust has been known to decimate
entire stands.
Pine-Oak Rust
Disease description: Pine-oak (also known as eastern gall) rust is characterized by brain-shaped galls on
the main stem of the pine hosts (Figure 132). Hundreds of galls have been observed on a single tree.
Usually galls are quite distinct from the main branch, and a collar of bark separates diseased from
healthy tissue. Severe infection may lead to tree deformity, reduced growth, breakage at the point of
gall formation, and death. On larger stems, galls may serve as the entry point for decay fungi. During
spring, the bright orange spores of the fungus make the galls very conspicuous.
Figure 132. Brain-shaped pine-oak rust gall on Virginia pine branch with the aecial stage of the causal
fungus in evidence.
Oak serves as the alternate host. Oak leaves seldom exhibit symptoms of infection unless severely
infected, and then only a mild chlorosis or chlorotic spotting may occur. Brown, hairlike projections of
the fungus on the lower leaf surface are normally the only sign of infection.
Cause: The fungus Cronartium quercuum f. sp. banksianae causes pine-oak rust.
Suscepts: Many species of pine and oak are susceptible to infection by the various stages of this rust
fungus. Pine hosts include Virginia and Scots pine. Red, black, scarlet, and pin oaks are considered the
most susceptible. Infection of white oak, American chestnut, and chinkapin has been noted in the
southeastern United States.
Range and site description: This disease is found throughout the eastern United States and has been
considered a serious problem in nurseries in the Great Lakes states. Many jack pine plantations have
been severely attacked and rendered useless for timber production.
Diagnostics: Round galls on stems and branches are characteristic symptoms. Severely infected trees
may be deformed and may suffer breakage at the gall area.
Abiotic Stresses Of Hardwoods And Conifers
The foliage of an entire tree often turns brown or off-color with no obvious signs of causal agents. Closer
examination of roots, stems, or foliage for other symptoms may yield little additional information.
Problems of this nature may be due to local weather conditions, including drought, winter drying, or ice.
In addition, nutrient imbalances can induce locally mild to severe symptoms.
Temperature and Moisture Injury
Winter Injury (Drying)
Disease description: Winter injury is most prominent on conifers, and, because of its many possible
symptoms, is usually hard to recognize. Symptoms of winter drying do not appear until the following
spring and may include marginal scorch, tipburn of needles, mottling and death of leaves, and various
amounts of leaf fall (Figures 133, 134). Dead leaves are a uniform tan, and the afflicted leaves and twigs
that remain on the tree are very dry and brittle. Tip dieback may affect some hardwood species and is
most likely due to early spring frosts that kill terminal buds and twigs; when new growth begins, affected
plants appear to be tufted.
Figure 133. Winter injury (drying) on red spruce trees, showing injury to previous years' foliage and
defoliation.
Figure 134. Close-up of winter injury on red spruce branch with orange coloration and shoot death
evident.
Cause: Damage is most likely to occur on warm winter days that have been preceded by a prolonged
period of very low temperatures. Under such conditions, soil water is frozen and is no longer available to
the plant, and/or the water present in the plant stem is frozen and blocks the upward movement of
water to the leaves. During periods of warm weather when a slight wind is accompanied by low relative
humidity, the tissues of leaves, stems, and buds begin to lose water to the air. This water cannot be
replaced due to the frozen soil and stem water. The extent of leaf damage, i.e., marginal scorch or death
of the entire leaf, and survival of the entire plant depend upon the length of exposure to such
conditions. Winter drying is not the same as blackening of foliage due to late spring frosts.
Suscepts: Any species of plant is sensitive to winter drying when exposed for a sufficient length of time.
Plants that retain their leaves over winter, however, are more likely to be injured than are deciduous
species.
Conifers of all types are particularly susceptible to winter drying. Portions of the plants that lie beneath
the snow cover are usually not affected. Large numbers of trees, especially loblolly pine, have been
damaged during recent winters characterized by little snow cover and subfreezing temperatures.
Range and site description: Winter drying is most common where species are at the northern edge of
their range, but it may also damage species of plants native to an area well within their range. Trees
exposed to high winds during severe cold, such as those found on the edges of stands adjacent to large
expanses of open terrain, are sensitive to winter injury.
Diagnostics: Winter drying is most severe on conifers. A chlorotic mottle or uniform yellowing of tissue
may exist in early spring; a uniform browning or tan coloration follows (Figure 135). Injury is often found
on the southwest facing side of exposed trees, i.e., the side facing the prevailing winds. Many root
diseases caused by biotic pathogens produce symptoms similar to those that result from winter drying.
Figure 135. Close-up of winter injury on red spruce needles.
Frost
Late spring or early fall frost injures sensitive plant tissues. Late spring frosts are the most damaging,
since the young foliage is succulent at that time of year. Diagnosis is easy, as the frozen tissues turn
blackish brown (Figures 136, 137). Mild freezes or even cool temperatures may cause slight tissue
collapse and/or chlorosis that may resemble air pollution-induced symptoms, such as severe SO2 injury.
Weather records and personal observations can assist in identifying injury caused by late spring frosts.
Initiated by early fall frosts, premature autumn coloration and leaf drop are common in several species
of plants. Green foliage may drop from the tree, and remaining foliage may have light brown margins.
Figure 136. Frost injury on current-season needles of Scots pine, following a sudden temperature drop in
the late summer.
Figure 137. Frost injury on new growth of a dogwood, resulting in blackened leaf tissues.
High Temperature
Periods of extremely high temperature combined with windy conditions can injure many tree species,
even when adequate moisture is available in the soil Injury symptoms appear at the periphery of crowns
and include a marginal scorch of leaf tissues, with a fairly sharp line between affected and healthy areas.
Symptoms may resemble those induced by fluorides.
During spring, periods of cool, wet weather that are followed by sudden extremely high temperatures
may increase the extent of heat injury. High temperatures may also injure plants growing in shaded
areas that are suddenly exposed to direct sunlight.
Drought
The symptoms of prolonged drought are easily recognizable; awareness of recent drought at a particular
site will assist in diagnosis. Typical wilt symptoms, including drooping or cupped leaves, pendant
needles, and browned terminal portions of foliage, may be evident, On dry sites during particularly long,
dry periods, wilting symptoms may appear in late afternoon. Crowns may look thinned due to the
cupping and rolling of leaves. In severe instances, defoliation and other dieback and decline symptoms
may follow. (See section on diebacks and declines.)
Excessive Water
Excessive amounts of water may injure trees. Symptoms are usually associated with man-made changes
in grade levels around logging sites or adjacent to new highways where streams have been blocked.
Symptoms include dwarfing of leaves, general chlorosis of all foliage, and dieback. Affected plants may
die gradually, and the cause of death can be readily identified by examining drainage conditions in the
area.
Chemical Injuries
Salt Spray Injury (Highways And Inland Of Oceans)
Disease description: The accumulation of salt on or within plants often causes severe injury. This injury
may occur on plants growing where deicing salts are used or up to tens of miles inland from ocean
sources. In long-term impact areas, tree dieback, decline, and death have been noted to occur. Uptake
occurs through direct foliar applications of wind-driven sprays or through root absorption of salts
accumulated in sods. Due to their year-round foliage, conifers may have symptomatic foliage during
winter months. Terminal portions of needles turn red-brown then become darker brown and very brittle
(Figure 138); wind breakage of dead needle portions is common. Hardwood foliage shows a marginal
chlorosis, followed quickly by marginal necrosis and defoliation (Figure 139). Premature fall coloration
can also be a symptom of salt injury. Bud, twig, branch, and tree death occur in both conifers and
hardwoods.
Figure 138. Salt spray injury on eastern white pine located next to road surface treated with deicing
salts.
Figure 139. Marginal scorch of basswood leaves due to toxic accumulations following uptake of deicing
salts.
Cause: Salts like NaCl and CaCl2 in aerosol form, roadway application of deicing salts, natural saltwaters,
and cooling tower spray drift from use of saline waters at large power plants have all been shown as
important sources.
Suscepts: Most major forest tree and understory tree species are sensitive to salt accumulations and
sprays. Notable among these are sugar maples adjacent to roads throughout New England and eastern
white pine at distances in excess of 300 yards (300 meters) downwind of heavily travelled highways.
Loblolly and other coastal species have been injured by wind-driven sea spray up to distances of 12 to 18
miles (20 to 30 km) inland.
Range and site description: Saltspray injury can occur almost anywhere salts or sea spray exist. Low-lying
areas adjacent to roads allow accumulation for eventual root uptake, Damage is often most severe on
trees located downwind of major highways.
Diagnostics: Observing the location of injured trees is most helpful in diagnosis. Symptoms resemble
those of abiotic stresses, including acute air pollutant injury. Weather patterns like recent hurricanes
should also be checked when injury is inland of ocean sources.
Pesticide Spray Drift
Herbicide application for control of undesirable vegetation is a fairly common forest management
practice during site preparation or tree release operations, Herbicides are also used to control brush
within and along power lines and various pipeline rights-of-way. Such chemicals are also used along
highways and rail lines and on expanses like golf courses, agricultural fields, and similar areas to control
competitive vegetation.
Large acreages have also been sprayed with various insecticides in control efforts aimed primarily at
defoliating types of insects like the gypsy moth and spruce budworm. Fungicides or other diseasecontrol chemicals are seldom applied to forest trees, with the noted exception of needle disease-control
programs on Christmas tree plantations.
Pesticide application practices occasionally result in injury to non-target vegetation through drift of the
chemical, improper conditions for application, or improper dosage application. Herbicidal drift is the
major cause of such induced injuries under forest conditions.
On broadleaf species, symptoms may include chlorotic or necrotic spotting, marginal scorch, leaf
cupping and curling (Figure 140), bud death, tree dieback, decline, and perhaps mortality. Injury to
conifers may include similar spotting patterns, but banding, tip necrosis, and curling of new shoots may
also occur (Figure 141). A pattern of injury to nontargeted vegetation may be evident from the actual
application of pesticide application, through a progression of symptoms, to a lessening and eventual
disappearance of symptoms. Knowledge of direct or nearby pesticide applications, amounts, conditions,
times of application, and actual chemical(s) used will assist in proper diagnosis. Tissue analysis may be
necessary to confirm and properly identify such chemical injuries.
Figure 140. Herbicide injury to red maple leaves. Note curled, twisted, and elongated leaf deformation.
Figure 141. Herbicide injury to Colorado blue spruce, showing tip necrosis of newest needles.
Nutrient Imbalances
Much is known about the symptoms associated with the shortage or excess of nutrient supply to plants.
The effect of either extreme is, however, sometimes difficult to diagnose and may require chemical tests
of soil and plant tissue.
Symptoms of a specific nutrient deficiency may appear on all parts of a tree but are most common on
foliage. The coloration exhibited by the foliage is often the best means of determining the element
involved. Lists of nutrient disorders are available. Some nutrientimbalance symptoms are similar to
those induced by air pollutants.
Unfavorable soil pH may cause mineral imbalances in the soil solution. These imbalances are usually
manifested in the foliage as nutrient excesses or deficiencies. Low or high pH, for example, may lead to
the release of minerals like aluminum that become toxic to the plant or to the immobilization of
minerals like iron or phosphorus that are essential for plant growth. In the eastern United States, low
soil pH is the most common cause of foliage yellowing in some species, resulting in stunting, loss of
leaves, and sometimes death. Soil analysis should be conducted where symptoms are present, and, if
possible, a comparison should be made to optimum nutrient levels for the specific species involved.
Forest Tree Insects
Numerous insect species cause injury to trees in the temperate forests of the eastern United States.
Insects attack all parts of trees, including foliage, shoots, cones, seeds, stems, and roots. Injury may be
negligible or present as scarcely noticeable feeding on leaves, or it may be catastrophic, as when
defoliation of millions of acres leads to decline and death of trees, or when the girdling activities of
feeding bark beetles lead to extensive mortality. Only selected examples of insect injury are included in
this manual; many other species are found in the field. For diagnostic purposes, the observer should at
least be able to identify the feeding groups of these other species, and, in most cases, to separate
insect-induced injury from injury caused by other agents. In many instances, the insect being reviewed
has not been associated with specific sites; however, its general range has been presented.
This part of the manual is divided into two major sections: Hardwood Insects and Conifer Insects. In
some instances, the same species of insect attacks both hardwood and conifer hosts. Each major section
is further divided into discussions based on feeding groups.
Leaf-eating insects (defoliators) may be divided into three subgroups: chewers, leafminers, and
skeletonizers, depending on the location and kind of feeding activity. Chewers are insects that consume
entire leaves or large portions of leaves, frequently including vascular tissues. Especially during the early
in stars, some species eat only holes in individual leaves, making them appear as if they had been
blasted with a shotgun. This kind of leafleating is known as shothole feeding. As larvae grow, they
consume larger portions, often beginning at leaf edges and eventually removing entire leaves.
Leafminers live between the epidermal layers of leaves, sometimes consuming vascular tissues as well.
Skeletonizers consume leaf tissue, often from the lower side of the leaf, leaving only the upper
epidermis or vascular tissues.
Sucking insects have sucking rather than biting and chewing mouthparts. These species insert their
mouthparts into plant tissues and draw nutrients and fluids from their host. Noningested plant tissue is
frequently discolored, misshapen, or has galls as a result of excessive tissue growth.
Meristematic insects may attack any of the growing tissues of a tree, including shoots, twigs, cones,
seeds, roots, or the phloem-cambium areas. Depending on the tissues involved and the intensity of the
attack, damage symptoms may be local, i.e., limited to single cones or seeds, or extensive, e.g., a bark
beetle attack in the bole that girdles and kills the whole tree.
Wood and wood-boring insects are common, especially as secondary invaders, but their symptoms are
not likely to be confused with air pollution damage, so they are not included as a separate group in this
manual.
Hardwood Insects
Because the majority of important insect pests of hardwoods are leaf-eaters, such insects are
emphasized in this manual. A few examples of insects with sucking mouthparts and a meristem feeder
are also included for reference.
Leaf-eating Insects (Defoliators)
Gypsy Moth
Description of injury: Eggs hatch in the spring at about the time of budbreak and early leaf expansion.
Young, black, hairy larvae about 1/8 to 1/4 inch (3 to 6 mm.) long crawl up to the tops of trees, spin
down on silken threads, and are blown by the wind from tree to tree or over even greater distances.
Once settled on a suitable host, larvae begin to feed. Early feeding when leaves are expanding removes
small pieces of leaf tissue (Figure 142); this is called shothole feeding. By late spring, large pieces of leaf
are consumed and leaves may be severed at the petiole, giving the appearance of premature leaf fall.
Figure 142. Defoliation caused by gypsy moth larval feeding on chestnut oak. Shotholes are caused by
young larvae; larger holes and edge feeding are caused by larger larvae.
Trees may be partially (Figure 143) or completely defoliated. From a distance, light defoliation may
make the tree appear unthrifty; closer examination reveals missing portions of leaves or needles. For
many hardwoods, heavy defoliation (foliage loss exceeding 60 percent) triggers refoliation during
midsummer; a single complete defoliation frequently kills coniferous hosts.
Figure 143. Moderate defoliation of oak tree canopy; caused by gypsy moth feeding.
Hosts: The insect does especially well on white and chestnut oaks. Other common hosts include red and
black oaks, aspens, gray, white, and river birches, willows, and especially for the older larvae, beech,
hemlock, Douglas-fir, and all species of pines and spruces. During population outbreaks, all forest tree
species except yellow-poplar and ash may be partially or entirely consumed,
Range and site description: The gypsy moth occurs over large areas in the northeastern United States.
Isolated infestations have been discovered in several midwestern, southern, and western states.
Trees growing under all sorts of conditions may be attacked trees on ridges, slopes, bottomlands, in
urban environments and forests, on good or poor sites, in pure stands, or in mixed forests.
Insect: The gypsy moth, Lymantria dispar, overwinters in the egg stage. Single egg masses may range
from the size of a dime to larger than a half dollar; egg masses are circular to oval and are buff-colored
(Figure 144) masses.
Figure 144. Adult female gypsy moth laying a mass of eggs in a bark crevice on oak. Egg masses may be
numerous, and their evidence may remain for a second season.
Diagnostics: Except for partially consumed and then abandoned needles that may discolor, feeding does
not normally cause discoloration of foliage left on trees. There is little chance of confusing defoliation
with disease or air-pollution damage if individual leaves are examined. During the fall, winter, or early
spring, look for the egg masses and other signs of attack by agents associated with dieback and decline
diseases, may be laid almost anywhere but are most commonly seen on boles of trees, especially those
with rough or fissured bark. Undersides of large branches in the lower crown are frequently used for egg
deposition. Fully grown larvae are from 1 to 3 inches (2 to 8 cm) long, dark gray in color, and have five
pairs of blue tubercles (dots) and six pairs of brick red tubercles on the dorsum, or upper side (Figures
145, 146). From mid-June to late July, brown pupae may be found; the pupal stage lasts ten to fourteen
days. Pupae are loosely attached to the substrate, often under leaves or bark flaps, or in hollows of trees
or fissures in the bark. Adult males, which are fairly strong daytime fliers, are brownish with dark wavy
bands across each forewing; nonflying females are larger, off-white, and, like males, have wavy bands
and marginal dark spots on their forewings (Figure 144).
Figure 145. Fully grown gypsy moth larva, showing five pairs of blue tubercles followed by six pairs of
brick red tubercles on the dorsum.
Figure 146. Large gypsy moth larvae, showing red color phase typical of heavy infestations (left) and gray
color phase typical of light to moderate infestations (right).
Oak Leafroller
Description of injury: Larvae hatching before budbreak enter and mine leaf buds, destroying a number
of leaves; those hatching later consume emerging leaf tissue, normally from the edges of leaves. Trees
under attack may appear to have thin crowns if leafroller populations are not particularly heavy; when
populations are heavier, most leaves may be damaged (Figure 147). Close observation reveals consumed
portions of leaves, and, especially from early summer onward, many rolled leaves (Figure 148). These
rolled leaves will often contain larvae, or, later on, pupae or cast pupal skins.
Figure 147. Defoliation of oak species caused by the oak leafroller, leading to thin crowns, dieback, and
decline.
Figure 148. Leaf showing skeletonizing and rolling by oak leafroller on red oak.
Early-season defoliation may trigger refoliation of host trees that lose more than 60 percent of their
foliage. Heavy defoliation for two or three successive years causes tree mortality. Because the energy
reserves of the trees are so depleted, stump sprouts or root sprouts rarely occur.
Hosts: While oak leafroller larvae favor oaks, they also feed on maple, witch-hazel, and apple, especially
during population outbreaks. The oak leafroller may occasionally cause extensive defoliation over large
areas of forest, especially in forests with large proportions of red and white oaks.
Range and site description: Outbreaks normally occur in mature to overmature forests and have been
recorded in some of the northeastern and northern midwestern states. During the last several decades,
severe outbreaks have been reported in Michigan, Pennsylvania, and New York. Pennsylvania suffered
extensive tree mortality during the late 1960s and early 1970s, probably because a prolonged drought
intensified the effects of defoliation. Some of the heaviest defoliation has been recorded on trees on
some of the better bottomland sites.
Insect: The oak leafroller, Archips semiferanus, overwinters in the egg stage. Egg masses are closely
appressed to the bark of the tree (Figure 149). Numbers of egg masses are concentrated on the lower
bole and in the lower portion of the crown. Egg masses may also be found on some of the larger, lower
branches.
Figure 149. Closely appressed egg masses of the oak leafroller, Archips semiferanus, on the bark of oak.
Topmost egg mass shows exit holes from hatched larva
At about the time of foliage flush, newly hatched larvae are less than 1/8 inch (3 mm) long. Through a
series of molts, they grow to approximately 3/4 inch (2 cm) long. They are yellowish green and have a
dark head capsule (Figure 150). Larvae continue to feed on the succulent young and expanding leaves
until mid to late June, at which time they pupate in rolled leaves, bark fissures, or other sheltered
places. New pupae are light brown and darken with age. Adults are 1/2 inch (1 cm) long, reddish brown
moths.
Figure 150. Larvae of the oak leafroller feeding on young, expanding leaves of oak.
Diagnostics: Close examination of foliage reveals that pieces of leaf have been removed. Numbers of
rolled leaves, cast larval skins, pupal cases, and hatched or unhatched egg masses on the bark are easily
seen, particularly in moderate to heavy infestations.
Forest Tent Caterpillar
Description of injury: Egg masses of the forest tent caterpillar may be observed on twigs of the hosts
from midsummer through to the following spring (Figure 151), Young larvae sometimes skeletonize
leaves, whereas older larvae typically consume entire leaves. Defoliated forests appear silvery gray from
a distance or from the air. Early feeding by larvae is done mainly in groups; larger larvae feed singly. In
spite of its common name, this insect does not form tents. Diebacks and declines may follow defoliation.
Figure 151. Egg masses of the forest tent caterpillar deposited along a twig of an unidentified host
species.
Hosts: Forest tent caterpillars attack many different kinds of hardwoods, but they prefer trembling
(quaking) aspen, sugar maple, blackgum, tupelo, and sweetgum; various species of oaks are commonly
attacked in the South.
Range and site description: This insect thrives throughout most of the United States and Canada
wherever suitable hosts are present. Trees on bottomlands and along water-ways are commonly
attacked.
Insect: Fully grown larvae of Malacosoma disstria, the forest tent caterpillar, may be 2 to 3 inches (5 to 8
cm) long and have light blue heads with black mottling. Each abdominal segment has a brownish yellow,
keyhole-shaped spot in the middle of the upper side (Figure 152). Larvae are bluish gray with a gray
lateral stripe running the length of the body.
Figure 152. Larva of the forest tent caterpillar, Malacosoma disstria, showing the characteristic keyhole
pattern on the dorsal side.
Diagnostics: Larvae do not form tents but rather lay down silken trails or mats on foliage and tree bark.
Pupae are contained in pale yellowish cocoons, often in folded leaves, bark fissures, or other protected
places. Close examination reveals portions of leaves removed or entire leaves missing.
Fall Cankerworm
Description of injury: In early spring, shortly after budbreak, young larvae of fall cankerworm feed as
skeletonizers or shothole feeders (Figure 153), primarily in the upper edges of the crown. As larvae
grow, they consume entire leaves, sometimes leaving main ribs, and then move down into the crown
after they have consumed the tops of the trees. Feeding is normally completed by mid-June.
Figure 153. Feeding injury caused by fall cankerworm on sugar maple.
Outbreaks of fall cankerworm may cause extensive defoliation over large areas of forested land. With
repeated successive years of defoliation, trees weaken, decline, and may die. Large numbers of larvae
frequently can be observed moving across the ground, seeking new sources of food after they have
defoliated a tree.
Hosts: This insect is found on almost all hardwood species in eastern North America but prefers elm,
basswood, red, silver, and sugar maple, red oak, apple, hickory, ash, beech, and boxelder.
Range and site description: Fall cankerworm occurs throughout the eastern United States as far south as
Georgia and west to Missouri and Montana. In southern Canada, it occurs in the Maritime Provinces and
west to Alberta.
Insect: The fall cankerworm, Alsophila pometaria, has full-grown larvae about 1 inch (2 to 3 cm) long.
The head and anal shield vary from light green to almost black; longitudinal stripes run the length of the
body (Figure 154). Larvae are loopers, which move by drawing the posterior portion of their abdomen
up behind the thorax while looping their middle portion above the surface. Larvae have a single pair of
rudimentary prolegs and two pairs of normal prolegs.
Figure 154. Larva of the fall cankerworm, Alsophila pometaria.
Diagnostics: Look for early feeding in the upper periphery of crowns of suitable hosts, followed by
heavier feeding that progresses down the crown. Larvae are easily seen until pupation, which occurs in
cocoons in the ground. As noted earlier, these are typical looper larvae, which move inchworm fashion.
Saddled Prominent
Description of injury: During the first three stadia, larvae of the saddled prominent feed as skeletonizers,
usually on the undersides of leaves. During the remaining larval stadia, the insects consume foliage from
the edges of leaves, devouring all of the tissues. During outbreaks, the saddled prominent may heavily
defohate entire trees over extensive areas of forested land (Figure 155). Following a single defoliation,
some dieback may be seen in the smaller twigs in the upper portion of the crown; successive years of
defoliation reduce annual growth and may kill some trees.
Figure 155. Varying degrees of defoliation caused by the saddled prominent in a mixed hardwood stand.
Hosts: Beech, yellow birch, and sugar maple are preferred, but more than twenty other hardwoods have
been recorded as hosts, especially in outbreak conditions.
Range and site description: The saddled prominent is found throughout the eastern United States and
southeastern Canada.
Insect: Young larvae of the saddled prominent, Heterocampa guttivitta, possess a pair of fleshy, antlerlike horns on the first thoracic segment and are dark red to black. Older larvae have a brownish purple
"saddle" marking dorsally on the first several abdominal segments (Figure 156). Full-grown larvae are
about 1¼ inches (3 cm) long and have a flattened, backward-angled head capsule.
Figure 156. Larva of the saddled prominent, showing its characteristic saddle marking on the dorsum.
Diagnostics: Larvae can be found feeding on leaves from mid-June through mid-August. Obvious injuries
include removal of the epidermal layer during skeletonizing or removal of entire portions of leaves by
large larvae.
Birch Leafminer
Description of injury: Birch leafminer larvae mine within the leaves of the host, excavating blotchy mines
(Figure 157). Feeding by several larvae within the same leaf may consume the entire leaf between the
epidermal layers. Leaves turn from silvery to grayish to reddish brown, giving heavily infested trees a
scorched appearance by midto late summer (Figure 158). The several generations per year can cause
heavy, unsightly damage by the end of summer.
Figure 157. Birch leafminer injury, showing characteristic mining between the upper and lower
epidermis of the leaf. Opened mine reveals larva surrounded by fecal pellets.
Figure 158. Overall scorched appearance of a birch tree heavily infested with the birch leafminer.
Hosts: Birch leafminer attacks all species of birches but prefers gray birch, European white birch, and
paper birch; sweet birch is seldom attacked.
Range and site description: This insect is found throughout northeastern North America, from Maryland
northward and westward to Minnesota and Iowa; it also occurs in eastern Canada. It is common on
ornamentals as well as on forest trees.
Insect: Larvae of the birch leafminer, Fenusa pusilla, are yellowish white, flattened, and legless and may
be found in an active mine.
Diagnostics: Since birch leafminers attack new foliage, the periphery of the crown continues to fall
victim to later generations as trees produce new leaves throughout the season. Close examination of the
leaves reveals paper-thin tissue containing dark fecal pellets between the epidermal layers (Figure 157).
New leaves may bear grayish spots where female adults have injured tissues, probing with their
ovipositors during egg-laying (Figure 159).
Figure 159. Leaf injury from ovipositor probing by the birch leafminer.
Locust Leafminer
Description of injury: Adult beetles of the locust leafminer feed on the lower surfaces of leaves in the
spring, skeletonizing them and occasionally eating holes through the leaves (Figure 160). Larvae, which
hatch from eggs laid on the leaves, enter and feed as miners between the epidermal layers of the leaves
(Figure 161). A single larva frequently uses more than one leaf to complete development. By
midsummer, leaves are discolored and have turned red-brown, giving the tree a scorched appearance
(Figure 162).
Figure 160. Locust leafminer injury on locust; adult beetles are also present on the leaf.
Figure 161. Mine caused by larval stage of the locust leafminer.
Figure 162. Discolored, reddish brown appearance of black locust trees heavily damaged by the locust
leafminer.
Hosts: This insect prefers black locust but also attacks birch, beech, apple, cherry, elm, hawthorn, and
oaks.
Range and site description: The locust leafminer is found throughout most of the eastern United States
and Canada wherever its hosts occur.
Insect: Adult Odontota dorsalis beetles are about 1/4 inch (6 mm) long, elongate, flattened, and
orangebrown, with a black stripe on the inner edge of each wing. Larvae are flattened, yellowish white,
and have a darkened head and legs (Figure 163).
Figure 163. Left to right, the larva, pupa, and adult locust leafminer.
Diagnostics: Close inspection reveals leaf tissue removed from the lower epidermis by adult feeding, as
well as shrivelled or papery leaves hollowed out by larval mining. Mined leaves are dry, brittle, and
contain evidence of insect feeding in the form of frass.
Sucking Insects
Periodical Cicada
Description of injury: In midsummer, the female adult periodical cicada cuts jagged slits through the
bark and the wood of succulent twigs, into which she deposits her eggs (Figure 164). With multiple
oviposition slits in a single twig, leaves wilt, die, and turn brown distal to these injured sites. Flagged tips
may break and hang or fall from the tree (Figure 165). In heavy infestations, the periphery of the tree's
crown may appear scorched. In the second year, considerable twig dieback afflicts heavily attacked trees
among the most commonly attacked.
Figure 164. jagged slits cut into a twig by the ovipositor of the female periodical cicada.
Figure 165. Flagging, or brown branch tips, following oviposition by the female periodical cicada.
Range and site description: This insect is widely distributed throughout the eastern United States.
Insect: As an adult, the periodical cicada, Magicicada septendecim, is about 11/2 inches (4 cm) long,
stout- bodied, dark-colored, and has clear, stiff, membranous wings held rooflike over the body at rest
(Figure 166). Nymphs settle on roots about 18 to 24 inches (0.5 m) below the ground surface.
Figure 166. An adult periodical cicada, showing clear, stiff, membranous wings while insect is at rest.
Diagnostics: Leaves are not damaged directly but merely dry up and turn brown from midsummer
onward in years of brood emergence and oviposition. Examination of shoots reveals numbers of ragged
slits about 1/2 inch (12 mm) long through the bark. Slits are often placed end to end, appearing much
longer than they actually are.
Pear Thrips
Description of injury: In the spring of the year, feeding injury of pear thrips is often confused with late
frost damage. Leaves look flaccid and darkened. By August, affected trees turn color prematurely and
drop their leaves. Dieback symptoms have been reported in areas known to have thrips infestations.
This insect has been recognized only recently as being the agent of the reported damage.
Hosts: Red maple, sugar maple, and beech serve as hosts in forested environments.
Range and site description: Although the range of the insect is known to be much larger, in recent years
this insect has been recorded as a pest only in northern Pennsylvania, southern New York, Vermont, and
New Hampshire. One report claims that trees on the highest ground are the most severely attacked, but
this claim has yet to be verified.
Insect: The pear thrips, Taeniothrips inconsequens, is very small, being only about 1/8 inch (3 mm) long
and very slender. Immature stages are wingless. Adults are brown and have two pairs of very long,
narrow wings that are veinless but have a hairy fringe. This insect is not readily seen except through
close observation (Figure 167).
Figure 167. Adult pear thrips on maple bud scales, showing the comparative small size of this insect.
Diagnostics: Pear thrips have rasping and sucking mouthparts and feed on the surface of leaves. Infested
leaves look tattered (Figure 168).
Figure 168. Tattered sugar maple leaf caused by pear thrips feeding.
Meristernatic Insects
Bronze Birch Borer
Description of injury: Bronze birch borers normally attack the crown first, causing individual shoot or
branch mortality, chlorosis of foliage, and an overall appearance of decline (Figure 169). Eggs are laid in
crevices and cracks, often near branch axils. Larvae mine directly into the cambium and often girdle the
branch or bole of the tree with meandering tunnels between the bark and the wood (Figure 170).
Tunnels of older larvae may occasionally penetrate the wood and are normally packed with powdery
frass. Portions of branches or stems distal to the area of girdling usually decline and die; stems
frequently break off at areas of attack (Figure 171). Trees or branches more than about 1 inch (2 to 3
cm.) in diameter are subject to attack.
Figure 169. Declining birch trees following infestation of branches and main stems by the bronze birch
borer.
Figure 170. Mines and swollen bark areas caused by larvae of the bronze birch borer on white birch.
Figure 171. Stem breakage in a white birch stand. Most breaks occur at the point of girdling by bronze
birch borer larvae.
Hosts: European white birch, paper birch, and yellow birch are the preferred hosts.
Range and site description: Bronze birch borer, found throughout the range of birches in the United
States and Canada, tends to attack weakened trees or trees on poor sites.
Insect: Adults of the bronze birch borer, Agrilus anxius, are bronze-green and about 1/4 to 1/2 inch (6 to
12 mm) long. Full-grown larvae are about 1 inch (2 to 3 cm) long and are typical of flat-headed wood
borers. They are creamy white, compressed dorsoventrally, have an enlarged, wide thoracic area, and
have two spines at the posterior end of the abdomen.
Diagnostics: Any above ground portion of the tree may be attacked. Raised welts over the larval tunnels
may be observed on the bark of trees under attack (Figure 170). Breakage of trees, especially in the
winter, commonly occurs at weakened places in the bole. D-shaped exit holes may be seen after beetle
emergence, between late May and August. The head and thoracic segments of overwintering larvae are
characteristically doubled back over the anterior part of the abdomen (Figure 172).
Figure 172. Overwintering bronze birch borer larva, showing characteristic shape of doubling back of
head and thorax over the anterior portion of the abdomen.
Conifer Insects
In the Southeast, bark beetles are the most important insect pests of conifers. Along with some of the
other meristematic insects, they are most likely to cause symptoms that might be confused with air
pollution damage. Defoliators and sucking insects such as the gall adelgids are more important in the
northeastern and New England states.
Leaf-eating Insects (Defoliators)
Eastern Spruce Budworm
Description of injury: After overwintering in a silken hibernaculum as a second instar larva (Figure 173),
the eastern spruce budworm moves to the exterior of the crown early in spring, seeking staminate
flowers. Lacking these, larvae mine one to several old needles while awaiting budbreak, at which time
they attack new foliage. As the season progresses, larvae consume older foliage as well, foraging out
from loosely constructed silken shelters, which they make by tying together needles from adjacent
twigs. By early to midsummer, the injured and dying, but not fully consumed, needles give tree crowns a
reddish brown, burned appearance. After repeated defoliation, crowns are fully open, thin, and sparsely
foliated. Thousands of hectares have been killed annually in eastern North America.
Figure 173. Silken hibernaculum of a second instar larva of the eastern spruce budworm on balsam fir.
Hosts: Hosts include balsam fir, white spruce, and red spruce. In the various parts of its range, this insect
feeds on at least twenty-five species of conifers, including eight of spruce, six of pine, five of fir, three of
hemlock, two of larch, and juniper
Range and site description: Eastern spruce budworm is the major defoliator of balsam fir and spruce in
the northeastern United States, in the Great Lakes region, and across eastern Canada.
Insect: The larva of eastern spruce budworm, Choristoneura fumiferana, is fully grown by June or July. It
is about 1 inch (2 to 3 cm) long, has a dark head capsule, and is brownish green dorsally and spotted
with white laterally (Figure 174).
Figure 174. Larva of the eastern spruce budworm, showing dark head capsule, white spots, and
brownish green color.
Diagnostics: Observe closely to detect early feeding and mining on buds and in needles. Larvae spin
down from the foliage on silken threads when limbs are jarred. This insect prefers new foliage, so the
tops of trees and the crown periphery are most noticeably defoliated (Figures 175, 176).
Figure 175. Injury to crown periphery of red spruce; caused by the feeding of the eastern spruce
budworm.
Figure 176. Defoliation of red spruce branch terminals; caused by the eastern spruce budworm.
Nantucket Pine Tip Moth
Description of injury: Nantucket pine tip moth larvae mine the growing shoots of pine trees. As the
shoots die, the tips of the trees turn brown (Figure 177, 178). All new growth may be killed where
population levels are high; however, where populations are low, only the buds and the most distal
portions of the shoots may be killed. In areas where tip moth populations are high, these insects attack
virtually every tree in the stand.
Figure 177. Terminal bud and shoot death of pine; caused by larval mining by the Nantucket pine tip
moth.
Figure 178. Damaged shortened new shoots on Scots pine as a result of attack by Nantucket pine tip
moth.
Hosts: Preferred hosts include all southern pines, especially shortleaf pine; longleaf pine is less often
attacked, and slash pine is attacked infrequently.
Range and site description: Nantucket pine tip moth is widely distributed in the eastern United States
and is of particular importance to pines in the southeastern United States from Maryland to Texas.
Populations are especially heavy on stressed sites in the Coastal Plain and on poor sites in the Piedmont
areas. In all susceptible areas, heavy moth populations can be expected on intensively managed,
mechanically prepared sites and where herbaceous weed control is practiced.
Insect: Adults of the Nantucket pine tip moth, Rhyacionia frustrana, are inconspicuous, brownish gray
moths with wing spans of less than 3/4 inch (18 mm). Larvae are light brown to orange and grow to a
maximum length of about 1/3 inch (8 mm).
Diagnostics: Early attacks are characterized by silvery webs between buds which are coated with fresh
resin. Old attacks can be identified by the dead, brownish shoots that easily crumble when pressed
between the thumb and fingers. These dead shoots may have yellow, crystallized resin beads on the
buds.
Hemlock Loopers
Description of injury: Hemlock looper larvae damage trees by feeding on foliage. Heavy defoliation kills
individual trees or groups of trees; more moderate defoliation slows tree growth. The larva's habit of
consuming only a part of the foliage increases damage. Young larvae eat the edges of needles but leave
a central filament which eventually dries out, curls, and turns reddish brown. Older larvae commonly
move from needle to needle, taking only a few bites from near the base. These needles then die,
showing the same scorched symptoms described earlier. Other needles are severed at or near their base
and simply drop to the ground. In a heavy defoliation, enough needles are killed and removed that twigs
are exposed directly to sunlight and may die.
Partial defoliation reduces annual growth, and successive years of partial defoliation often weaken the
tree enough to allow other pests to become established and ultimately contribute to tree mortality.
Hosts: Hemlock loopers are common in eastern hemlock, balsam fir, and spruce forests. Several species
and subspecies of hemlock loopers attack hemlock and other conifers in eastern North America.
Lambdina athasaria occasionally appears on eastern hemlock. During most years, however, the insect
seems to go unnoticed and frequently unreported. Lambdina fiscellaria, a more widespread species,
commonly feeds on balsam fir as well as hemlock. When populations are very heavy, it may move to
other native conifers as well as hardwoods, including birch, maple, and aspen. Outbreaks tend to occur
in overmature stands of host trees.
Range and site description: Hemlock loopers are found throughout the northeastern United States and
across Canada from Newfoundland, at least as far west as the Rocky Mountains.
Insect: Hemlock loopers, Lambdina spp., overwinter in the egg stage. Eggs are frequently laid on twigs
near the bases of needles and occasionally on the trunks of trees. They are also laid singly or in small
groups under lichens, in bark crevices, in moss growing on old stumps, and on trunks and branches of
host trees. Eggs are not covered by any frothy or setaceous protective material. Young larvae initially
feed on the succulent new needles. Larvae are greenish gray to brown, with lateral, paler stripes. They
move in the typical inchworm fashion, looping along on the needles or branches (Figure 179).
Figure 179. Side view of looping or inchworm nature of hemlock looper larva.
Diagnostics: From a distance, the crown of a tree attacked by hemlock loopers appears thin and
unthrifty (Figure 180). Closer examination may reveal a number of severed needles that have fallen to
the ground under the canopy and portions of needles, usually discolored and shrivelled, still on the tree.
Where pieces of needle have been removed, the physical damage is quite obvious.
Figure 180. Thin appearance and mortality of crowns of eastern hemlock defoliated by hemlock looper.
Introduced Pine Sawfly
Description of injury: Larvae of the introduced pine sawfly damage host trees by attacking mature
foliage. First- generation larvae consume entire needles of the previous years' growth, thinning the
crown, especially in the upper half. The second generation feeds on the remainder of the old foliage and
on the hardened-off foliage of the current year. Larvae also may feed on the bark of completely
defoliated trees. Sawfly defoliation (Figure 181) commonly retards radial and terminal growth and
occasionally kills branches and trees (Figure 182). At high population levels, the sawfly can cause
complete defoliation, and, if the buds are also destroyed, can kill the trees as well.
Figure 181. Crown defoliation of eastern white pine; caused by feeding activity of the introduced pine
sawfly.
Figure 182. Browning of individual needles and shoot dieback; caused by feeding of the introduced pine
sawfly.
The early instars feed gregariously, moving from the needle tip to the base and leaving only the central
vascular tissue (Figure 183). By the end of the third instar, larvae feed solitarily and consume the entire
needle.
Figure 183. Young larvae of introduced pine sawfly feeding gregariously on a single needle.
Cocoons are constructed on any solid object above ground, commonly in clusters, and in protected
areas (Figure 184). Larvae of the overwintering population may spin cocoons in the duff. The cocoon is a
tough, cylindrical, silken capsule that is white when newly spun but turns brown with age.
Figure 184. Cocoons of the introduced pine sawfly on a totally defoliated eastern white pine.
Hosts: The introduced pine sawfly feeds on a wide range of pines, including white, red, Scots, jack, and
Austrian. Although other species have been shown to be suitable for oviposition and survival of eggs and
larvae, white pine is the preferred and most suitable host. The sawfly rarely causes significant
defoliation on other pine species. Defoliation is normally not a problem on seedlings, but all other age
classes are susceptible.
Range and site description: This insect, introduced from Europe, occurs in natural stands, plantations,
and Christmas tree plantations. It is found from Maine to Virginia and west to the Great Lakes states, as
well as in southeastern Canada.
Insect: The adult female of the introduced pine sawfly, Diprion similis, lays small, oval eggs serially in
slits that she cuts in the needle. These cuts may create some confusion with symptoms of the needlecast
fungi. The eggs are pale blue when first deposited and turn turquoise as they mature.
When first-instar larvae hatch following oviposition in the spring, they are about 1/4 inch (6 mm) long
and have white head capsules and dull gray bodies. Shortly after emergence, the head capsule turns
shiny black, the legs black, and the body a yellowish green. By the third instar, the larvae are slightly
darker. By the fourth instar, coloration changes markedly; two black middorsal lines and numerous
lateral yellow and white spots appear. The fifth and sixth instars have a distinct mottled pattern and
reach a length of about 1 inch (2.5 cm). These instars have a light green to gray head capsule (2 to 3 mm)
and very light and dull body markings. When disturbed, late instar larvae characteristically react by
arching their heads over their backs and regurgitating a dark, oily fluid.
Diagnostics: Partial defoliation, starting from the top down, appears as a symptom of crown decline and
may be confused with crown decline caused by other organisms. For a proper diagnosis, presence of the
easily observed larval or cocoon stages should be confirmed.
Sucking Insects
Balsam Woolly Adelgid
Description of injury: The balsam woolly adelgid, formerly known as the balsam woolly aphid, is native
to the silver fir forests of central Europe. The insect was introduced into North America about 1900. A
continuous, heavy infestation frequently causes crown dieback, and, within two to six years, tree
mortality occurs (Figure 185). Infestations can occur on the tree trunk, in the crown, or both (Figures
186, 187). Stem attack appears to be lethal to the host.
Figure 185. A large stand of Fraser fir killed by the balsam woolly adelgid.
Figure 186. Balsam woolly adelgid infestation on the trunk of Fraser fir.
Figure 187. Twig gout caused by the balsam woolly adelgid on Fraser fir.
Once it finds a suitable feeding site, the insect inserts its stylet into the bark; it is then restricted to that
location for the remainder of its life. As the insect feeds, it secretes saliva through the stylet, thereby
stimulating an increase in the size and number of parenchyma cells in the feeding zone. The infestations
cause gout, a syndrome characterized by enlarged nodes and buds (Figure 187). Gout reduces growth of
new foliage by inhibiting the conduction of water and nutrients. Top kill from gout is common; affected
trees assume a flattopped appearance.
Hosts: Fraser fir and balsam fir are particularly susceptible to attack. All size classes are infested. In
natural stands, however, mature trees usually support the largest populations, probably because they
intercept more winddispersed crawlers. Seedlings under a heavily infested overstory occasionally
become infested. Fraser fir infestations consist mainly of stem attacks; in bracted balsam fir, crown
infestations are more common.
Range and site description: Infestation patterns vary with region and host. Crown infestations
predominate in the coastal areas of the balsam fir range, while stem attacks are more common inland.
The adelgid, discovered in the southern Appalachians in 1956, infests Fraser fir in North Carolina and
bracted balsam fir in Virginia. It is found on balsam fir from New England to as far south as New York and
in eastern Canadian forests.
Insect: The balsam woolly adelgid, Adelges piceae, overwinters as a dormant first-instar nymph. In
spring, the nymphs begin to secrete waxy strands of wool, which eventually cover the entire body. At
maturity - by late May - eggs are oviposited within the wool mass; most firstgeneration eggs hatch by
the end of June. At low elevations, additional generations are possible.
Diagnostics: The best diagnostic tools are obvious signs of the insect on the bark of infested stems and
the presence of the gout symptom. The flattop and red crown of individual trees in advanced stages of
decline are easily seen on sites where the insect has existed over a period of years.
Balsam Twig Aphid
Description of injury: The unique injury caused by the balsam twig aphid cannot be easily confused with
injury caused by anything else. New needles appear curled and twisted, and large numbers of aphids
feed within the curled foliage (Figure 188). Most of the twisted needles of mature trees will remain
distorted. When populations are extremely high, the aphids are frequently observed migrating up and
down the tree (Figure 189). Cast skins and black eggs covered with tiny rods of white wax occur on the
needles, twigs, and main stem (Figure 190). These signs can be confused with the damage symptoms of
the balsam woolly adelgid.
Figure 188. Curled and twisted foliage of balsam fir; caused by feeding of the balsam twig aphid.
Figure 189. Balsam twig aphid on new foliage; cast skins are also evident.
Figure 190. Black eggs of balsam twig aphid covered with rods of white wax.
Hosts: All fir species of all ages are attacked. Species and varieties that break bud earliest seem most
susceptible to injury. The balsam twig aphid has also been reported on white spruce.
Range and site description: Found throughout eastern North America, the balsam twig aphid may injure
any sections of the crown, regardless of level or aspect.
Insect: The balsam twig aphid, Mindarus abietinus, excretes large quantities of waxy, white wool as well
as sticky honeydew. A winged generation allows the aphids to fly to adjacent trees. In the summer
months, winged insects are naked, pale green, and are located in clusters on the needles and shoots.
Diagnostics: Twisted and curled new needles and the presence of the aphid are the best diagnostic
tools. In addition, the presence of honeydew and the associated sooty mold fungi on the foliage are
indicative of attack.
Description of injury: Aphids usually live in colonies up to 3 to 4 inches (7 to 10 cm) long, clustered
around a branch or leader. Young trees or individual branches of older trees may be killed. Heavy
infestations of aphids can significantly reduce tree growth. Aphids also produce prodigious amounts of
honeydew, an excretion that contains sugars; this excretion is frequently colonized by black sooty mold
fungi (Figure 191). Sooty mold does not directly injure the tree, but it can interfere with photosynthesis.
Infestations in forest stands can consist of individual trees, or, if aphid populations are high, many trees
throughout the stand may be affected.
Figure 191. Black colonies of the sooty mold fungus growing on aphid or scale exudate on the surface of
Scots pine needles.
Hosts: All southern and eastern pines and most hardwoods are susceptible.
Range and site description: Infestations are found anywhere hosts grow. Low-vigor trees on poor sites
are especially susceptible to aphid attack.
Insect: Aphids associated with sooty mold, commonly Cinara spp., are soft-bodied insects ranging in size
from 1/25 to 1/4 inch (1 to 6 mm) long. Most aphids are pear-shaped and have a pair of cornicles
(projections) on the posterior dorsum of the abdomen. Most pine aphids are brown to black.
Diagnostics: Dieback or flagging of branches and terminals are symptoms on heavily infested trees.
Sooty mold and ants frequenting a tree are also good indicators of aphid attack. In addition to its
association with aphids, sooty mold is also associated with scale insect infestations.
Pine Leaf Adelgid
Description of injury: The pine leaf adelgid attacks spruce and pine and has a complex life cycle that
comprises five distinct forms or stages. Injury associated with these stages includes gall formation at the
base of spruce buds and feeding at the base of spruce needles. Damage on spruce is not serious, as
there are usually sufficient numbers of uninfested buds. On white pine, however, the insect causes
shoots to droop and eventually die; needles on affected shoot tips turn red (Figure 192). On white pine,
the adelgid produces a waxy covering on the axils of new shoots and then lives in these axils. The insect
occasionally kills whole trees.
Figure 192. Mortality of eastern white pine shoots; caused by feeding activity of the pine leaf adelgid.
Hosts: Red and black spruce, white pine, and occasionally red, Scots, and Austrian pine are hosts of the
pine leaf adelgid.
Range and site description: This insect is found in Maine, New Hampshire, Vermont, New York, and
throughout Canada. Site specificity is not known.
Insect: The pine leaf adelgid, Pineus pinifoliae, has five different morphological forms and attacks both
spruces and pines. Some adelgids are cryptic, living within galls; others bear a waxy, flocculent covering
that is more easily seen than the small nymphs themselves.
Diagnostics: Presence of the dormant first-stage larvae at the base of pine needles is the most distinctive
signal for diagnosing an outbreak. Insects are present on new shoots of pine from July until the following
May. On spruce, a compact gall resembling a cone may be found on the tip of the new growth.
Dead adults, often lined up in rows, may be found for several months on the needles. On pine, they are
invariably oriented with the head toward the base of the needle; on spruce, with the head toward the
tip of the needle.
Pine Bark Adelgid
Description of injury: Needles distal to infested portions of branches may turn yellow (Figure 193), die,
and fall (Figure 194). Small trees may become stunted, or, rarely, die if heavily infested. Larger trees may
appear off- color if under heavy attack, but they seldom suffer any permanent damage if otherwise
healthy.
Figure 193. Yellowing of eastern white pine as a result of infestation by the pine bark adelgid.
Figure 194. Pine bark adelgid infestation on Scots pine shoot. Some needles are turning brown as a
result of twig attack.
Hosts: White, Scots, Austrian pine, and occasionally spruce serve as hosts.
Range and site description: The species is widely distributed throughout North America, occurring
wherever white pines grow.
Insect: The pine bark adelgid, Pineus strobi, is small, dark, and covered with white flocculent wax. When
numbers of insects occur together, they give the appearance of white, cottony spots or patches on the
trunks, or, most commonly, on the undersides of limbs of host trees (Figure 195). They may also occur
on twigs at the bases of needles or buds (Figure 196). Extremely heavy infestations may give the trunk of
a tree the appearance of having been whitewashed. Eggs are laid in the spring by the mature females
that have overwintered; although some winged individuals are produced, most are of the wingless form.
This form remains on the pine host and produces up to five generations during the year; winged
individuals may fly to other hosts, including spruce, to deposit eggs.
Figure 195. Pine bark adelgid infestation on branches of Scots pine.
Figure 196. Pine bark adelgid nymphs feeding on candles of Scots pine early in the season.
Diagnostics: Small to large white spots or patches, or, in extreme cases, a whitewashed appearance of
the trunk, suggest the presence of this insect (Figure 195). On close examination, small, dark insects with
sucking mouthparts inserted into the substrate are revealed under the cottonlike waxy covering.
Occasionally, yellowish or thinned foliage, especially on younger trees, may indicate the presence of this
insect.
White Pine Aphid
Description of injury: Tree mortality, stunting, or branch killing may occur as a result of colonies of large
numbers of white pine aphids feeding on young trees or on branches of older trees. Large quantities of
honeydew, excreted by the aphids as they feed, provide a substrate for the growth of a black, sooty
mold that is unsightly, interferes with normal tree growth, and reduces tree quality.
Hosts: Eastern white pine.
Range and site description: The insect occurs from New England to the Lake states and the Carolinas.
Insect: The white pine aphid, Cinara strobi, is a shiny, dark brown insect about 1/8 inch (4 mm) long in its
winged form, with a white stripe down the middle of the dorsum, powdery white spots on its sides, and
long, stiff hairs on the body. Eggs are laid in a row on needles of the host in the fall and overwinter. In
the spring, these eggs hatch to produce wingless females, which reproduce parthenogenetically through
several generations in spring and summer. Feeding occurs colonially in clusters up to about 20 to 25
inches (75 to 100 mm) long around branches or leaders of the trees (Figure 197). In the fall, both male
and female winged forms are produced, mating takes place, eggs are deposited, and the annual cycle is
completed.
Figure 197. White pine aphid feeding colonially on shoot of eastern white pine.
Diagnostics: Colonies of aphids encircling branches or the leader, the presence of unsightly black, sooty
mold, and needle discoloration or branch flagging distal to the point of feeding are all evidence of attack
by this insect. Ants frequently attend the aphids, feeding on the honeydew produced.
Cooley Spruce Gall Adelgid
Description of injury: On spruces, the Cooley spruce gall adelgid causes swelling of the stem at the bases
of needles on new shoots, giving rise to green or purplish galls (Figure 198). By late fall, the foliage and
gall tissue turn reddish brown (Figure 199), and cavities appear where the tissues separate to allow the
insects to emerge. Galls persist on trees for a year or more.
Figure 198. Green (spring) galls on Colorado blue spruce; caused by the Cooley spruce gall adelgid.
Figure 199. Brown (fall) galls on Colorado blue spruce; caused by the Cooley spruce gall adelgid.
On Douglas-fir, this insect causes twisted needles with chlorotic spots but no galls.
Douglas-fir trees infested with large populations take on a yellowish green cast and appear unthrifty and
chlorotic. A fairly distinct bend, caused by insertion of the sucking mouthparts of the nymphs, exists at
some point along each twisted needle.
Hosts: In the East, white, Norway, and several ornamental spruces are important hosts; Douglas-fir is
less important.
Range and site description: This insect occurs coast to coast in the northern United States and
throughout the range of white spruce in Canada.
Insect: The Cooley spruce gall adelgid, Adelges cooleyi, has six different morphological forms, depending
on time of year and host. The young crawlers, which are very tiny, may be seen in early spring, clustering
around the buds on spruce at about the time the bud cap cracks. During most of the rest of their
development on spruce, the insects are cryptic.
Diagnostics: This insect is easily identified on spruces by unsightly reddish brown galls and killed shoots
while needles are still present. On Douglas-fir, individual twisted needles are not especially noticeable,
except in heavily infested trees.
Spruce Spider Mite
Description of injury: Mites, although not insects, are closely related arthropods; some species cause
injuries similar to those caused by insects. The spruce spider mite is probably the most destructive
conifer-feeding mite; it feeds by inserting its stylet-like mouthparts into a needle and extracting the
contents of the cells, causing needle chlorosis. Under less severe feeding, foliage appears mottled or
bleached (Figure 200). Resultant damage may be restricted to a slight reduction in radial and
longitudinal growth for the year. In severe infestations, needles may become enwebbed in the fine silk
spun by the mites as they move about (Figure 201). Affected needles may become entirely bronzed and
drop off prematurely, tree growth may be greatly retarded, and, occasionally, trees may die. Spruce
spider mite populations build up most rapidly during hot, dry seasons.
Figure 200. Bleached appearance of spruce foliage heavily infested with spruce spider mites.
Figure 201. Silken web of the spruce spider mite containing frass and needle debris and surrounding
new buds.
Hosts: The spruce spider mite has a wide range of coniferous hosts in the United States, including many
species of spruce, fir, and pine. Other genera that have been attacked by the mite include juniper,
cypress, cedar, Port-Orford-cedar, incense-cedar, and sequoia.
Range and site description: The spruce spider mite is found throughout North America. Major
infestations may occur on ornamentals and in nurseries, plantations, or natural stands.
Insect: The spruce spider mite, Oligonychus ununguis, deposits pale green eggs that turn amber shortly
after deposition. They are small, globular, somewhat flattened, and have a distinct central seta. Nymphs
and adults have four pairs of legs. Adults vary from dark green to black and have a pale streak extending
along the middorsal line (Figure 202).
Figure 202. Spruce spider mite adult and egg at base of needle. Note small size in comparison to needle
width.
Diagnostics: Individual spider mites are difficult to observe with the naked eye. A reliable means of
detection is to sharply jar a branch over a piece of white paper and watch for tiny crawling objects. A
hand lens is useful.
The presence of mites can usually be detected by looking for the fine, dust-coated webbing of the insect
and for shed needles and similar debris.
Since injury symptoms range from flecking, stippling, or bleaching to total foliage bronzing, needle drop,
and tree death, the spider mite injury or damage could be mistaken for something else, especially
pollution injury. Suspected foliage should always be examined for one of the spruce spider mite's life
stages and for silken webbing. Clear to slightly opaque egg cases are detectable with the aid of a hand
lens.
Thrips: Short-Needle Of Scots Pine
Description of injury: Shortneedle injury as caused by thrips is characterized by a stunting of one or both
needles in some fascicles; needles in other fascicles on the same shoot elongate normally (Figure 203).
This stunting appears to be caused by the probing of insects into the meristematic area at the base of
the needle just before or during needle elongation (Figure 204). Injured needles fail to elongate fully.
Heavy infestations render the trees ragged-looking.
Figure 203. Short-needle of Scots pine; caused by thrips feeding at needle bases.
Figure 204. Feeding injury at needle base of Scots pine; caused by thrips.
Hosts: Hosts include Scots and Austrian pine and, occasionally, eastern white pine.
Range and site description: Thrips-induced short-needle has been found throughout the midAtlantic
states and perhaps elsewhere.
Insect: Thrips are in the order Thysanoptera. Adult thrips are black, have two pairs of long, narrow wings
fringed with hairs, and are usually less than 1/4 inch (6 mm) long. The tiny nymphs are active, slender
insects that usually hide themselves in protected places, such as between needles in the fascicle.
Nymphs resemble adults in shape but lack wings and are orange-yellow.
Diagnostics: Look for needles of different length in the same needle fascicle. With a hand lens, look for
injury at the base of needles.
Pine Spittlebug
Description of injury: This insect is a sapfeeder on young shoots and twigs. Heavy infestations may lead
to main stem feeding on young trees. Initial injury is difficult to detect and consists only of slight
discoloration of fed-upon bark tissues and necrotic spots in the underlying wood. The presence of
spittle, evident as frothy masses at bases of needles (Figure 205) or along stems (Figure 206), is the best
evidence of insect attack. Prolonged feeding activity will cause shoots and needles to turn red and die.
Young trees, especially those in plantations, or trees in stagnating stands may be weakened; they may
die in one to three years if attack continues.
Figure 205. Spittle mass caused by pine spittlebug feeding at the base of needles on Scots pine.
Figure 206. Spittle mass surrounding twig of Scots pine as a result of feeding by the pine spittlebug.
Hosts: Scots pine is most susceptible, but eastern white pine and jack pine also serve as hosts. The insect
may be found on numerous other pines, balsam fir, hemlock, and spruce species.
Range and site description: The spittlebug may be found throughout the range of its hosts in the eastern
United States. The insect does not appear to be site specific but has been found to be damaging in polesized Scots pine plantings and Christmas tree plantations.
Insect: The pine spittlebug is Aphrophora parallela. Eggs are laid in dead woody tissue or under the bark
of shoots in summer and serve as the overwintering stage. Nymphs emerge in the spring and are black
in front and orange to the rear. They are enveloped in spittle as they feed. Adults are gray to brownish
black, boatshaped, and about 1/3 to 1/2 inch (8 to 11 mm) in length. They respond to touch by jumping.
Diagnostics: The presence of spittle as a frothy mass, the insect itself, and reddened twigs and branches
are all evidence of insect attack. Most nymphal feeding takes place on growth of the previous year.
Meristernatic Insects
White Pine Weevil
Description of injury: Adults of the white pine weevil feed on succulent terminal portions of branches in
the fall and on elongating terminals and leaders in the spring, often causing small flows of resin (Figure
207). Eggs are laid in the spring of the year in feeding cavities excavated in leaders. Larvae hatch, form a
feeding ring encircling the leader under the bark, and mine their way downward. This feeding activity
destroys the cambium and commonly kills the last two to four years of leader growth (Figures 208, 209).
Dead leaders break out from the trees. In late summer, larvae excavate chambers in the woody tissue or
in the pith, where they pupate and from which they emerge as adults in the fall of the year. The insect
not only destroys the leader but also causes forked tops because the damage extends back into stem
tissue that is several years old.
Figure 207. Resin exudation and feeding punctures caused by an adult white pine weevil feeding on an
eastern white pine terminal.
Figure 208. Mortality of terminal shoot of eastern white pine; caused by the white pine weevil.
Figure 209. Mortality of leader of spruce; caused by white pine weevil.
Hosts: In the eastern United States, white pine weevil may attack eastern white pine, jack pine, Scots
pine, red pine, red spruce, black spruce, and Norway spruce,
Range and site description: This insect is found over much of eastern North America, throughout the
range of eastern white pine. Trees ranging from 4 to 25 feet (1 to 8 in) are particularly susceptible to
attack. Attacks may be much higher in older trees.
Insect: Grublike larvae of the white pine weevil, Pissodes strobi, mine in the cambial area in early
summer; larvae or pupae may be found in fibrous cocoons within the leader in late summer. Adult
weevils may be seen occasionally in the fall feeding on small twigs or more easily on elongating candles
in the spring (Figure 207).
Diagnostics: Look for small, glistening beads of resin on leaders in early spring or on laterals in fall; these
beads are caused by adult feeding. In early to midsummer, the needles on currently infested leaders wilt
and then turn red or brown; leaders may exhibit drooping crooks (Figures 208, 209). Dead leaders and
forked tops, or boles with crooks, signify prior attacks. After adults emerge in early fall, round exit holes
are visible in the killed portion of the leader.
Other Pissodes Weevils
Description of injury: Weevils feed on the inner bark of twigs, branches, and main stems of small trees.
Especially in the South, infested branches start fading in late winter, and, by spring, foliage on damaged
branches is red. The needles have a scorched appearance, particularly in the topmost branches on the
tree. Small trees may be killed.
Hosts: Most pines, including Scots, white, Austrian, and southern, and true cedars are hosts.
Range and site description: These weevils are found throughout the eastern and southern United States.
Insect: Adults of Pissodes spp. are red to grayish brown and about 1/6 to 1/3 inch (4 to 8 mm) long
(Figure 210). The larvae are legless and appear as white grubs that feed in the phloem and xylem.
Figure 210. Northern pine weevil adult on stem of Scots pine.
Diagnostics: On recently attacked trees, feeding scars are evident on the bark of twigs and small
branches. These feeding wounds, in combination with fading foliage, are characteristic of weeviled trees
(Figure 211). Females lay eggs in the holes made while feeding. The larvae feed in the inner bark - which
often swells over the feeding sites - and pupate in chip cocoons, which are shallow depressions or
chambers in the sapwood with a layer of long, yellowish white wood fibers on top. Some Pissodes
species attack stumps or logs. Chip cocoons in dead twigs are good indicators of the presence of these
weevils (Figure 212).
Figure 211. Feeding wounds and scars on pine; caused by Pissodes weevils.
Figure 212. Chip cocoon formed by mature Pissodes approximatus weevil larva.
Engraver Beetles
Description of injury: The most visible symptom of injury is yellow-green to reddish brown foliage
(Figure 213). Over a period of weeks, foliage on pine trees fades from green to red, and the dead
needles eventually fall from the trees. Secondary signs of injury include the presence of creamy white to
reddish brown pitch tubes on the bark and reddish brown boring dust in bark crevices. Occasionally,
only the upper portion of the crown of the tree is killed, leaving branches with green foliage at the base
of the crown. Within stands, trees are usually killed in groups, although single tree kills are not
uncommon.
Figure 213. Brown foliage of pine attacked by Ips engraver beetles.
Hosts: Most pines, including all southern pines, may be attacked.
Range and site description: These insects may be found wherever southern pines grow. Outbreaks of
engraver beetles are often associated with prolonged periods of drought. Stand disturbance, such as
lightning, fire, or logging damage, can trigger outbreaks of this pest.
Insect: Adult engraver beetles, Ips spp., are dark red to brown and about 1/5 inch (5 mm) long. The
posterior of the adult beetle has a scooped-out appearance; up to six spines are on each side of the
declivity. The creamy white, legless larvae are found in the inner bark of the tree. Pupation also takes
place in the bark.
Diagnostics: The presence of these engraver beetles is indicated by fading foliage in combination with
pitch tubes or boring dust. Ips engraver beetles can usually be distinguished from other bark beetles by
the presence of Yor H-shaped egg galleries that parallel the wood grain (Figure 214), in contrast to the
meandering egg galleries excavated by other treekilling bark beetles. Fading of the tree crown is a
common symptom caused by all species of bark and engraver beetles.
Figure 214. Galleries of Ips avulsus beetle larvae and pupal cells in phloern.
Southern Pine Bark Beetle
Description of injury: Because the southern pine bark beetle develops so quickly, new attacks and
infestations occur continuously over periods of months. Attacks often occur in mature and overmature
stands on poor sites; trees under stress are also at risk. Large numbers of beetles attack and overcome
individual trees, causing large numbers of pitch tubes on the boles (Figure 215). Once trees have been
girdled by the construction of meandering, S-shaped oviposition galleries or through the larval feeding
activities (Figure 216), their foliage fades from green through yellow to reddish brown, and they die.
Trees are typically attacked and killed in patches (Figure 217). Beetles move to adjacent trees after
adults emerge.
Figure 215. Crystallized resin "popcorn" on trunk of pine recently attacked by the southern pine beetle.
Figure 216. Typical sinuous galleries of the southern pine beetle in phloem/cambial area of loblolly pine.
Figure 217. Stand of loblolly pine killed by the southern pine beetle.
Hosts: Shortleaf, slash, and loblolly pine are most commonly attacked, but all species of pine within the
range of the insect are susceptible, especially under outbreak conditions. Longleaf pine is seldom
attacked.
Range and site description: Southern pine bark beetle occurs in the eastern United States, from
Delaware south to Florida and west to Texas. Stands with high basal areas, overstocked or slowly
growing stands, and stands on poorly drained lowland sites are most susceptible to attack.
Insect: Adults of the southern pine bark beetle, Dendroctonus frontalis, are brownish black, less than
1/6 inch (4 mm) long, and, unlike the Ips species, have no elytral depression (Figure 218). Larvae are
small, off-white, legless grubs with distinct, darkened head capsules. The adults enter the bole of the
tree to construct sinuous, S-shaped egg galleries in the phloem-cambium area and to lay eggs in niches
along the walls of these galleries. As they feed, larvae mine away from the egg gallery, entering the bark.
Adults emerge through small, round holes in the bark.
Figure 218. Adult southern pine beetle showing convex posterior.
Diagnostics: Pitch tubes, fine, reddish, powdery frass around the base of a tree and in bark crevices, and
small, round emergence holes in the bark are all signs of the southern pine bark beetle. Egg galleries are
characteristically serpentine; staining fungi may be evident in the associated wood. Foliage fades from
green through yellow to reddish brown as the tree dies. Dead trees are normally found in patches,
which may coalesce during major outbreaks.
Spruce Beetle
Description of injury: Spruce beetle first attacks the lower third of the bole above the stump. It may
eventually attack the entire bole, except for the upper part under 8 inches (20 cm) in diameter. Limbs
are not infested. Beetles attack slowly, continuously, and without major swarming. The attack lasts from
a few days to many months, depending on beetle population density, host resistance, and
environmental conditions. Feeding eventually causes the foliage to wilt and turn brown (Figure 219).
Resin flow and pitch tubes can be seen at the adult entrance holes. Portions of attacked trees may die,
while other portions remain green for several months; death may occur one year or more after attack.
Figure 219. Thin, dying crowns of red spruce; caused by the spruce beetle, Dendroctonus rufipennis.
Egg galleries are almost straight, parallel to the grain, and often packed with frass (Figure 220). Near
entrance holes, the galleries are often hooked diagonally to the left or right for a short distance. After
eggs hatch, the larvae feed communally for a while, then burrow lateral, independent galleries that may
cross each other.
Figure 220. Typical straight- and parallel-to-the-grain gallery of spruce beetle under the bark of red
spruce.
Hosts: All species of spruce within range of the insect may serve as hosts.
Range and site description: Spruce beetle is found from Alaska to Newfoundland and south to Arizona,
New Mexico, Michigan, and Pennsylvania. Spruce beetle prefers to attack mature and overmature
stands, along with freshly cut logs and shaded slash. It also invades weakened standing or fallen green
trees, usually only if they are more than 8 inches (20 cm) DBH. During major outbreaks, any tree in the
stand is susceptible to attack.
Insect: Adults of the spruce beetle, Dendroctonus ruflpennis, are about 1/5 inch (5 mm) long and dark
brown; they have reddish brown elytra that darken with age. Larval galleries tend to coalesce early in
development. Larvae are legless, white, slightly C-shaped, and have a distinct, dark head capsule.
Diagnostics: Feeding beetles loosen the bark, and feeding galleries are readily discernable under the
bark. Reddened top foliage and resin masses at the base of the tree are other diagnostic features.
Common and Scientific Names
Forest Species
Alder, Hazel Alnus serrulata (Ait.) Willd.
Apple, Common Malus pumila Mill.
Ash, Green Fraxinus pennsylvanica Marsh.
Ash, White Fraxinus americana L
Aspen, Bigtooth Populus grandidentata Michx.
Aspen, Quaking (Trembling) Populus tremuloides Michx.
Aster Aster Spp.
Basswood Tilia americana L.
Bearberry Uva-ursi uva-ursi (L.) Britton
Beech, American Fagus grandifolia Ehr.
Birch, European White Betula pendula Roth
Birch, Gray Betula populifolia Marsh.
Birch, Paper (White) Betula papyrifera Marsh.
Birch, River Betula nigra L.
Birch, Sweet (Black, Cherry) Betula lenta L.
Birch, Yellow Betula alleghaniensis Britt.
Blackberry Rubus alleghaniensis Porter
Blackgum Nyssa sylvatica Marsh.
Blueberry Vaccinium Spp.
Boxelder Acer negundo L.
Catbrier Smilax glauca Walt.
Cherry, Black Prunus serotina Ehrh.
Chestnut, American Castanea dentata (Marsh.) Borkh.
Chestnut, Japanese Castanea crenata Sieb. & Zucc.
Chickweed Mouse-Ear Cerastium viscosum L.
Chinkapin, Allegheny Castanea pumila Mill.
Cottonwood, Black Populus trichocarpa T. & G.
Currant Ribes Spp.
Dogwood, Flowering Cornus florida L.
Douglas-Fir Pseudotsuga menziesii (Mirb.) Franco
Elm Ulmus Spp.
False-Toad-Flax Comandra umbellata (L.) Nutt.
Fern, Bracken Pteridium aquilinum (L.) Kuhn.
Fir, Balsam Abies balsamea (L.) Mill.
Fir, Bracted Balsam Abies balsamea Var. phanerolepis Fern.
Fir, Fraser Abies fraseri (Pursh) Poir.
Fir, Grand Abies grandis Lindl.
Fir, Noble Abies procera Rehd.
Fir, Silver Albies alba Miller
Fir, Subalpine Abies lasiocarpa (Hook.) Nutt.
Fir, White (Concolor) Abies concolor Lindl. & Gord.
Goldenrod Solidago Spp.
Gooseberry Grossularia Spp.
Grape, Muscadine Vitis rotundifolia Michx.
Grape, Northern Fox Vitis labrusca L.
Greenbrier Smilax rotundifolia L.
Hawthorn Crataegus Spp.
Hemlock, Eastern Tsuga canadensis Carr.
Hickory Carya Spp.
Honeylocust Gleditsia triacanthos L.
Horsechestnut Aesculus hippocastanum L.
Incense-Cedar Libocedrus decurrens Torr.
Labrador Tea Ledum groenlandicum Oeder.
Larch, Eastern (Tamarack) Larix laricina (Duroi) K. Koch
Larch, European Larix decidua Mill.
Locust, Black Robinia pseudoacacia L.
Maple, Red Acer rubrum L.
Maple, Silver Acer saccharinum L.
Maple, Sugar Acer saccharum Marsh.
Milkweed, Common Asclepias syriaca L.
Oak, Black Quercus velutina Lam.
Oak, Chestnut Quercus prinus L.
Oak, Pin Quercus palustris Muench.
Oak, Post Quercus stellata Wangenh.
Oak, Northern Red Quercus rubra L. Wangenh.
Oak, Scarlet Quercus coccinea Muench.
Oak, Southern Red Quercus falcata Michx.
Oak, Swamp White Quercus bicolor Willd.
Oak, Water Quercus nigra L.
Oak, White Quercus alba L.
Oak, Willow Quercus phellos L.
Peach Prunus persica Batsch
Pine, Austrian Pinus nigra Arnold
Pine, Eastern White Pinus strobus L.
Pine, Jack Pinus banksiana Lamb.
Pine, Loblolly Pinus taeda L.
Pine, Longleaf Pinus palustris Mill.
Pine, Mugo Pinus mugo Turra.
Pine, Pitch Pinus rigida Mill.
Pine, Pond Pinus serotina Michx.
Pine, Ponderosa Pinus ponderosa Laws.
Pine, Red Pinus resinosa Ait.
Pine, Sand Pinus clausa (Chapin.) Vasey
Pine, Scots Pinus sylvestris L.
Pine, Shortleaf Pinus echinata Mill.
Pine, Slash Pinus elliottii Engelm.
Pine, Table-Mountain Pinus pungens Lamb.
Pine, Virginia Pinus virginiana Mill.
Poison-Ivy Toxicodendron radicans (L.) Kuntze.
Poplar Popuius Spp.
Port-Orford-Cedar Chamaecyparis lawsoniana (A. Murr.) Parl.
Ragweed, Giant Ambrosia trifida L.
Raspberry Rubus occidentalis L.
Redbud, Eastern Cercis canadensis L.
Sarsaparilla Aralia nudicaulis L.
Sassafras Sassafras albidum (Nutt.) Nees
Sequoia Sequoia gigantea (Lindl.) Decne.
Spruce, Black Picea mariana (Mill.) B. S. P.
Spruce, Blue Picea pungens Engelm.
Spruce, Norway Picea abies (L.) Karst.
Spruce, Red Picea rubens Sarg.
Spruce, White Picea glauca (Moench) Voss
Sumac Rhus Spp.
Sweetgum Liquidambar styraciflua L.
Sycamore, American Platanus occidentalis L.
Tanoak Lithocarpus densiflorus (Hook & Arn.) Rehd.
Tree-Of-Heaven Ailanthus altissima (Mill.) Swingle
Tupelo, Water Nyssa aquatica L.
Walnut, Black Juglans nigra L.
Witch-Hazel Hamamelis virginiana L.
Yellow-Poplar Liriodendron tulipifera L.
Bioindicator Species
Ozone
Ash, White Fraxinus americana L.
Blackberry Rubus alleghaniensis Porter
Cherry, Black Prunus serotina Ehrh.
Dogwood, Flowering Cornus florida L.
Grape, Northern Fox Vitis labrusca L.
Milkweed, Common Asclepias syriaca L.
Pine, Eastern White Pinus strobus L.
Sassafras Sassafras albidum (Nutt.) Nees
Yellow-Poplar Liriodendron tulipifera L.
Sulfur Dioxide
Ash, Green Fraxinus pennsylvanica Marsh.
Ash, White Fraxinus americatia L.
Aspen, Bigtooth Populus gandidentata Michx.
Aspen, Quaking (Trembling) Popuius tremuloides Michx.
Birch, Gray Betula populifolia Marsh.
Birch, Paper (White) Betula papyrifera Marsh.
Birch, River Betula nigra L.
Birch, Sweet (Black, Cherry) Betula lenta L.
Birch, Yellow Betula alleghaniensis Britt.
Blackberry Rubus alleghaniensis Porter
Pine, Eastern White Pinus strobus L.
Pine, Jack Pinus banksiana Lamb.
Ragweed, Giant Ambrosia trifida L.
Raspberry Rubus occidentalis L.
Sarsaparilla Aralia nudicaulis L.
Sumac, Staghorn Rhus typhina L,
Fluorides
Blueberry Vaccinum Spp,
Boxelder Acer negundo L.
Catbrier Smilax glauca Walt.
Gladiolus Gladiolus Spp.
Grape Vitis Spp.
Greenbrier Smilax rotundifolia L.
Maple Acer Spp.
Peach Prunus persica Batsch
Pine, Eastern White Pinus strobus L.
Spruce, Blue Picea pungens Engelm.
Glossary
Abdomen - The third or posterior major division of the insect body; consists normally of nine or ten
apparent segments; bears no functional legs in the adult stage, but may bear prolegs or false legs in the
larval stage.
Abiotic Pathogen - A nonliving, disease-causing entity, e.g., drought, salt, air pollutants.
Acute injury - Injury, usually involving necrosis, which develops within several hours to a few days after a
high dose exposure to a pollutant; expressed as fleck, scorch, bifacial necrosis, etc.
Aecial Stage (Aecium) - A spore stage of the rust fungi; a cuplike structure bearing aeciospores.
Alternate Host - One of two taxonomically different hosts required by a heteroecious rust fungus to
complete its cycle; also applies to some insects.
Anterior - In front; before; opposite of posterior.
Anthocyanosis - Presence of abnormal red-purple coloration in foliage.
Asexual Stage - Vegetative; without sexual organs or spores.
Autoecious - Completing entire life cycle on one host; especially applied to the rust fungi.
Banding - A foliar symptom characterized by a limited zone of necrotic or discolored tissue traversing
the leaf, e.g., the band of tissue on a pine needle injured by s02 or 03.
Basidial Stage (Basidium) - A spore stage of the rust fungi; a specialized structure in the basidiomycetes
bearing basidiospores.
Basidiocarps - Sexual fruiting structure in the basidiomycetes; conks, sporophore, mushrooms, etc.
Bifacial Necrosis - Death of plant tissues, extending from the upper to the lower leaf surface.
Bioindicator Species - Species, varieties, or cultivars sufficiently sensitive to a specific pollutant to be
useful as indicators for the presence of that pollutant.
Biotic Pathogen - A living organism capable of inciting disease, e.g., fungi, bacteria, viruses, etc.
Bleaching - Loss of normal color, tending toward white, cream, or tan coloration.
Blight - A common term for several different diseases; usually applied to those where leaf damage is
sudden and severe.
Bronzing - A golden brown discoloration that usually appears on the lower surface of leaves and is often
an advanced stage of the silvering or glazing typical of injury by pan and other oxidants; brown
coloration on needles due to spider mite infestation.
Callus Tissue - A protective tissue of thin-walled cells developed on wound surfaces, often beginning at
the edges of a wound.
Canker - A plant disease symptom characterized by a sharply defined necrosis of cortical tissue, often
sunken below bark surface.
Chewing Insects - Insects that consume all tissues of leaves or portions of leaves, using robust mandibles
for chewing.
Chlorosis - Yellowing of plant tissue due to failure of chlorophyll synthesis or to chlorophyll destruction.
Chlorotic Dwarf - An abiotic disease of pinus strobus characterized by reduced growth, chlorosis and
mottling of the needles, and premature abscission of all but current needles.
Chronic Injury - Injury which develops after long-term or repeated low dose exposure to an air pollutant;
expressed as chlorosis, bronzing, premature senescence, reduced growth, etc.
Clonal Lines - A group of plants originating from buds or cuttings from the same individual.
Conk - The fruiting structure of a wood-rotting fungus, especially of one of the polyporaceae.
Cocoon - A covering, composed partly or wholly of silk or other sticky fiber, spun or constructed by many
larvae as a protection for the pupal stage.
Cornicles - The posterior dorsal erect or semi-erect tubules of aphids which secrete a waxy defensive
liquid to protect the insect against enemies; short, blunt horns or rounded projections occurring on the
abdomen.
Crawler - The first instar motile nymphal stage of scale insects and mealybugs, which moves to a new
feeding site before settling down to a sessile existence for the rest of its developmental life.
Crinkling - Bending or twisting of foliage without breaking; wrinkling.
Cryptic - Hidden or concealed.
Defoliator - Any chewing insect that consumes the leaves or needles of plants.
Deliquescent - To ramify into fine divisions, such as abnormal numbers of buds, twigs, branches, or
leaves, e.g., witches' broom development.
Dorsal - Of or belonging to the upper surface; top.
Dorsoventral - From top to bottom; from the upper surface to the lower surface.
Dorsum - The upper surface; top.
Dose - A measured concentration of a toxicant for a known duration of time (concentration per unit
time).
Egg Gallery - A long, narrow tunnel along the sides of which eggs are deposited in small niches; the
pattern of construction is often diagnostic of a particular species of insect.
Egg Mass - Cluster of eggs, usually in a matrix of body hairs or wing scales from the female adult and/or
a mucilaginous cementing secretion.
Elytra - The anterior leathery or chitinous wings of beetles and leafhoppers; serve as coverings to the
hind wings and commonly meet at rest in a straight line down the middle of the dorsum.
Engraver - Beetle which feeds in the phloem-cambium region of woody plants, often scoring or
engraving adjacent sapwood tissues.
Epicormic Branching - Branches arising from buds in bark along mainstem, most commonly occurring in
trees under crown stress; also called watersprouts.
Epidemic - A change, usually a sudden increase, in a disease within a population.
Forewings - Front pair of wings.
Fleck - White to tan necrotic lesions up to a few millimeters in length or diameter, usually confined to
the upper surface of leaves.
Frass - Solid larval insect excrement; mixed with wood fragments in woodboring or bark-boring insects.
Fruiting Body - A specialized structure, often macroscopic, on or in which spores are produced.
Fumigation - The natural or controlled exposure of plants to toxic gases or volatile substances.
Gall - A swelling or outgrowth of tissue induced by a pathogen or insect on a plant.
Generation - The successive developmental stages from reproduction to reproduction, e.g., egg, larva,
pupa, adult.
Girdling - Destruction of tissue in a ring around a twig, branch, or stem.
Gout - Formation of swellings at nodes or at the base of buds.
Gregarious - Living in groups or communities.
Grub - An insect larva; a term loosely applied, usually to larvae of coleoptera; larva is thick-bodied with
well-developed thoracic legs but no abdominal prolegs.
Heteroecious - Requiring two taxonomically different hosts to be able to complete the entire life cycle,
as in the rust fungi.
Honeydew - A sweetish excretion produced through the anus by certain insects, notably aphids and
scale insects.
Host - A living organism serving as a food source for a parasite.
Itysterothecium - A sexual fruiting structure of the ascomycete fungi, usually football-shaped or
elongate in appearance and occurring on infected needles.
Instar - The insect itself during the time between molts in the larva or nymph, numbered to designate
the various periods; i.e., the first instar is the insect between the egg and first molt.
Interveinal - Between veins.
Intraveinal - Associated along or within veins.
Larva (plural= larvae) - The immature instars, between the egg and pupal stages, in an insect having a
complete metamorphosis (egg, larva, pupa, adult). Larvae feed and grow but cannot fly, nor can they
reproduce.
Lesion - A wound; a well-marked, but limited, diseased area; a break or rupture through a tissue,
especially a surface tissue.
Looper - A caterpillar in which some or all of the middle abdominal prolegs are wanting and which
moves by placing the posterior part of the abdomen next to the thorax, forming a loop of the
intervening segments, then extending the anterior part of the body forward.
Middorsal - In the middle of the upper side or dorsum.
Mimicking Symptoms - Symptoms similar to those caused by pollutants but induced by other abiotic or
biotic causal agents.
Miner - The larval stage of an insect which makes galleries or burrows between the upper and lower
surfaces of leaf tissue.
Mite(s) - Small, often minute, arthropods in the order acarina of the class arachnicla, which includes
spiders, scorpions, and related forms. Mites have four pairs of legs vs. Three pairs in insects.
Molt - To cast off the outgrown skin or cuticle in the process of insect development; changing from one
instar to the next.
Mottle - Irregular, diffuse patterns of chlorotic areas interspersed with normal green leaf tissue.
Mosaic - A diseased condition where different portions of a leaf vary in amounts of chlorophyll, thus
giving the leaf a mottled appearance; usually caused by viruses.
Mycelium - A mass or aggregate of hyphae, vegetative stage of fungi.
Naked - Larva devoid of body hairs or setae; pupa not enclosed in a cocoon or other covering.
Necrosis - Death.
Nymph - The immature stage of insects, following hatching, which does not have a pupal stage, i.e.,
incomplete metamorphosis (egg, nymph, adult). Late instar nymphs may have nonfunctional
rudimentary wings and/or genitalia.
Oviposition - The act of depositing the eggs.
Ovipositor - The egg-laying apparatus; the extended genitalia of a female insect.
Parasite - An organism which lives on or in another living organism and obtains part or all of its nutrients
from that other living organism.
Pathogen - Any agent of the environment capable of inciting disease.
Perithecium - A sexual fruiting structure of the ascomycetes with an opening called the ostiole at or near
its top.
Posterior - Hind or hindmost; opposite of anterior.
Predisposition - The weakening of an organism by some factor(s) of either the physical or biotic
environment so as to render the organism more susceptible to a pathogen.
Proleg - Any process or appendage that serves the purpose of a leg; specifically, the fleshy, unjointed,
ventral abdominal projections of caterpillars and certain sawfly larvae.
Pupa - The resting, inactive, nonfeeding instar in all holometabolous insects; the stage intermediate
between the larva and the adult.
Pycnial Stage (pycnium) - A flaskshaped spore stage of the rust fungi; oozes out spores in a sticky matrix.
Pycnidium - An open-pored, flaskshaped fruiting structure in which asexual spores called coniclia are
produced.
Rasping - A type of feeding by insects which rub or grate the leaf surfaces with their mouthparts to
obtain particles for consumption.
Resinosis - Resin flow through bark or from wounds or cankers on conifers.
Rhizomorph - A thread- or cord-like fungal structure made up of hyphae.
Ringshake - Peripheral cracks in woody tissues of stems. The pattern of damage is concentric with the
annual rings.
Ringspot - A circular area of chlorosis with a green center.
Saprophyte - An organism living on dead organic matter.
Scorch - Appearing as if tissues were burned by heat; usually affecting marginal portions of leaves.
Senescence - Aging of tissues; growing old.
Sessile - Attached or fastened; incapable of moving from place to place.
Seta (plural = setae) - Slender, hairlike or bristly projections arising from the epidermal layer on any part
of the body of an insect.
Sexual Stage - Reproductive stage of the life cycle of an organism.
Shotholes - Small holes in a leaf caused by feeding activity and giving the appearance of injury via a
shotgun.
Sign - The actual presence of the causal organism in association with the disease symptoms.
Skeletonizer(s) - Insects which consume leaf tissue, often from the lower side of the leaf, leaving the
upper epidermis and vascular tissues intact.
Spore - A specialized structure consisting of one or few cells and serving any or all of the following three
functions: (i) reproduction, (ii) dissemination, (iii) survival.
Sporophore - A spore-producing or supporting structure.
Stadium (plural = stadia) - The period of time between two successive molts.
Stage - One of the successive principal divisions in the life cycle of an insect, e.g-, egg, nymph, larva,
prepupa, pupa, adult.
Staghead - Death of limbs and main branches of a tree in the upper crown, giving the appearance of
antlers.
Stipple - Pigmented spots up to a few millimeters in diameter, often on the upper surface of leaves.
Stylet - A small, stiff, needlelike tube inserted into a food source to obtain liquid food.
Sucking Insects - Insects that insert their mouthparts into plant tissues and withdraw nutrients and fluids
through stylets.
Suscept - Any organism that can be attacked by a biotic pathogen.
Symptom - Visible or measurable manifestation that an organism is diseased; a change in the organism
itself.
Telial Stage (telium) - A stage of the rust fungi; a fruiting structure usually appearing as fine, hairlike
projections from lower surfaces of infected leaves.
Thoracic - Belonging or attached to the thorax.
Thorax - The body region behind the head, which bears wings and true (jointed) legs if present.
Tuft - Bunching of twigs or needles.
Tylosis - Outgrowth of a cell membrane from a ray or axial parenchyma cell through a pit in a xylem
vessel wall into the vessel, partially or completely blocking the lumen of the vessel.
Uredial Stage (uredium) - A stage of the rust fungi; a fruiting structure usually appearing as a pustule
bearing the repeating spore stage that leads to disease increase.
Water-soaked - A dull green coloration of diseased tissues due to membrane leaking of cellular contents
into intercellular spaces.
Wilt - A common symptom of disease due to a loss of turgor and resulting in subsequent drooping and
collapse of the foliage or succulent tissues.
Witches' Broom - A massed proliferation of the branches of a woody plant.
Zone Line - Narrow brown or black lines In Decayed Or Decaying Wood.
Selected References
Air Pollutants
Jacobson, J. S., And A. C. Hill, Eds.
1970. Recognition Of Air Pollution Injury To Vegetation: A Pictorial Atlas. Pittsburgh: Air Pollution
Control Association.
Malhorta, S. S., And R. A. Blauel.
1980. Diagnosis Of Air Pollutant And Natural Stress Symptoms On Forest Vegetation In Western Canada.
Edmonton, Alberta: Northern Forest Research Center Information Report Nor-X-228.
Ormrod, D. P.
1978. Pollution In Horticulture. Amsterdam: Elsevier Scientific Publishing Co.
Skelly, J. M., S. V. Krupa, And B. E. Chevone.
1979. "Field Surveys." In Handbook Of Methodology For The Assessment Of Air Pollution Effects On
Vegetation, Edited By W. W. Heck, S. V. Krupa, And S. N. Linzon. Pittsburgh: Air Pollution Control
Association.
Skelly, J. M., And R. C. Lambe.
1974. Diagnosis Of Air Pollution Injury To Plants. Blacksburg, Va.: Virginia Polytechnic Institute And State
University, Cooperative Extension Division Publication 568.
U.S. Department Of Agriculture, Forest Service.
1973. Air Pollution Damages Trees. Upper Darby, Pa.: State And Private Forestry.
U.S. Environmental Protection Agency.
1976. Diagnosing Vegetation I Injury Caused By Air Pollution. D. R. Hicks, Project Officer. Research
Triangle Park, N.C.: Office Of Air Quality Planning And Standards. Usepa Contract No. 68-02-1344.
Van Haut, H., And H. Stratmann.
1970. Farbtafelatlas Fiber Schwefeldioxidwirkungen An Pflanzen. [Colorplate Atlas On The Effects Of
Sulphur Dioxide On Plants.] Essen, Germany (F.R.): Verlag W. Firardet.
Diseases
French, D. W. Et Al.
1975. Diseases Of Forest And Shade Trees. St. Paul, Minn.: Univ. Of Minnesota Department Of Plant
Pathology.
Hepting, G. H.
1971. Diseases Of Forest And Shade Trees Of The United States. U.S. Department Of Agriculture, Forest
Service Handbook 386.
U.S. Department Of Agriculture, Forest Service.
1980. Forest Insect And Disease Handbook: Renewable Resources Evaluation. U.S. Department Of
Agriculture, Forest Service, Southeastern Area General Report Sa- Gr 14.
U.S. Department Of Agriculture, Forest Service.
Forest Pest Leaflet Series. This Series Covers Diseases And Insects And Is Available From The Respective
U.S. Department Of Agriculture, Forest Service, Forest Pest Management Offices.
U.S. Department Of Agriculture, Forest Service,
1985. Insects And Diseases Of Trees In The South. Atlanta, Ga.: U.S. Department Of Agriculture, Forest
Service, Southern Regional General Report R8-Gr5
U.S. Department Of Agriculture, Forest Service.
1980. Oak Pests: A Guide To Major Insects, Diseases, Air Pollution, And Chemical Injury. Stoneville, Miss.:
U.S. Department Of Agriculture, Forest Service, Southern Forest Experimental Station General Report SaGr 11.
Insects
Anon.
1979. A Guide To Common Insects And Diseases Of Forest Trees In The Northeastern United States.
Available From: U.S. Government Printing Office, Washington, D.C.; Fidm Na-Fr4.
Borror, D. J., And R. E. White.
1970. A Field Guide To The Insects Of America North Of Mexico. Peterson Field Guide Series. Boston:
Houghton Mifflin Co.
Doane, C. C., And M. L. Mcmanus, Eds.
1981. The Gypsy Moth: Research Toward Integrated Pest Management. U.S. Department Of Agriculture,
Technical Bulletin 1584.
Johnson, W. T., And H. H. Lyon.
1976. Insects That Feed On Trees And Shrubs. Ithaca, N.Y.: Cornell University Press.
Martineau, R.
1984. Insects Harmful To Forest Trees. Ottawa: Multiscience Publishers, Ltd,
Rose, A. H., And O. H. Lindquist.
1973. Insects Of Eastern Pines. Department Of The Environment, Canadian Forest Service, Publication
1313.
_________
1977. Insects Of Eastern Spruce, Fir, And Hemlock. Department Of The Environment, Canadian Forest
Service, Forest Technical Report 23.
_________
1980. Insects Of Eastern Larch, Cedar, And Juniper. Department Of The Environment, Canadian Forest
Service, Forest Technical Report 28.
_________
1982. Insects Of Eastern Hardwood Trees. Department Of The Environment, Canadian Forest Service,
Forest Technical Report 29.
Sanders, C. I. Et Al., Eds.
1985. Recent Advances In Spruce Budworms Research. Ottawa: Canadian Forest Service And U.S.
Department Of Agriculture.
Thatcher, R. C. Et Al., Eds.
1980. The Southern Pine Beetle. U.S. Department Of Agriculture, Technical Bulletin 1631.
U.S. Department Of Agriculture, Forest Service.
Forest Pest Leaflet Series. This Series Covers Diseases And Insects And Is Available From The Respective
U.S. Department Of Agriculture, Forest Service, Forest Pest Management Offices.
U.S. Department Of Agriculture, Forest Service.
1985. Insects Of Eastern Forests. Miscellaneous Publication 1426.
U.S. Department Of Agnculture, Forest Service.
1980. Oak Pests. A Guide To Major Insects, Diseases, Air Pollution, And Chemical Injury. Stoneville, Miss.:
U.S. Department Of Agriculture, Forest Service, Southern Forest Experimental Station General Report SaGr 11.
Wilson, L. F.
1977. A Guide To Insect Injury Of Conifers In The Lake States. U.S. Department Of Agriculture,
Agricultural Handbook 501.
Photographic Credits
Many of the photographs presented within this manual were taken by the contributing authors and/or
the Editorial Review Team. Gratitude is also expressed to the following contributors:
Canadian Forestry Service
Chemlawn Corporation (D. Shetlar)
Florida Department Of Agriculture, Forestry Division (E. Barnard)
Pennsylvania Department Of Environmental Resources, Bureau Of Forestry
(G. Hoover, B. Towers)
Pennsylvania State Agricultural Experiment Station, The Pennsylvania State University
(C. L. Adler, P. Heller, D. Karasevicz, L. Kuhns, L. Nichols, N. Wenner)
Southern Forest Insect Work Conference (Various Members)
United States Department Of Agriculture, Forest Service
M. Mielke, I. Millers, M. Ostry, D. Skilling)
United States Department Of The Interior, National Park Service (C. Eager)
United States Environmental Protection Agency
University Of Florida, School Of Forest Resources (G. Blakeslee)
University Of Minnesota, Department Of Plant Pathology (D. French)
Virginia Division Of Forestry (C. Morris)
Cover Photos: Grant Heilman
This Publication Was Produced By Agricultural Information Services, College Of Agriculture, And The
Department Of Plant Pathology, The Pennsylvania State University, For The USDA-Forest Service.
Copyeditors: Laverne M. Maginnis Tanya Spewock Designer: James Mcclure Typist: Brenda Holcomb
Insects
Pesticides And The Sugar Maple Industry
Extension
Maple Syrup Digest
Gordon R. Nielson, Extension Entomologist, University of Vermont, Burlington, Vt.; H. Brent Teillon ,
Chief, Forest Resource Protection, State of Vermont, Department of Forests and Parks, Montpelier, Vt.
Vol. 13, No.3
October 1974
REF# 065
There are a number of insects that attack northern hardwood trees, including sugar maples. These
include the saddled prominent, gypsy moth, forest tent caterpillar, and fall cankerworm. Insecticides
such as carbaryl (Sevin) are effective against them. But maple sugar producers are engaged in the
production of a food product and are therefore forbidden by law to use these substances.
Pesticide use on food commodities has been regulated for decades. Until recent years, the fact that a
food product is derived from many maple trees had apparently escaped the notice of pesticide
regulatory officials. However, the public has become very much aware and concerned about the use of
any chemical in food production and processing. Too, new Federal and state laws have been passed
clarifying legal pesticide uses and establishing strong penalties for pesticide misuse. Thus, the situation
regarding pesticide use in the sugar maple food industry has developed into a difficult problem.
Recent statutes and regulations have made some former practices in and around food production and
food processing areas, including maple, illegal or strongly inadvisable. By law, there are only two
pesticide uses permitted in the production and processing of maple food products. These are the use of
paraformaldehyde pellets in the taphole, and the use of certain disinfectants as sodium hypochloride,
for sanitizing "food-processing" equipment.
The use of insecticides, fungicides, herbicides, rodenticides or any pesticides other than the two
mentioned above in sugarbushes, or on and around maple trees to be tapped, is not permitted under
Federal law. Doing so could constitute a "use inconsistent with the label" and be considered both a civil
and a criminal act.
Tapping trees that have been previously treated or are growing in an area that has been treated with
pesticides for insect, disease, weed, or rodent control maybe a risky business. While a number of
pesticides are registered for use on trees, none are presently cleared for use on maples being, or to be,
used to produce food. Maple products from areas subject to spray drift from any pest or weed control
operation could contain illegal pesticide residue and be subject to seizure and destruction as
adulterated foods.
Tolerances Are Needed
A number of insecticides are effective against maple pests in northern hardwood forest and shade tree
situations. But, it has not been proven that any of these compounds applied to maple trees will not
appear in the sap and syrup from the sprayed trees.
Before any pesticide can be cleared for use on a maple food crop, a tolerance amount for that chemical
must be established. (This is the legal amount that may be present in the food.) Any food product with a
greater amount, or for that matter, any measurable amount of a pesticide lacking a legal tolerance
would be considered adulterated. Tolerances are set by the Environmental Protection Agency (E.P.A.)
based on evaluation of residue studies on the specific crop commodity concerned.
How Do We Do This?
The candidate pesticide must be applied to the trees at normal and greater than normal rates. Sap must
be collected from treated trees periodically during the sugaring season. Analyses of pesticide residues
must be made in the sap, syrup, and sugar. If the chemical does not appear in the product, or appears at
levels below those considered hazardous to human health, the establishment of a tolerance could be
anticipated.
We Are Doing It!
The U. S. Forest Service, Vermont Departments of Agriculture and Forests and Parks, and the University
of Vermont are currently involved in limited experiments to provide data leading to establishment of a
tolerance for insecticide in maple products (fig. 1). Carbaryl has been selected as the candidate
insecticide to be used in the initial chemical residue studies because of its wide usage and its suitability
for controlling the insects that are potentially a threat to sugar maples.
Figure 1. Researchers load crop spraying plane with Sevin, an insecticide being tested for possible use
on maple trees in sugarbushes.
Carbaryl was applied to sugarbushes in the U. S. Army Test Firing Range at Underhill, Vermont, in the
spring and summer of 1974. The insecticide was applied at once, twice, and five times the normal rate.
Two formulations of carbaryl were applied: Sevin 80 Sprayable and Sevin 4 Oil. During the 1975 sugar
season samples of sap will be collected from all sprayed plots and sap, syrup, and sugar will be analyzed
for residues of carbaryl. Samples of sap from an unsprayed plot will also be taken and used for
comparison.
Progress Towards Integrated Pest Management In Sugar Maple Stands - Is it simple to manage sugar
maple insect pests
Extension
Maple Syrup Digest
Bruce L. Parker, Margaret Skinner & Michael Brownbridge, Entomology Research Laboratory, University
of Vermont, Burlington, Vermont
Vol. 5A, No. 4
December 1993
REF# 225
It is not a simple matter to protect the health of sugar maple trees yet it is absolutely essential that you,
the sugarmaker, keep in. mind that it should receive the highest of priorities. REALLY—if we can't
protect our trees—if they become weakened, stressed and eventually show signs of severe dieback and
mortality sets in— FORGET SUGARING.
Did you know that there are more than 150 different insects that feed on sugar maple? Just think ... 150
different species each acting and interacting in a slightly different way. It is no wonder that scientists
and pest managers have such a hard time developing management strategies that are practical,
economical and socially acceptable. We are lucky though - only about 8% of the insect species feeding
on sugar maple can be considered real bad actors.
Here at our laboratory we are working hard to develop an environmentally safe, useable method to
manage pear thrips, maple leafcutter and maybe even gypsy moth in your stands. With financial
assistance from the North American Maple Syrup Council our research on the use of fungal pathogens
for control of these pests is progressing rapidly. This past summer we field tested some of these fungi in
sugarbushes located in central Vermont. The fungi were formulated as wettable powders, emulsifiable
concentrates and granular materials and applied to small experimental plots. Our efforts were
concentrated on how they worked against maple leafcutter and pear thrips. Although we used one
application rate, we did make our applications at several different times during the growing season.
Studies on the persistence of the fungal formulations in forest soils were also started.
Although data are still being taken from the forest, it appears as though at least partial success was
obtained. Of the three different fungal pathogens that we tested, our Verticillium strains (prepared as
wettable powders) were the most effective in reducing populations of maple leafcutter. The very same
Verticillium strains were also effective against pear thrips in our laboratory trials. You know, Rome
wasn't built in a day and we didn't expect to provide all the answers in just one season. Next year our
formulations will be modified and application timing and rates adjusted to improve our results.
Based on your suggestions we are now beginning experiments to determine the impact of our fungal
materials on non-target organisms. This exciting aspect of our work will facilitate later product
development. We have initiated cooperation with the Environmental Protection Agency (EPA) and they
are most interested in our biological control research. Our goal is to develop a holistic and sustainable
strategy for managing insect pests of sugar maple. Results of our field trials indicate that this goal can be
reached in the very near future.
Sugar Maple IPM Vermont Leads The Way
Research
Maple Syrup Digest
Bruce L. Parker, Margaret Skinner & Michael Brownbridge, Entomology Research Laboratory, University
of Vermont
Vol. 5A, No. 1
February 1993
REF# 221
Update 1993: Integrated Pest Management (IPM) is one of the major thrusts of scientists at the
Entomology Research Laboratory at the University of Vermont. Several major projects, in part funded by
the North American Maple Syrup Council, are being done on various aspects of maple leaf cutter and
pear thrips management.
Pear thrips, an ever present threat to sugar maple trees, appears to be highly susceptible to fungal
pathogens. These pathogens have been isolated and further tested under laboratory conditions. We
have selected two of the most promising isolates and they are now being evaluated for mass-culturing.
Once this is completed they will be formulated to enable us to conduct small-scale pilot tests in
sugarbushes in the spring. Our plans are to apply these pathogens, which are harmless to trees and
humans, to the soil. Because pear thrips and also maple leafcutter come in contact with the soil or litter
on the forest floor, we anticipate excellent control of these pests.
This research is a new approach to pest management in a forest. It will result in minimal impact on the
environment and eliminate worries about the use of pesticides. The pathogenic fungi occur naturally
and we are merely enhancing Nature's ability to control and manage itself. Of interest is the fact that
the Vermont isolates we are testing are also effective against gypsy moth. This insect which causes
major defoliation to many of our valuable forest trees is soon to be joined by another close relative, the
Asian gypsy moth. This Asian form has recently been discovered on the West Coast and who knows how
quickly it will spread to our forests. Perhaps our fungi may be effective against this new threat.
The new method is based on the fact that pear thrips will emerge from the soil if we just take our soil
samples and put them at room temperature at the proper time. We will devise a method to trap and
count the emerging insects. It is our goal to have this procedure available for all sugarmakers to use in
the fall of 1993.
Because thrips are becoming more and more troublesome with agricultural crops in general we are
hosting a major conference in Burlington in September. The 1993 International Conference on
Thysanoptera: Towards Understanding Thrips Management will attract scientists, pest managers and
growers from throughout the world to discuss the current methods and strategies for control of these
tiny pests. Additional information about this international event may be obtained by writing to the
authors at 655B Spear Street, S. Burlington, Vermont 05403.
Sugar Maple IPM - An Update From Vermont
Extension
Maple Syrup Digest
Bruce L. Parker, Margaret Skinner & Michael Brownbridge, Entomology Research Laboratory University
of Vermont
Vol. 4A, No. 3
October 1992
REF# 214
It seems as though sugar maple trees are prone to every type of damage imaginable. If it isn't air
pollution, it's some canker. If it isn't a porcupine then it's bark splitting because we drove the spouts into
frozen bark. Yesterday, it was forest tent caterpillar and today, it is maple leafcutter and pear thrips. It is
just not simple to manage a sugar maple stand especially when there are so many impacts.
Sure you can manage the porcupine and you can make sure that the spouts go in at the right time. But
what do you do about the chronic insect problems? How do you manage maple leafcutter, forest tent
caterpillar or pear thrips?
The use of agricultural chemicals should not be discounted but few, if any, are now available for the
sugarmaker to use. Most sugarmakers really don't want to use them anyway. There has to be a better
way and IPM, integrated pest management, is the strategy for the future. One part of this process
involves the use of natural en emies to maintain pest populations at an acceptable level.
The NAMSC has supported research at the University of Vermont on the use of fungal pathogens for
management of pear thrips. Several very effective fungi have been discovered that appear to be useful
on a practical basis in sugarbush IPM. Of major interest is that these natural enemies are harmless to
sugar maple trees, other plants and to humans. They have great potential for controlling many of the
major defoliators that seriously impact maple trees. They have unique characteristics that make them
particularly suitable for persisting in a forest and giving us long-term management. We found them in a
forest habitat and that is where they will be used.
During the last several months researchers have been able to select several fungal pathogens from a
broad range of material. Those selected show the greatest potential for development and will now be
formulated for easy application to the forest floor. The next step will be a small pilot test to be
conducted in sugarbushes in central Vermont in 1993. We know from our laboratory studies, that they
are effective against maple leafcutter, gypsy moth and pear thrips. Now we need to determine if they
are effective against these pests in a forest situation. After this is completed plans will be made to test
them on a large-scale basis in forests in Vermont and Connecticut.
Figure 1. Sugar maple leaves damaged by maple leafcutter and pear thrips.
Lewis Maple Producers Spray To Control Caterpillar Pest
Extension
Maple Syrup Digest
Bette Schoff, Watertown Daily Times supplied the photographs and allowed reprinting of the article.
Vol. 8, No. 3
October 1969
REF# 104
Saddled Prominent Caterpillars.... quite an impressive name for a killer: a small pest causing maple
producers plenty of concern as well as the possibility of financial losses if defoliation and possibly the
death of the sap bearing trees should result.
Lewis County, tops in maple production in the State, has started to take the "prominence" out of the
caterpillar and in its fight has lined up a capable and determined task force to do the job.
The "crew" includes members of the Cooperative Extension Service, the State Conservation Department,
and, of course, those most personally affected, the maple producers themselves.
C.F. (Neil) Handy, Cooperative Extension chief, provides a look into the back ground of the problem in an
excerpt from an article he wrote last year for the National Maple Syrup Digest:
"During July and August of 1968, saddled prominent caterpillars attacked more than 100,000 forest
acres in Lewis County.
"They were identified as feeding on maples a year earlier in the Belfort area. The infested area at that
time was confined to about 200 acres and the caterpillars were nearing the end of their feeding cycle. It
was in this area that a great saddled prominent moth population explosion was noted during April and
May of 1968. Each female moth is capable of laying from four to six hundred eggs. Eggs are laid singly on
leaves, hatch in about eight to ten days, the young larvae appear, feed on the leaves of both maple and
beech, molt four times, becoming full grown during late July or early August.
"Then they crawl down the trunk or drop to the ground and fashion silk lined pupal cells in the lower
moist layers of leaf mold or in the upper layer of soil, in which they pupate and spend the winter.
"More than 2,000 acres of maples were sprayed from the air during the last three weeks of July and first
two weeks of August. Sugar bushes that were sprayed when feeding was first observed remained green
with dense foliage. Where no spraying was done, caterpillars stripped all the foliage from the trees in
infested areas.
"The infestation in Lewis County starting with 200 acres in 1967 and spreading to more than 100,000
acres in 1968, was of grave concern to maple producers."
Figure 1. William Rockwell and Bruce S. Schneider of the New York State Conservation Department
check the map of the area to be sprayed.
Figure 2. Gerald Lyndaker, on whose farm this particular flight was originating; Clifford Hebdon, an area
foreman of the Department, and C.F. (Neil) Handy, county extension agent, discuss last minute details.
Figure 3. The "chopper" returns for another load of spray. Two thousand acres were sprayed in 1968.
Action Is Taken
Mr. Handy said that following these observations, the Lewis County Board of Supervisors was
approached and, with the District and Forest Practice Board, petitioned the New York State
Conservation Department to initiate, compile and present plans for controlling "this pest that threatens
the maple, forest and tourism industries in the area".
The state obliged and agreed to a share cost program (with maple producers) for spraying areas in
danger of infestation.
A survey was made to determine these blighted areas and this year 99 per cent of the producers in need
agreed to share cost for spraying. A total of 4,000 acres will be treated and the operation is
extraordinary in its precision planning.
Clifford Hebdon, area foreman for the Conservation Department's Forest Pest and Disease Control
program, is the boss "on the ground", (although he is noted for his daring tree climbing to place balloon
markers above the tree tops for aerial identification.)
"Cliff" has detailed area maps, and air to ground walkie-talkies enable him and his men to guide the
"boss in the air," helicopter pilot, former Navy Lt. Cmdr. Amsden, "Ace" Howland, and his co pilot, Bill
Krom.
Figure 4. The aerial spraying is in progress.
Spraying Carried Out
This writer, on hand for spraying operations at the Gerald Lyndaker property, arrived in time for the first
spray run of the day. An early morning fog had postponed the usual 4 or 5 a.m. starting time, so take off
was nearer 9 a.m. (Because of atmospheric conditions, spraying must be done in the early morning
hours and is usually completed before 11 a.m.)
"Ace" came whirling in with an unexpected turbulence into the open field, (unexpected, that is, to this
lone female who in a split second was sporting a Phyllis Diller hairdo). Ralph M. Pettit, Times Chief
photographer, appeared unruffled and nary a hair blew as he placidly "shot" the helicopter in action.
Neil Handy, our guide for the trip, was perfectly at case with the situation very familiar to him.
The instant the chopper landed, "Cliff's" crew, operating much like a volunteer fire department in drill
competition, charged with hoses from a nearby truck and filled the spraying tank with the caterpillar's
death potion. The mixture includes 1¼ (one and one fourth) pounds of "sevin" to a gallon of water, plus
4 ounces of "pinolene," an extender which helps make the solution "stick" to the foliage. A gallon of the
formula is used per acre and costs over a dollar per pound.
DDT is a "naughty" word in the North Country, and although it costs a great deal less than sevin, is not
used since the cost could be greater from the standpoint of detrimental effects on fish and game so
highly regarded in our area.
Within a matter of three or four minutes, "Cliff's" men had filled the tank and "Ace" was off with a roar
to the designated position, returning for the same quickie refills each time the supply was depleted.
This time I was more prepared for the sweep of air and took cover in a car. As I peered around me after
the take off," there was photographer Pettit still calmly getting "ground to air" shots, Neil Handy was
still explaining the hazards of the "prominent caterpillar" to yours truly, and probably the most
unconcerned spectator of all, young Gerry Lyndaker, remained busy at routine tractor work in the field,
never bothering to look "up" at all.
Saddled Prominent Caterpillar Threatens Maples
Extension
Maple Syrup Digest
C.F. Handy, Cooperative Extension Agent, Lowville, N.Y.
Vol. 7, No. 4
December 1968
REF# 117
Sugar maples in Lewis County encountered a severe infestation of saddled prominent caterpillars that
attacked more than 100,000 forest acres during July and August of 1968.
Saddled prominent caterpillars feeding on maples were identified a year earlier in the Belfort area. The
infested area at that time was confined to about 200 acres and the caterpillars were nearing the end of
their feeding cycle. It was in this area that a great saddled prominent moth population explosion was
noted during late April and May of 1968. Each female moth is capable of laying from 400 to 600 eggs.
Eggs are laid singly on the leaves, hatch in from 8 to 10 days, the young larvae appear, feed on the
leaves of both maple and beech, molt four times, becoming full grown during late July or early August.
They then crawl down the trunk or drop to the ground and fashion silk lined pupal cells in the lower
moist layers of leaf mold or in the upper layer of soil, in which they pupate and spend the winter.
More than two thousand acres of maples were sprayed from the air during the last three weeks of July
and first two weeks in August. Sugar bushes that were sprayed when feeding was first observed
remained green with dense foliage. Where no spraying was done, caterpillars stripped all the foliage
from the trees in infested areas.
The infestation in Lewis County, starting with 200 acres in 1967 and spreading to more than 100,000
acres in 1968, is a matter of grave concern for maple producers. In Lewis County, both the Lewis County
Board of Supervisors and the District and Forest Practice Board have petitioned the New York State
Conservation Department to initiate, compile, and present plans for controlling this pest that threatens
the maple, forest and tourism industries of this area.
That maple defoliation can cause severe losses to maple producers is evidenced by a Pennsylvania study
that shows defoliation can result in death of about 30% or more of the trees. Studies in eastern New
York by Robert Sweet of the Conservation Department, show a reduction of 30% or more in the
sweetness of sap when the forest tent caterpillar defoliated maples.
Maple producers in Lewis County are looking forward to 1969 with full realization that saddled
prominent moths will be back laying more eggs next spring to hatch into more caterpillars. Producers
expect to spray again if an infestation threatens but will be expecting some form of financial assistance
from the State Conservation Department.
Figure 1. Ground view of sprayed area (left) and unsprayed area (right) along a roadway in Croghan area.
Figure 2. The culprit. The saddled prominent larvae crawling on a beech tree. Beech and maple, chief
components of the sugar woods in New York are favorite host species of this insect.
Figure 3. Aerial photo of road in ground view (photo 1). Sprayed area in left foreground has normal
foliage; hardwoods in rest of photo are completely defoliated as is the brush and ground cover.
Fungus That Slaughters Gypsy Moth Caterpillars Proves Its Worth
Research
Maple Syrup Digest
Ann Hajek
Vol. 4A, No. 1
February 1992
REF# 213
A fungus that slaughters gypsy moth caterpillars proved its worth in the first large-scale field tests this
spring by destroying up to 74 percent of the targeted caterpillars.
Furthermore, the fungus successfully caused infections at 27 of the 34 experimental fungal release sites.
"Even though the fungus thrives in wet conditions, the fact that the fungus was so active in this year's
dry weather and relatively easy to introduce to new areas is very promising," said Ann E. Hajek, an insect
pathologist at the Boyce Thompson Institute for Plant research, a private, independent research
organization based at Cornell University.
Last year, in a smaller study under more normal, wetter weather conditions, up to 95 percent of the
targeted gypsy moth caterpillars were killed by the fungus.
Gypsy moths continue to be a major problem. In 1990, about 7.4 million acres were defoliated in the
Northeast, and experts predict that gypsy moths may continue to increase in 1992 and spread to new
areas.
The success of this year's experiments fortifies earlier hopes that the fungus could be used as a lethal
biological weapon against the leaf-devouring gypsy moth, perhaps by the end of the decade, said Hajek.
The fungus is harmless to animals; it attacks only gypsy moths and a few closely related caterpillars. Yet,
relocating the fungus and its habitat soil from one region to another requires detailed study to ensure
that other hidden plant pathogens are not unintentionally spread, Hajek said. Before commercial
availability, the fungus will also have to be grown in mass production.
Furthermore, Hajek and collaborator Joe Elkinton of the University of Massachusetts have found that
the fungus is spreading fairly rapidly on its own - though not as quickly as the gypsy moth - and will
devastate even relatively low-level gypsy moth caterpillar populations, unlike the commonly occurring
nucleopolyhedrosis virus (LdMNPV) which only strikes when gypsy moth populations become very
dense.
"The fungus is not a silver bullet. We do believe, however, that it may be an extremely important
mortality factor that is easy to manipulate and introduce into new sites," Hajek predicted.
When gypsy moth caterpillar populations were ravaged by a fungus in several northeastern states in
1989, Hajek and Elkinton set out to study the fungal pathogen. With colleagues at Cornell, University of
Toronto, and the U.S. Department of Agriculture, they identified it as the Japanese fungus Entomophaga
maimaiga, which had been brought into the United States in 1909 by Harvard scientists who released it
in 1910 and 1911 near Boston. E. maimaiga is known to be a deadly natural enemy of gypsy moths in
Japan, Korea and northern China but had not been noticed here until two years ago.
In 1989, Hajek and Elkinton found the fungus in almost all the samples they collected from
Massachusetts, Connecticut, New Hampshire, eastern New York, southern Vermont, northeastern
Pennsylvania and New Jersey, and in none of the samples from western Pennsylvania, Maryland or
Virginia.
By 1990, however, the fungus was found in 10 states and new areas, including central Pennsylvania,
northeastern Maryland, northern Delaware, southwestern Maine and central New York. The fungus was
still not found in West Virginia or Virginia.
In 1991, Hajek and her colleagues deposited about 7.5 pounds of soil from Massachusetts known to
have the fungus around the base of targeted trees infested with gypsy moths at 34 sites scattered
throughout northern and western Virginia, northeastern West Virginia, Maryland and western
Pennsylvania where the fungus had not been detected.
Forest rangers and research crews monitored the 34 sites as well as 15 control sites weekly during June,
looking to see if the fungus established itself and was killing caterpillars. So far, the fungus has been
found as far as 328 yards from the introduced site.
"These findings suggest that the fungus can spread on its own," said Hajek. "We now need to study how
fast it spreads."
Findings from the 1990 research have been published in the first issue of Biological Control: Theory and
Applications.
The fungus kills gypsy moth caterpillars by beginning its attack in late April or early June when eggs
hatch, Hajek said. By producing microscopic spores that invade the skin of the caterpillars, the fungus
then multiplies quickly, devouring the insect from the inside. Once infected by the fungus, the caterpillar
dies within a week or so, Hajek said, and produces spores to infect more caterpillars. The fungus also
produces another type of spore that remains dormant all winter and develops in the spring.
The fungus has kept gypsy moth caterpillar populations constant when increases and subsequent
defoliation had been expected, and in one plot caused the population to decrease. Hajek pointed out
that researchers have not yet tried to boost fungal densities to determine if there is a threshold that
would cause a gypsy moth crash.
This fall, the BTI insect pathologist and her colleagues will assess the egg-mass density on trees where
the fungus has been introduced and compare them to controls. Next year, they plan to monitor this
year's sites again to determine whether the fungus is thriving and how far it has spread. Hajek said she
also plans to study in greater detail the overwintering spore stage of the fungus.
The gypsy moth, first introduced in the United States near Boston in 1869, has spread into southern
Canada, throughout New England, New York, Pennsylvania, Michigan and more recently into Virginia,
West Virginia, Maryland, North Carolina and Ohio. In its largest outbreak in 1981, about 13.8 million
acres throughout the Northeast were defoliated - an area about the size of Connecticut, Massachusetts
and Vermont combined.
The populations then crashed to relatively low densities until 1989, when they began to climb again.
Hajek's research is supported by the U.S. Forest Service and the USDA.
The Sugar Maple Borer
Research
Maple Syrup Digest
Douglas C. Allen, Forest Entomologist, College of Environmental Science and Forestry Syracuse, New
York; and Lewis J. Staats, Extension Specialist, Uhlein-Cornell Experimental Sugar Bush, Lake Placid, New
York
Vol. 23, No. 3
October 1983
REF# 171
Few scenes distress a woodlot owner more than scarred tree trunks. This unsightly damage is of special
concern to maple syrup producers, because a sugar maple's ability to produce sap is, for the most part,
determined by tree vigor and general health. The sugar maple borer rarely kills trees, but it can be a
major cause of trunk and crown damage in sugarbushes. In some regions, incidence of borer activity is
low, but in many areas, 25 to 50 percent of the sugar maples may be attacked. Recognition of borer
damage and an understanding of the ecological conditions that favor the insect will help woodlot
owners reduce the economic impact of this pest.
The adult sugar maple borer is a black beetle distinctly marked with bright yellow bands of varying width
and shape (Fig. 1). The beetle is approximately one inch long, and it belongs to a group commonly
referred to as longhorn beetles, a name evoked by the unusually long antennae, or feeler-like
structures, that are attached to the beetles' head.
Figure 1. Sugar maple borer adult.
The beetle deposits one to a few eggs in crevices or holes that it chews through the bark, usually on the
basal 20 feet of a tree trunk. Many trees are probably used for egg laying, but the more vigorous ones
are able to overcome the newly hatched larvae. Following egg hatch, the white, grub-like larva (Fig. 2)
enters the tree and feeds beneath the bark. Eventually it excavates a shallow transverse or oblique
feeding gallery in the sapwood and inner bark (Fig. 3). As a result of this girdling, which is similar in
effect to the damage caused by an axe blaze or logging scar, large branches above the feeding site may
be killed.
Figure 2. Larva of sugar maple borer in the overwintering cell.
Figure 3. Damage caused by larval feeding. Arrow indicates transverse feeding gallery.
This is important to sugarbush operators, because the amount of sap produced by a tree is primarily a
function of crown size. Larval feeding also destroys inner bark tissues in a large area adjacent to the site
where feeding actually takes place. A large cat-faced scar or area of exposed wood is often produced
(Fig. 3) and a significant portion of the tree trunk may be rendered unusable for tapping. Sugar maple
borer scars are not always easy to detect. Sometimes they are conspicuous, but often the damage is
hidden beneath slightly cracked and loosened bark (Fig. 4). The presence of the larval gallery engraved
on the surface of the exposed sapwood (Fig. 3) distinguishes scars caused by sugar maple borer feeding
from scars that are caused by other agents, such as fungi.
Figure 4. Appearance of loosened and cracked bark that often conceals borer damage (arrows).
The borer requires two years to complete development from egg to adult. In preparation for
overwintering during the second year, the fully grown larva excavates an oval, 3/8 5/8 inch diameter
gallery that penetrates the sapwood to a depth of 2-4 inches (Fig. 2). This may severely degrade the first
board that is sawn from that part of the log. In addition to this physical damage, borer attack stimulates
a physiological response in sugar maple that protects the tree, but may further reduce the quality of
lumber cut from previously infested sawlogs. For example, chemical barriers and callus tissue develop in
the vicinity of borer injury. This is the tree's way of compartmentalizing the damage to prevent invasion
of healthy tissue by wood-inhabiting microorganisms. The callus imparts a twisted grain to newly
formed wood adjacent to the wound, while the chemical barrier results in a mineral stain, giving an
undesirable color to lumber cut from the injured portion of the log.
Recently completed research at the State University of New York, College of Environmental Science and
Forestry, showed that successful sugar maple borer attacks are generally limited to sugar maples that
have been stressed and are in a weakened state. For the maple syrup producer, a program of proper
sugarbush management that encourages maximum sap production, rapid growth and vigorous trees will
help to reduce the incidence of damage. For example, proper thinning of stands during the highly
susceptible pole timber stage, when tree diameters are between 5 to 11 inches, is especially important
in a program of preventative maintenance. If sawtimber is the management objective, removal of
previously damaged trees is also recommended to improve the quality of the residual stand and alot
growing space to sound, and presumably, more valuable trees.
The sugar bush operator should use careful judgment, however, before condemning a tree. It is not
necessary to remove sugar maples at the first sight of damage. As long as a tree pays its' way in terms of
sap production it should be preserved.
So you think they have gone away - Pear Thrips, The Little One That Causes Big Problems
Extension
Maple Syrup Digest
Bruce L. Parker, Margaret Skinner & Michael Brownbridge, Entomology Research Laboratory, University
of Vermont, Burlington, Vermont
Vol. 5A, No. 3
October 1993
REF# 222
Aerial survey results of forested lands in The State of Vermont have been completed by personnel of the
Vermont Department of Forests and Parks. Brent Teillon, Chief of Forest Protection reports moderate to
heavy damage of sugar maple trees occurred on 75,000 acres. Light damage was observed, but not
recorded, on many more. In many sugarbushes defoliation was similar to what we observed in 1988.
This year's damage was predicted in early January, based on the number of overwintering thrips found
in soil samples taken from 110 sugarbushes throughout the state. There is little doubt that pear thrips
are still prevalent in our forests and that sugar maple trees are at risk.
Many of the trees with moderate defoliation did not refoliate and the damage caused by this tiny insect
was still very evident. In July, at Maplerama, Lynn Reynolds, our President, couldn't believe the
condition of some of the trees he saw in Vermont. He said, "I had no idea pear thrips could cause such
serious damage". Although the immediate impact of thrips damage is not well defined sugarmakers
were encouraged to get out into their stands and evaluate their trees. If sugar maples were found with
significant damage managers were urged to consider reducing the number of taps used in 1994.
Vermont scientists continue to take a leadership role in developing management strategies for pear
thrips. The insect killing fungus discovered in late 1989 has now been fully tested in the laboratory. It
has great potential for practical use and recently it was formulated and tested in several sugarbushes in
central Vermont. Although results are incomplete at this time, it looks promising. On recommendations
from sugarmakers we are
taking a proactive approach and investigating the effect of these fungi on nontarget organisms. Details
of these experiments will be reported in subsequent editions of the Maple Syrup Digest.
By the time this article reaches publication The 1993 International Conference on Thysanoptera, dealing
in part with pear thrips, will be history. Vermont sugarmakers were instrumental in making it all happen.
In attendance were over 200 participants from all over the world. Experts in thrips management came
from 30 states in the U.S. and 27 different countries. Scientists, managers and growers came from as far
as S. Africa, Australia, Taiwan, Philippines, Israel, Japan, Brazil, and many of the countries in Europe. It
all helps to get a better understanding of how to manage these unique tiny insects that can cause such
severe damage to sugar maples, as we have witnessed again in 1993.
Refinement Of The Use Of Visual Traps To Predict Potential Damage To Sugar Maple From The Pear
Thrips
Research
Maple Syrup Digest
William M. Coli and Craig S. Hollingsworth, University of Massachusetts
Vol. 5A, No. 1
February 1993
REF# 218
As all maple producers know, the pear thrips has caused significant damage to sugar maple in the recent
past. Although the pest has apparently not been much of a problem in the last three years, there is
always a possibility that thrips will emerge at just the right time and in sufficient numbers to cause the
type of defoliation seen throughout the northeast in 1988.
A number of different techniques have been previously studied to monitor activity periods and numbers
of pear thrips, including soil samples, emergence traps, pan traps, and direct observation of buds and
foliage. In 1989, with the cooperation of Dr. Chris Maier of the Connecticut Agricultural Experiment
Station, we studied the possibility of using inexpensive sticky cards of various colors, called visual traps,
for monitoring pear thrips activity and relative abundance. A manuscript describing this earlier study has
been accepted for publication, and will appear in the November 1992 issue of the Journal of Economic
Entomology. The commercially-available yellow trap we chose, has been successfully used in a multistate survey project to document the distribution, activity, and relative abundance of pear thrips in 18
states during 1990, 1991, and 1992.
In 1990, the North American Maple Syrup Council, awarded us a grant of $5,000 to further study the use
of this visual trap, to determine if such traps could be used to predict eventual damage caused by the
pest. Our objectives were threefold: 1) To define the relationship between thrips captures on yellow
visual traps, and resultant foliar injury to sugar maples, 2) to study the daily flight patterns of pear thrips
at varying heights in the sugar maple canopy, and, 3) to better understand pear thrips perception of
visual traps as affected by distance, light conditions and time of day.
As I discussed at the 1991 annual meeting of the North American Maple Syrup Council, a very light thrips
year in 1991 made it impossible to complete all aspects of the funded study, necessitating an additional
attempt to complete the work, with no additional cost to NAMSC, in 1992.
As most growers are aware, and as documented by Knodel et al., (CAPS Northeast Regional Pear Thrips
Survey (Publication expected December, 1992), 1992 was also a relatively light year for pear thrips
activity and damage to sugar maples. In 1990, we demonstrated that thrips activity as measured by
visual traps could be correlated to maple foliage injury (Hollingsworth et al., CAPS Northeast Regional
Pear Thrips Survey). However, damage by thrips to sugar maple in both 1991 and 1992 was too low for
regression analysis to show any correlation.
We repeated our measurement of thrips activity at different heights in the maple canopy (0m, 1m, 2m,
5m, and 10m). Thrips were found at the 10 meter height on the same day they were found to have
emerged from the soil, and were active at all levels of the canopy throughout the season. Late in the
season, activity was concentrated in the upper levels. No differences in activity at different times of day
were determined, in part due to low thrips densities.
We also repeated our experiment to better understand pear thrips perception of yellow visual traps at
varying distances. In an arena, we captured thrips on traps 10 cm, 20 cm and 50 cm from the source, a
vial containing thrips surrounded by a water-filled moat. However, not all of these thrips had flown
directly to the trap from the source. Some had taken short flights, landed on the floor of the arena, and
then alighted on the nearby traps.
In summary, relatively low thrips numbers and damage, while certainly seen as a blessing by maple
growers, has made it impossible to confirm the utility of yellow visual traps to estimate eventual
damage from thrips, or to define daily periods of thrips activity, both important considerations prior to
initiating some sort of control action. However, our study indicates that pear thrips move rapidly up in
the maple canopy after emergence, another important finding relative to possible control options.
Finally, we can say that thrips can perceive visual traps from a distance of at least 10 and possibly as
much as 50 cm (4 to 20 inches). This offers a partial explanation as to why yellow visual traps in our trials
consistently captured thrips on the same day or earlier than emergence traps, which, due to chance,
may be positioned over a patch of forest floor which contains few or no thrips.
Is There Anything Else Out There
Research
Maple Syrup Digest
Michael Brownbridge and Alek Adamowicz, Entomology Research Laboratory, University of Vermont
Vol. 4A, No. 4
December 1992
REF# 217
If it isn't pink, what is it? When mummified pink pear thrips infected with Vertillium lecanii were
recovered from maple forest soils, all attention was focused on the evaluation and development of this
promising microbe for control purposes. But there were always a number of 'other mummified' or
'discolored' pear thrips to be found in the soils. Could it be that there are other insect-killing fungi out
there in the maple soils? We decided to look. Isolating and identifying further pathogens would add to
the arsenal of fungal agents for use against pear thrips and other forest pests.
Two methods of recovering new fungal material from Vermont forest soils were particularly fruitful
When monitoring pear thrips populations during the Vermont Statewide Soil Survey of 1990 and 1991,
miscellaneous infected and mummified larvae were extracted from the soils in addition to healthy and
pink V. lecanii-infected ones. These miscellaneous infected larvae were used in the study. Eighty-six
specimens were extracted from soils collected at 22 different maple forest stands throughout the State.
They were surface sterilized and held under conditions of high humidity to promote the outgrowth of
fungi from the bodies of the thrips. After 7 days the preparations were examined by microscope and
cultures of the fungi made when appropriate.
Secondly, soil samples taken from two maple stands and one oak stand were baited with wax moth
larvae. Just the same as fishing when you put an attractive morsel into the water to attract the fish, we
used the wax moths as bait for pathogenic fungi living in the soils. Over 300 larvae were used in this
experiment. Infected larvae were removed from the soils after 7 days, examined and cultures made.
Forty-one of the 86 fungus-infected thrips extracted were infected with recognized insect pathogens: 36
with V. lecanii, still the predominant species (but not turning the thrips pink in this instance) and
reaffirming its great potential for thrips management; three with a Hirsutella sp.; one with Paecilomyces
farinosus and one with P. lilacinus. Pathogens were isolated form 34 of the wax moth larvae:
Metarhizium anisopliae was recovered from all three sites, infecting 30 of the larvae; two P. farinosus
strains, one Beauveria bassiana and a Verticillium sp. were also isolated from the maple forest soils.
The biocontrol potential of all of these species has been well documented and inpathogenicity studies
done earlier this year, a selection of the isolates were tested against pear thrips larvae. The M.
anisopliae, B. bassiana and P. farinosus strains were all effective, causing 100 percent mortality within 5
days, similar to the V. lecanii strains originally tested. The Metarhizium, Beauveria and Paecilomyces
strains caused the bodies of the infected thrips to quickly disintegrate, which may explain why intact
pear thrips, infected with these agents, have rarely been extracted from soils. Spores from such larvae
would still be released into the soil and provide a source of infection for more thrips moving through the
soil profile.
Different species of fungal pathogens possess particular characteristics that might favor or limit their use
in an IMP program. We now have a broad base of pathogen types, which permits the selection of the
best candidate strains for use in field trials against pear thrips to be started in 1993. The strains we have
recovered could have additional advantageous traits. Forest soils may indeed be the natural reservoir of
such fungi and they are able to survive there in the absence of an insect host by utilizing dead organic
matter in the soil as a food source. This ability to persist in the environment makes these fungi
particularly attractive candidates for the control of thrips and other forest pests.
From Pink Pear Thrips To - Continuing Biological Control Research In Vermont
Research
Maple Syrup Digest
Michael Brownbridge, Bruce L. Parker and Margaret C. Skinner, Entomology Research Laboratory
University of Vermont
Vol. 3A, No. 4
December 1991
REF# 211
Now that the registration of carbaryl for use in sugarbushes has been withdrawn, it is more urgent than
ever that alternative pest management strategies are developed. Research at UVM has been geared to
the evaluation of an insect-killing fungus Verticillium lecanii, which was originally recovered from
infected pink-colored pear thrips for the control of this and other pest species.
The pear thrips strains appear to be quite unique. So what? Will the fungus be a viable control option?
We believe the fungus has great potential and that some of the unique characteristics it has make it
particularly suitable for use in a forest environment. Certainly our isolates appear to be considerably
more effective against thrips in lab tests than any of the related strains tested, killing 100 per cent of the
treated insects within 5 days. Recently we have shown that the fungus can also kill maple leafcutter
larvae, a pest which was particularly prevalent and damaging in 1991.
In our field work this year, we were trying to identify when infection of pear thrips occurs. We did not
detect any infection in adult or larval populations on the maple foliage. We therefore suspect that the
fungus survives in maple forest soils and infects thrips larvae which have fallen from the foliage and are
passing through the soil to overwinter. Indications are that infection occurs soon after larvae enter the
soil and the disease develops in these larvae quite rapidly.
Maintenance and growth of the fungus in the soil to provide a reservoir of infective material, and the
infection process itself, are undoubtedly affected by environmental factors such as temperature. We
know that the fungus can survive freezing for long periods which would allow it to remain viable in the
soil over the harsh winters experienced in the Northeast. In the spring, when soil temperatures are over
50 degrees F from around mid- May, renewed fungal growth and development of infective material can
take place. Furthermore, temperatures are also above this critical threshold when pear thrips are
entering the soil from around the end of May, so infection of the larvae can occur. Selection of fungi for
field testing will in part be based on their ability to grow and infect at low temperatures.
Of the biocontrol options, fungi offer the best hope for the successful control of pear thrips.
Information collected so far indicates that it may be possible to target the pathogen against pear thrips
when they enter the soil phase of their life cycle. The environmental conditions prevailing in the
northern hardwood forest ecosystem are favorable for such a control strategy.
Vermont Embarks On Significant Biological Control Research For Pear Thrips Management
Research
Maple Syrup Digest
Bruce L. Parker and Margaret Skinner, University of Vermont
Vol. 2A, No. 4
December 1990
REF# 207
With Financial backing from the North American Maple Syrup Council and the USDA, Agricultural
Research Service scientists at the Entomology Research Laboratory, University of Vermont are now able
to investigate the use of soil fungi for management of pear thrips. Several years ago they discovered a
significant portion of the soil inhabiting stage of this pest was infected with a soil pathogen. This
pathogen was later identified as Verticillium lecanii, a fungus which has been used in Europe for control
of other pests.
The strain of Verticillium found in Vermont, which infects only insects and close relatives, may prove to
be quite different than the one used in Europe. Hopefully it will be better adapted for use in sugar maple
stands here in the U.S.
Recently a conference was held in Burlington to discuss pest problems in sugar maple stands. The
consensus of the group of 80 scientists was that biological control of pear thrips was an extremely
promising approach. Vermont has taken the lead in this exciting new research with close coordination
with scientists in other states. Pear thrips will be studied from different parts of the entire maple
production area in hopes of finding different fungal natural enemies. The initial stages of this program
are expected to be completed in one to two years.
Biological control is an effective means of managing many of our agricultural pests. In sugar maple
stands there are few control techniques available. Sugarmakers need to insure that their final product is
pure and this biological strategy will meet that criteria and also has minimal impact on our forest
environment. Couple this with its long lasting effects and the future health of our maples will be nearly
guaranteed.
A Soil Fungus For Control Of Pear Thrips
Research
Maple Syrup Digest
Jeannie Yuill and Bruce L. Parker, Entomology Research Laboratory, University of Vermont
Vol. 2A, No. 3
October 1990
REF# 206
A fungus which infects pear thrips larvae was discovered by entomologists at the University of Vermont
while sampling for populations of the insect in the soil. This fungus occurs throughout Vermont, and its
potential for controlling pear thrips will be determined.
The nature of the fungus as a lethal agent to insects has been long known, and was first recorded in
1961 attacking a scale insect in India. Since then it has been found to cause infection in many insects
including white flies, aphids, beetles and other thrips species. The range of the fungus is worldwide,
from the tropics to the tundra.
The fungus is believed to infect pear thrips larvae in the soil, at a time when its specific growth
requirements are favorable. These include temperatures between 20-25°C and relative humidity close to
100 3/4. Once the fungus is actively growing it can penetrate the insects body and multiply rapidly
inside, causing death in as little as 24 hours. Symptoms of infected pear thrips larvae include
mummification and a pink discoloration.
As a result of the overwhelming defoliation of sugar maple by pear thrips in 1988, entomologists at the
University of Vermont started to monitor thrips populations throughout the state. During this process it
was found that in certain 14 sugarbushes, high percentages of pear thrips larvae were pink instead of
their normal white color. These larvae were cultured on agar, and the disease causing agent was
identified as Verticillium lecanii. From the 1988 season the percentages of pink larvae from the
Northern, Central and Southern sections of the state were often 12 percent.
A follow-up study was conducted in 1989 in which symptomatic pear thrips larvae throughout Vermont
were cultured and identified. It was found that of all diseased larvae cultured 80 percent were infected
with V. lecanii. Also, as in 1988, the highest density of diseased larvae was in the southern section of
Vermont.
The fungus is cultured and formulated in England and the Netherlands as a biological agent against
glasshouse pests such as white flies and aphids. In the moist, humid glasshouse environment it is an
effective control agent. Its potential for use in a forest environment is presently being investigated at
the University of Vermont. Researchers feet optimistic that under favorable conditions this fungus will
be a useful control for pear thrips.
Pearthrips - A Threat To North Eastern Sugar Maple
Extension
Maple Syrup Digest
Gary E. Laudermlich, Commonwealth of Pennsylvania, Department of Environmental Resources, Office
of Resources Management, Burearu of Forestry, Division of Forest Pest Management, Northern Area,
Wellsboro, Pennsylvania
Vol. 28, No. 4
December 1988
REF# 195
Sugar Maple foliage throughout much of northeastern United States was damaged this spring by a very
small insect known as pear thrips, Taeniothrips inconsequens (Uzel). To residents of northern
Pennsylvania, this damage is common and has been occurring for nearly a decade. Other more northerly
states are experiencing their first encounter with thrips damage.
Foliage damage by thrips resembles late frost injury. Light to moderately damaged leaves are 30-50
percent smaller than normal which makes the tree crown appear thin. The individual leaves have a
puckered appearance and are mottled yellow to pale green. Heavily damaged leaves are reduced in size
by nearly 70 percent and will be more severely puckered and mottled. The leaf margins have a tattered
or torn appearance. The tree crown has a brownish cast to it and is noticeably thin.
What effect is this insect having on sugar maples and what implications does it have for syrup
producers? Very little research has been conducted to measure the impact of the thrips on the health of
infested sugar maples. However, based on what we know about a tree's food production system, we can
make some assumptions.
A tree needs foliage to produce the food it needs for both the current season's growth and some to
store in the root system to fuel foliation the following spring. It is probably safe to assume that thrips
damaged foliage, which is sub-normal in both quality and quantity, will alter the food production
capability of a tree. Also that repeated attacks over a number of years will result in lower overall vigor of
the tree. Compound this with other stresses such as deficient rainfall (as in 1988), frost damage, and
defoliation by other insects, and the prognosis in not good.
Unfortunately, there are no practical controls for this insect, chemical or otherwise. Until suitable
controls for this insect become available, forest managers must attempt to control the other factors that
influence a tree's vigor. For example, tapping, cultural practices, and damage by insects are stresses that
often can be modified. Some suggestions for stressed stands are:
•
Monitor trees periodically for damaging agents or signs of stress.
•
Identify those trees with such signs of stress as branch dieback, defoliation, reduced sap
production or sugar content.
•
Limit tapping on stressed individuals.
•
Forego thinning operations or operating heavy equipment in affected stands. The initial effect of
thinnings and root compaction are stressful to residual trees.
•
Intervene when insects such as fall cankerworm or forest tent caterpillar pose a further threat to
tree vigor.
Work is underway to look for answers to the multitude of questions we have about thrips Several states
and the U.S. Forest Service have formed the "Regional Pear Thrips Committee." The objectives of this
consortium are:
1.
To gather and disseminate pertinent information about pear thrips impact, surveys, control,
biology, and research action on sugar maple.
2.
To coordinate training, survey methods, management recommendations, and research activities
on sugar maple.
3.
To identify needed research and training.
In addition, research is being initiated by the States of Vermont, Pennsylvania, and Massachusetts and
the U.S. Forest Service to investigate ways to survey for pear thrips and methods to control the effect of
pear thrips Investigation into the biology and control of pear thrips will not yield results quickly. There is
only one generation of thrips in a year. This species gives us only a fleeting glimpse of the adults, the
larvae are quite small and furtive, and for about nine months of the year, they are completely secretive
because they are in the ground. None of these habits are conducive to easy observation.
Until we have answers to the pear thrips mysteries, forest managers and sugar bush operators are
advised to do what they can to limit other stresses on these trees. Perhaps it will be possible to have our
maples and eat them too.
Sugar Maple And Pear Thrips
Extension
Maple Syrup Digest
Carl E. Palm, Extension Assistant, SUNY: College of Environmental Science and
Forestry, Syracuse
Vol, 28, No. 3
October 1988
REF# 194
Tiny black insects, commonly called thrips, could be responsible for the abnormal appearance (leaf
tatter) of sugar maple foliage in many areas across New York State. Recently, foresters in Pennsylvania
associated the pear thrips (Taentothrips Inconsequens (Uzel)) with sugar maple leaf distortion and
defoliation (Simons, 1985).
Figure 1. Enlarged adult pear thrips.
The pear thrips, a native of Europe, was introduced as early as 1904 to California and later was found on
the East Coast (Stannard, 1968). The pear hrips is economically important to growers of plums, cherry,
apple and pear on the West and East Coasts Borror, et al., 1979). Additional hosts of the pear thrips are
maple, basswood, birch, beech, ash, and black cherry (Simons, 1985). In Europe, this insect is associated
with woodland vegetation (Lewis, 1973).
Life Cycle And Description
The adult pear thrips has a slender brownish body and is 1.2-1.5 mm long with a yellow to orange
subintegumental segment. Its head is swollen behind the eyes and has red pigmented ocelli. Antennal
segments V and VI are broadly jointed, the third segment is yellowish brown. Tarsi are yellowish-brown
and the fore tarsi have an apical tooth adapted for digging. Wings are long, narrow, and fringed with
long hairs. The fore wings are brown and the hind wings are pale.
Only female pear thrips are known to occur in North America. Therefore, the thrips probably reproduce
asexually (parthenogenisis). Both sexes are found in Europe (Stannard, 1968). Eggs are laid mainly in the
petioles of blossoms and leaves as soon as buds open., Egg laying is performed with a sharply pointed
down- curving, saw-toothed ovipositor, Small brown scars develop soon after eggs are laid.
Young pear thrips are small and white with red eyes. Because the larvae feed on the foliage, they may
add to the injury caused by adults. After two or three weeks of feeding, the larvae fall to the ground,
enter the soil to depths of up to 40 cm (Cameron etal., 1916), and form pupal cells. Strong spines on the
9th and 10th abdominal segments are used to penetrate the soil and mold a pupal cell. In the fall, the
insects pupate within the cells and remain in the soil until the following spring. Adult pear thrips emerge
in spring when soil temperature has risen to between 7 or 12 degrees Celsius ( = 45 to 50 degrees F)
(Lewis, 1973). After emergence, adults migrate to the expanding buds and begin to feed. There is
apparently one generation per year, adults appearing in late April to early May, and larval feeding
finished by early June.
Injury
Foliar damage is caused when thrips scrape and rasp tender plant tissue with their sharp, needle-like
mouthparts to feed on plant liquids. Leaves damaged by the pear thrips are dwarfed, mottled yellow to
green-brown, and distorted. This causes the tree to have a thin crown, and the effect resembles late
frost damage. Blister-like scars develop along the veins and petioles of the foliage. Moderately damaged
foliage can place the trees under some stress and possibly cause premature leaf drop in early fall.
Severely damaged foliage could result in early spring defoliation followed by refoliation in June or July.
Management
Pear thrips have many natural enemies in North America (Lewis, 1973). The importance of these natural
enemies is not known.
No insecticides can be recommended at this time to control pear thrips.
Pear Thrips Damage To Vermont Sugar Maples 1988
Extension
Maple Syrup Digest
Vol. 28, No. 3
October 1988
REF# 193
What Is the Extent of Damage?
Pear thrips has damaged sugar maple throughout Vermont and other northeastern states in 1988.
Damage severe enough to be mapped from the air occurred on 466,000 acres. This is over one-sixth of
the maple forestland in the state. In 1987, 22,000 acres of thrips defoliation were mapped.
The most widespread damage is in southern Vermont. One-half of the maple forestland in Bennington
County and one-fourth of the maple forestland in Windham County has serious damage.
The acreage defoliated by pear thrips in 1988 exceeds the worst year of defoliation by forest tent
caterpillar (332,000 acres in 1982) which resulted in over 33,000 acres of mortality.
Damage is most severe in sugarbushes and other forestland where sugar maples predominate.
What Will Happen To The Trees?
Most pear thrips have returned to the soil, and will remain there until next spring. There will be no more
defoliation from thrips in 1988.
Pear thrips defoliation hurts trees because
•
the loss of leaves reduces their ability to manufacture food
•
serious damage kills next year's (1989) buds, which will lead to twig dieback
•
more sunlight hits the forest floor, increasing drought stress
Defoliated trees are beginning to produce a new crop of leaves (refoliate). These trees will be able to
take advantage of the remainder of the growing season to manufacture food. The trees' ability to
refoliate and replenish their food reserves will be seriously reduced if dry conditions continue.
What is Being Done?
Needed research is underway to provide answers and make recommendations for next year. Research
planned or in progress includes:
•
positive identification of the causal agents, by thrips experts
•
a soil sampling system to assess thrips distribution and density
•
experimental insecticide and fertilizer applications
•
preparation of a technical report summarizing all existing knowledge of the insect
•
remote sensing of damage regionwide using photography and/or satellite imagery
What Should Landowners Do?
Forest landowners and sugarmakers should inspect their maple woodlands now to find out whether
their trees have been defoliated and whether or not trees are refoliating Refoliating leaves are still small
and red or yellow in color.
Trees which have been defoliated should be disturbed as little as possible. Sugarbushes should be
tapped conservatively. If trees have been severely stressed, it would be best not to tap at all the
following season. Thinnings should be postponed for three to five years after the last year of defoliation.
For More Information Contact
Vermont Department of Forests, Parks and Recreation Brent Teillon, Chief of Forest Resource Protection
244-8711
University of Vermont Dr. Bruce Parker, Entomologist 658-4453
Can Pear Thrips Fungal Pathogens Be Used Against Other Maple Pests
Research
Maple Syrup Digest
Leticia Martinez de Murguia, Michael Brownbridge & Bruce L. Parker, Entomology Research Laboratory,
University of Vermont
Vol. 4A, No. 2
June 1992
REF# 215
An intriguing question. Research is continuing at the Entomology Lab on the evaluation of the insectkilling fungus Verticillium lecanii, and other entomogenous fungi, for the control of pear thrips. Our
findings so far indicate that these pathogens, which are indigenous to maple forest soils, are very
effective against thrips. But no forest pest can be considered in isolation and a large and diverse group
of insects feeds on sugar maple. It is important that the interactions of the different populations be
recognized and that control strategies should be formulated to take a more holistic approach to pest
management. We have therefore undertaken a complementary research project, funded in part by the
NAMSC, to investigate the effects of selected fungal pathogens on the maple leafcutter, Paraclemensia
acerifoliella.
This pest first appears in May, when the small, shiny, metallic blue moths can be seen flying around in
the sugarbushes. Feeding on maple leaves starts in early June and continues through summer until
September when the larvae drop to the ground to pupate. Few people may have observed the naked
larvae, rather they will have noticed circular holes in the maple leaves which get progressively larger as
the season progresses. The insect cuts leaf discs to form a protective casing around itself, hence the
circular holes, and then feeds on other parts of the leaf. Leaf cutting and feeding damage by the insect
on maple foliage in 1991 was extensive and spectacular, and leads to a reduction in tree vigor and sugar
content in sap.
The entomogenous fungi tested against this pest are all pathogenic to thrips. To evaluate them against
the leafcutter, maple leaves were coated with suspensions of the fungus, and larvae, complete with leaf
casing, allowed to crawl over the treated surface. For some of the strains tested, 90% to 100% of the
exposed larvae had died after 8 days, showing that they were very susceptible to these biological control
agents. Larvae infected with V. lecanii also became pink, the symptomatic color of pear thrips infected
with the same organism.
Further studies are now underway to see how well the V. lecanii strains perform against maple
leafcutter at temperatures equivalent to those experienced in a sugarbush environment. The results are
exciting, suggesting that this pest might also be managed with fungal pathogens being developed for
pear thrips control. This way, one pathogen could potentially be used against several pest species in the
same sugarbush environment.
Recent Developments In The Biological Control Of Pear Thrips
Research
Maple Syrup Digest
Michael Brownbridge and Jeannie Yuill, Entomology Research Laboratory University of Vermont
Vol. 3A, No. 2
June 1991
REF# 208
Pear thrips larvae infected with the fungus Verticillium lecanii were initially recovered from sugarbush
soils sampled in VT during 1988 and 1989. With the undertaking of a Regional soil survey in 1990 to
determine the distribution of pear thrips throughout maple producing areas in the north east, the
incidence of pink infected larvae was shown to be much wider. Larvae infected with this fungus were
found in soil samples taken at sugarbush sites in CT, MA, NH and PA. This widespread natural occurrence
provides further incentive to fully evaluate the biocontrol potential of this fungus, and how transmission
of the disease in the environment may. be promoted.
To date, over 50 isolates are held in the Entomology Lab at UVM and have been maintained in various
ways to ensure full retention of their viability and potency. A series of experiments are underway to
enable us to select the best isolates for possible use in the field, according to certain criteria. These
include: 1. selection of the most toxic strains as those having the best chances of infecting and killing
pear thrips; and 2. selection of "cold- hardy" strains capable of infecting thrips in the cool sugarbush
soils and surviving there over the winter months.
In preliminary lab experiments, we have managed to artificially infect pear thrips larvae with a number
of the fungal isolates, the dead larvae developing the characteristic pink coloration observed in diseased
specimens collected from the field. The pear thrips isolates also seem to be quite unique in their
production of this pink pigment, which has not been evident in cultures of strains of the same species
isolated from other insect hosts.
Much remains to be done, but we feel we are taking the first steps along the road to the development of
an efficient, cost effective and environmentally sound alternative for the management of pear thrips.
Figure 1. Fungus Infected Pear Thrips Larva.
Should We Forget Pear Thrips - An Update From Vermont
Research
Maple Syrup Digest
Bruce L. Parker and Margaret Skinner, Entomology Research Laboratory, University of Vermont; H.
Brenton Teillon, Department of Forests, Parks and Recreation, State of Vermont
Vol. 3A No. 3
October 1991
REF# 209
Should we forget pear thrips? Will sugar maple trees in 1992 yield butterscotch? Of course not is the
definitive answer to both of these ridiculous questions.
Research continues at UVM to develop management strategies for this troublesome tiny thrips pest that
has plagued sugarmakers for over a decade now. Efforts in Vermont were started in late 1988 in
response to public demand because of the defoliation of 500,000 acres of sugar maples.
Sugar maples this year in Vermont appear healthier than they have in quite a few years. It is good to see
but don't be lulled into a false sense of security, for pear thrips, as well as other pests, are still alive and
well. Keep in mind that this insect doesn't have to create damage to be successful in its efforts for
survival and reproduction. The healthy trees could and probably did produce healthy pear thrips.
Preliminary results from soil surveys in several research sites in central Vermont show that significant
populations are there now and will be there for the winter.
One of the major thrusts of our research centers around the use of a naturally occurring fungus for
controlling thrips. This fungus was discovered in thrips populations in 1989 and since then we have been
able to demonstrate its ability to kill pear thrips. Equally as exciting is that this fungus shows potential
for killing other sugar maple pests like the maple leafcutter. This pest, a late-season defoliator, caused
severe damage this year in many areas.
This past summer we conducted a number of experiments to determine when pear thrips are actually
infected with this fungus. It appears as though most of the infection occurs after the pear thrips larvae
fall from the trees and enter the soil for the winter. This is important to know because we plan
eventually to apply the material to a sugarbush in a pilot test and proper timing is essential. This
research was in part supported by NAMSC.
Aerial surveys done by the State of Vermont protection personnel to determine the extent of pest
damage to sugar maples are now complete. These reports support our premise that our sugar maples
are looking good although light defoliation was detected from the ground. Next year may be different
and our research plans are geared to being prepared for just that potential. So enjoy the green for who
knows what tomorrow will bring!
Figure 1. Taeniothrips inconsequens (Uzel)
Maple Leafcutter - The Ingenious Defoliator
Extension
Maple Syrup Digest
Douglas C. Allen, State University College of Environmental Science and Forestry Syracuse, New York and
Lewis J. Staats, Uihlein Sugar Maple Research Extension Field Station Lake Placid, New York
Vol. 25, No. 2
July 1985
REF# 180
In recent years, you may have noticed sugar maple foliage turn light brown during mid-to late summer.
The discolored leaves usually contain holes that vary in diameter from one-eight inch to about the size
of a nickel (Figure 1, A). At first glance, the insect responsible for this damage is not readily apparent.
Inspection of these leaves may reveal pancake-shaped pieces of leaf tissue that are attached to the
surface of the leaf (Figure 1, B). Without a closer look, however, the responsible party remains elusive.
These signs of defoliation are increasingly prevalent throughout northern hardwood stands in New
England, New York and parts of southeastern Canada. The culprit is a clever and potentially noxious
moth called the maple leafcutter, known to forest entomologists as Paraclemensia acerifoliella. High
leafcutter populations can significantly reduce the quantity and quality of sap produced by affected
sugarbushes.
Figure 1. Close-up of maple leafcutter damage (a) and shelter made from leaf discs (b).
Causes of Foliage Discoloration
Changes in the appearance of sugar maple foliage results from a combination of three types of damage;
leafmining, skeletonization of foliage and holes in the leaves. Brown blotches are first evident on the
leaves in late June shortly after the caterpillars hatch from eggs. The young caterpillars enter the leaves
and live, fully concealed, between the upper and lower surfaces of the leaf. Wherever these leafmining
stages feed, only the light brown and semitransparent outside surfaces of the leaf (i.e., upper and lower
epidermis) remain intact (Figure 2). Completed mines are one-half to three-quarters of an inch long. The
leafcutter abandons the leafmining habit after two or three weeks, and begins skeletonizing the leaf
surface. At this time the caterpillar consumes the green tissue, but not the leaf veins, in a circle as far as
it can reach around the perimeter of its' case. When all the reachable tissues are eaten, it moves to
another location on the same or an adjacent leaf. It can not feed directly beneath the case, therefore,
feeding results in many disk-shaped patches of green ringed by skeletonized tissue (Figure 3a). The latter
gives the damaged area a lace-like design. It is during this transition from leafminer to skeletonizer,
usually in early July, that caterpillars are most vulnerable to insecticides. Finally, holes in the leaf result
when each caterpillar constructs it's oval case. The case, or shelter (Figure 1b) is made from two discs of
leaf tissue that the insect removes from the leaf and lashes together with silk. Silk is also used to attach
the case to a substrate, usually a leaf. The caterpillar feeds beyond the perimeter of the lower, smaller
disc (Figure 3b), but is rarely visible because the larger upper disc serves as a roof that covers its' entire
body (Figure 3c). The case is portable and whenever the insect moves to a new feeding site, so does its'
shelter!
Figure 2. Example of feeding damage caused by a leafminer.
Figure 3. Maple leafcutter feeding results in patches of skeletonized leaf tissue (a). Note the top (b) and
bottom (c) of the case, which has been turned over to expose the leafcutter caterpillar (white arrow).
Presumably, this ingenious case-making behavior protects caterpillars from adverse weather and many
natural enemies. The case is enlarged by cutting successively larger discs each time the insect molts.
Molting is a process by which the caterpillar sheds its' old skin and creates a new one. This
phenomenon, inherent to all insects, is necessary for the caterpillar to grow and progress to the next
larval stage.
Life History
Moths deposit eggs from mid-May to early June, but because the adults are very small, they are rarely
observed unless populations are very high. During outbreaks, however, the small, steel blue moths with
yellowish-- orange heads are readily seen on the undersides of leaves. The combination of discolored
foliage, holes that result from disc removal and the presence of oval cases attached to leaves, branches
or tree trunks, are the most readily detectable signs of the insect (Figure 4). Caterpillars emerge around
mid-June from eggs that are deposited in small pockets pierced by the female moth on the underside of
sugar maple leaves. When larvae complete feeding in late August or early September, they drop to the
ground or descend trees with their cases in preparation for overwintering as pupae among the fallen
leaves. At this time of year, sugarbush owners are often presented with a rather bizarre sight as
hundreds of brown pieces of leaves "walk" down tree stems and across the ground!
Figure 4. Typical appearance of a sugar maple leaf Infested by maple leafcutter.
Consequences of Defoliation
Early in an outbreak, extensive feeding damage is usually confined to regeneration or mid- and lower
crown foliage of overstory trees. Defoliation usually becomes evident in late June or the first week of
July, but unless populations are very high, damage may not be obvious until late August. The earlier that
heavy defoliation occurs during the summer, the less opportunity the tree has to produce adequate
food needed for current growth and for reserves that will be required the next growing season.
Consequently, in sugarbushes that are heavily defoliated, production of sap with lower than normal
sugar content is likely the following spring.
In a recent outbreak of maple leafcutter in Vermont during the 1970's, a few pole to small sawtimersized stands experienced extensive crown dieback after only one year of heavy leafcutter defoliation.
Mortality averaged 10% of trees six inches in diameter and larger. Forty-three percent of the remaining
trees were in poor condition. In general, however, throughout the 42,000 infested acres, significant tree
stress did not occur until trees were subjected to three years of heavy browning. Degree of stress was
determined from annual samples of root starch. Low starch levels indicate low tree vigor and represent
the end product of severe stress. After one or two years of heavy "browning", sugarbush owners should
assess the condition of their trees and, if appropriate, consider control measures. State or Provincial
forestry agencies should be consulted before making a pest management decision, however. These
professionals may assist you with the evaluation and will bring you up-to-date on control
recommendations.
Acknowledgments
We thank Mr. H. Brent Teillon and Mr. Ronald S. Kelley, Department of Forests, Parks and Recreation,
Montpelier and Morrisville, Vermont, respectively, for providing editorial comments and unpublished
observations about maple leafcutter.
Fall Cankerworm Defoliation Warrants A Watchful Eye
Extension
Maple Syrup Digest
Douglas C. Allen, State University College of Environmental Science and Forestry Syracuse, New York
and Lewis J. Staats, Uhlein-Cornell Experimental Sugarbush Lake Placid, New York
Vol. 27, No. 2
July 1987
REF# 188
Outbreaks of this defoliator, known to science as Alsophila pometaria Harris, have been reported
periodically in the northeastern United States since 1790, but mention of infestations appeared in
colonial literature as early as 1661. These early writings make fall cankerworm one of the oldest insect
pests recorded in North America. It belongs to the moth family Geometridae (from the Greek geometr
meaning land-measurer). Members of this group are commonly referred to as spanworms, measuring
worms, inchworms or loopers These terms reflect the caterpillar's peculiar method of locomotion.
Because it is not equipped with legs in the middle of its body, the caterpillar (Fig. 1) walks by bringing
the posterior end forward in the vicinity of the front legs and, in doing so, the body forms a loop. This
behavior also gives the impression that the insect is inching along. Origin of the name cankerworm, on
the other hand, is less obvious. One definition that Webster gives for the term canker is rust or tarnish.
When high populations of fall cankerworm develop, caterpillars eventually eat the entire leaf except for
the midrib and larger veins. At low population densities, however, only parts of the leaf are consumed
and uneaten portions frequently turn brown, because major leaf veins are severed when caterpillars
chew holes in the leaf blade. This discolored foliage is probably the origin of the latter part of the
insect's common name. The term fall refers to the time of year that moths are present and, in a
nomenclatural way, distinguishes this species from a close relative known as the spring cankerworm, the
adults of which are active in the Spring.
Figure 1. Fall cankerworm caterpillar (larva). This example is dark green, many cankerworms are much
lighter. Actual length is approximately one inch.
Biology - Saga of a Cold Hardy Creature
Fall cankerworms overwinter in the egg stage, which is attached to the bark of twigs (Fig. 2) or the tree
bole. The small, brown, barrel-like eggs are deposited in groups of a few to several hundred during
November and early December. Eggs hatch and the caterpillars begin to feed in late April or early May,
at about the time that host buds begin to open. When fully grown, cankerworms are approximately one
inch long, and may be pale green, reddish gray or nearly black with a pair of white to pale yellow
longitudinal lines on the back. Feeding is usually completed by early to mid-June, at which time
caterpillars crawl down the tree and enter the soil to pupate. The pupa is a quiescent stage during which
the caterpillar eventually transforms into a moth. The cycle is completed in late Fall when moths
emerge, mate and oviposit.
Figure 2. Fall cankerworm egg mass. Actual length of mass is one-quarter of an inch.
The female moth is wingless (Fig. 3) and must crawl to the nearest tree and then ascend into the crown
to deposit eggs. While patiently waiting on a deer stand in late November, we have often watched the
glossy, light to dark ash-gray females struggle up the bole of a beech or sugar maple, and marveled at
their ability to motivate while temperatures hovered around the freezing mark. At this time of year,
flying insects are relatively rare so the brownish-gray male moths readily attract attention as they flutter
around trees in search of females.
Figure 3. Female fall cankerworm moth: A, top view, B, side view. Actual length is approximately onequarter of an inch.
Food Plants - a Broad Diet Enhances Survival
During colonial times, fall cankerworm was looked upon as a pest because the caterpillars damaged
apple trees. Indeed, apple is one of its favorite hosts. Over the centuries, however, it has earned a
reputation by defoliating a variety of tree species, especially elm, red oak, basswood and sugar maple.
Cankerworms feed at the same time, and often on the same plants, as gypsy moth. When high
populations of the two overlap, trees are stripped very quickly. Heavy defoliation (i.e., 50-60 percent or
more) early in the growing season often stimulates a tree to refoliate. The production of a second
compliment of foliage during a single growing season places trees under severe physiological stress.
Subsequently, these low vigor trees are often invaded by secondary agents such as fungi and
woodboring insects. These organisms apply the coup de grace to low vigor trees. They are secondary
only in an ecological sense, because they require a weakened or stressed tree for successful
development. Oak and elm are especially susceptible to this sequence of events. Defoliated oaks, for
example, are frequently invaded by a lethal root inhabiting fungus called Armillaria root rot and a beetle
known as the two-lined chestnut borer. The latter feeds beneath bark on the tree trunk and large
branches, and, in the process, essentially girdles the tree. Similarly, defoliated elm is attractive to the
notorious European elm bark beetle. This inner bark borer is a double threat, because it not only girdles
the tree, but beetles often inoculate the tree with spores of the Dutch elm disease fungus.
Importance to Sugarbush Operators
Early defoliation and subsequent stress to sugar maple may significantly lower sap production the
following spring. Three or more successive years of heavy cankerworm defoliation may also pave the
way for Armillaria root rot, sugar maple borer or crown dieback. These events, and others, either singly
or in combination, can have a negative economic effect on a maple products business.
Cankerworm populations are fickle, which makes it difficult to predict defoliation. Characteristically, a
two to four year outbreak is followed by several years when the insect is very scarce. Many natural
enemies help to bring about the demise of an infestation, but one of the most important is a tiny wasp
that parasitizes the egg.
Forest entomologists know very little about the conditions that allow population density to increase to
damaging levels. Therefore, we do not have a biological or physical barometer that we can use to
predict a potential for defoliation. The insect's feeding behavior, however, can provide a clear signal of
threatening conditions. The habit of chewing holes in leaves, called shothole feeding (Fig. 4), as opposed
to feeding on the leaf margin, makes cankerworm. damage, like that of many other loopers, readily
detectable. The relative abundance of shothole damage from one year to the next can serve as a gross
indicator of population change or a portent of stressfull defoliation. A brief walk through the sugarbush
in late May or early June is all that is necessary to detect a potential problem. Because many geometrids
feed in this manner, a professional should be consulted before deciding whether or not control
measures are warranted.
Figure 4. Sugar maple leaf showing typical shot hole feeding damage.
Pest Management Recommendations
First of all, sugarbush operators should contact service foresters or extension specialists on a regular
basis to learn if cankerworm infestations occur in the region. These people may also be able to provide a
pest leaflet that describes the insect in more detail. As is the case with all major forest pests, it is
important for concerned people to familiarize themselves with the damage and general appearance of
potential pests. Early detection and conscientious monitoring of population change is important, and
these activities are essentially your responsibility as a forest manager or landowner.
When a suspicious condition is discovered, consult a specialist to verify identification and have your
situation evaluated. If conditions warrant, the specialist will be able to recommend currently approved
control measures.
Biological Control - A Major Component in Integrated Pest Management I. Overview and Introduction
Extension
Maple Syrup Digest
E. Alan Cameron, B.C.E. Department of Entomology Penn State University University Park, PA 16801
Vol. 9A, No. 3
October 1997
REF# 406
Integrated Pest Management, or IPM, is widely accepted today as the philosophical basis of managing
pests of commercial crops. It is endorsed officially through statements by President Clinton, and
embodied in policies advocated and promoted by the United States Department of Agriculture (USDA).
IPM attempts to minimize cost of 'controls,' of whatever kind, and to use, when necessary, only those
control tactics which are environmentally sound and economically justifiable. We want to nudge, rather
than bludgeon, the natural production system. Our overriding goal is to create an environment in which
a pest has difficulty surviving, or at a minimum an environment in which pest populations do not build
to levels which cause economic damage to the crop we are attempting to produce. IPM was proposed
initially for management of insect pests in agricultural crops; early development took place in cotton
ecosystems in California in the 1950's and 1960's. The philosophy has become the basis of more and
more insect and disease pest management programs in crops across the spectrum, from short-term
glasshouse production (where there may be multiple crops in a year) to long-term, relatively stable
systems such as those found in forests.
The production of maple syrup depends on maintenance of a healthy stand of sugar maple trees for
many decades, in spite of repeated tapping to harvest sap from the trees and in the face of the normal
hazards to which trees are exposed as they grow, mature, and age. Tapping activity physically opens a
tree to potential invasion of pathogens by providing infection courts with each drilling through the bark.
Removal of sap in excessive quantities has the potential to weaken, or stress, the tree; stressed trees
are, in general, more vulnerable to attack by both insects and diseases. Growers have learned, through
many years of experience, how to balance sap collection while at the same time minimizing or
preventing damage to their trees - the investment capital on which they depend. Problems may arise
when Mother Nature throws a curve in the form of unanticipated insect outbreaks, drought, or other
environmental perturbations. Because we are dealing with a resource (the trees) which is in place for a
long time, we must be concerned with management practices which can be maintained over - and which
are effective for - long periods of time. Such a situation is one that is favorable for development and
implementation of an IPM program. Integrated pest management has been defined as the utilization of
all available methods, in an economically sound and environmentally acceptable manner, to maintain
the population of a pest organism below its economic threshold. Implicit and explicit in this definition is
the acceptability, at carefully determined times and for clearly defined reasons, of all methods of pest
reduction. These include, for example, silvicultural manipulations of the crop (in this case the sugar
maple trees, to control age, spacing, and species composition of the forest), the use of chemical or
biological pesticides to bring about the immediate suppression of a problem that has grown to
unacceptable levels, and the use of biological organisms to reduce pest populations, maintain pest
populations at economically acceptable levels, and minimize the likelihood of future eruption of these
pests. In the final analysis, we are attempting to create a natural environment in which the organism(s)
we value, i.e., the sugar maple trees, grow and prosper. At the same time those organisms which might
damage the trees are, themselves, subjected to forces which mitigate against their survival and
development. Because we are dealing, in the management of a sugarbush, with a crop which is in place
for a long period of time, we opt, whenever possible, for management techniques which will persist over
time. Such techniques will minimize repeated expenditures for short term 'control' actions, while
simultaneously contributing to long term 'management' activity and stability.
Biological control, that is, the use of beneficial living organisms to assist in the management of
populations of pest organisms, has gained renewed popularity in recent years. By its nature, biological
control focuses on long term, sustainable management. Consequently, it is highly desirable and may
have great promise for use in a program designed for management of pests in a crop which depends on
stability over time for maximum return. Extensive legal and operational safeguards are in place to insure
that the use of biological organisms for control of a pest will be environmentally compatible, sound, and
safe, and that there is virtually no possibility that the organisms used will, themselves, become pests at
some time in the future. Even though the initial costs of establishing a biological control program may
not be particularly low, the long term return on investment is where dividends are realized. Once
established, 'classical' biological control requires minimal or perhaps or subsequent financial inputs over
the years to maintain itself. 'Augumentative' or 'inundative' approaches to biological control require
repeated, even annual, inputs. But the environmental benefit, coupled with the economic benefit,
justifies such investments in those situations where they are used.
Many insect pests of crops in the New World, and also plants which have become weeds, have been
introduced from abroad both through our own carelessness and through honest ignorance. Well-known
forest pests such as the gypsy moth and the European spruce sawfly, pests of fruit such as the codling
moth on apple, the Oriental fruit moth on a number of stone fruits, and the cottony cushion scale on
citrus, the Hessian fly in wheat, and purple loosestrife which has become a widespread weed in much of
the eastern United States, were all either brought to this country accidentally or escaped containment
once they were brought in deliberately. In each case, these pests arrived without any of the natural
enemies that help to keep their populations below the economic threshold in most years in their areas
of origin.
Let me describe the three major approaches to biological control.
Almost 110 years ago, the first - and extremely successful - attempt was made to recreate a natural
balance between a pest insect, the cottony cushion scale which was devastating citrus crops in
California, and natural enemies common in its native home in Australia. Within 18 months after the
introduction of the vedalia beetle (a 'ladybird beetle' which feeds on the scale) into California, the citrus
industry was quite literally saved from the brink of extinction. The introduction of a natural enemy,
usually from the native home of the introduced pest, has come to be known as 'classical' biological
control. The introduced beneficial species may be a parasitoid, a predator, or a pathogen.
'Augmentative' biological control involves the release of relatively large numbers of individuals of a
beneficial species. This species usually is a para sitoid or a predator; the addition of large numbers of
individuals is designed to add to the already-present population of this species in the area of the release.
It is not the introduction of a new species for purposes of establish ment. Augmentation may be
necessary because established populations of the beneficial species have been decimated as a result of
too few hosts being present for a few years, differentially adverse weather conditions or other
environmental stresses, or perhaps accidental reduction of the beneficial species as a consequence of
use of toxic insecticides.
'Inundative releases' for biological control consist of the application of large numbers of individual
parasitoids or predators to relatively a small area during a concentrated period of time. Rarely is there
an expectation that the species being added will become established and maintain naturallyreproducing populations. In a single growing season, there may be multiple releases within the same
generation of the pest, or during each generation of a multivoltine pest. The objective of an inundative
release is to kill as many of the hosts as possible, much as one would if a chemical insecticide were used;
the objective is not the establishment of the parasitoid in the environment as a continuing and
sustainable component of the natural system. In effect, inundative releases are the use of a biological
insecticide.
This is the first of a series of articles in which I will describe in some detail, and with examples of
successful programs, biological control of insect pests. Subsequent articles will elaborate on the several
kinds of biological control I have identified, that is, classical, augmentative, and inundative, and finally I
will attempt to assess possibilities of implementing one or more of these into management of pests of
sugarbushes. Intertwined with the benefits, I will also identify some of the challenges that those of us on
the research and development side of the picture must be overcome before these technologies can be
turned over to growers for routine implementation in their own operations. We must continue to work
to transform the 'art' of biological control into the 'science' of biological control. Only as we understand
the details of the biology and behavior of each of the players in the pest management puzzle will we
progress toward our goal. Working together, we will succeed, but it will not happen overnight.
Biological Control - A Major Component in Integrated Pest Management II. Classical Biological Control
Extension
Maple Syrup Digest
E. Alan Cameron, B.C.E. Department of Entomology Penn State University University Park, PA 16801
Vol. 9A, No. 3
October 1997
REF# 404
In the first article in this series, I presented an overview of the integrated approach to pest
management, commonly called IPM. I also briefly described the three major approaches to biological
control - classical biological control, augmentative releases, and inundative releases. And I noted that
biological control is one of the important elements in an IPM approach to coping with insect and disease
pests of crops. This second article will elaborate on 'classical' biological control.
In the 1880's, the citrus industry in California was threatened with destruction as a result of damage
caused by the cottony cushion scale, Icerya purchasi. Fruit production was reduced by over 95% in a
matter of just a few years. The Department of Agriculture of the State of California sent an
entomologist, Mr. Koebele, to Australia. There he was able to find both a coccinellid predator, a
'ladybird beetle' called the vedalia beetle (Rodolia cardinalis), and a parasite in the order Diptera
(Cryptochaetum iceryae), which attack the damaging scale insect. Modern transportation facilities were
not available a century ago. Through laborious efforts, Koebele maintained colonies of the scale pest on
small citrus trees in pots on the deck of the steamship on which he returned to America. On some of
these small trees, he also maintained colonies of the two natural enemies. Enough individuals of both
beneficial species survived the journey that Koebele and coworkers were able to initiate colonies in a
laboratory in California once he returned, and have adequate numbers of the beneficial insect species
available for release into California citrus groves.
Within a year, the Vedalia beetle had dramatically reduced scale infestations, especially in the major
citrus growing areas of southern California. The beetle became established in its new environment
quickly, and spread rapidly, especially in the hot, dry Mediterranean climate in inland areas. Within only
two or three years, citrus production had returned to previous levels, and the citrus industry was, quite
literally, saved. The parasitic fly became established more easily in some of the cooler and more humid
citrus production areas near the coast in southern California, and in northern California. Both species
remain today, over 100 years later, as the major factors in preventing resurgence of the cottony cushion
scale. (In the early 1960's, I spent a number of days searching for both the scale, and its predator and
parasite, in southern California so I could make shipments to colleagues in the Mediterranean area. It
was exceedingly difficult to find any individuals of either the pest or its natural enemies, so effective has
the regulation of the pest remained. That is just one indication of how efficient and effective this
particular introduction of beneficial insects has been.
This example represents the first documented example of the successful use of one species of biological
organism to control another species. The success of this program stimulated a lot of work, especially in
the United States, over the next half century, to try the same technique to reduce pest problems. A large
number of our insect problems in North America are the result of accidental introduction of a pest
species from abroad. If suitable host material is available as food, pest populations often increase
rapidly once an introduced insect gains access to a new geographic area. The normal complex of natural
enemies, which exists in lands where the pest is native, is not present to prevent explosive population
growth. The overriding goal of classical biological control is to re-establish at least the most critical
elements which put adverse pressure on the growth of the pest population, and thus reduce or
eliminate the economic damage which would otherwise be caused.
There are some important factors which we must remember in any discussion of biological control.
1.
Our goal is NOT eradication of the pest. Eradication means the elimination of every last
individual of the target species. This objective (eradication) may be justified when a newly-arrived pest is
discovered shortly after its introduction, when populations are still confined to a very small geographic
area, and usually before populations have increased to damaging levels. (Indeed, this goal is under
active consideration as an option in addressing the recently-discovered Asian longhorned beetle, which
attacks maples among other species, in the Bronx.) Because the goal of an eradication program is the
elimination of ALL of the individuals of the pest species, more rigorous control methods - such as the use
of chemical insecticides in multiple applications - are commonly used.
2.
Successful biological control programs have as an important goal the longterm maintenance of
pest populations at levels below the economic threshold. That means that we must be willing to tolerate
low numbers of the pest species to serve as a food reservoir for the beneficial species. It also means that
most of the successful species which have been used in biological control programs have effective
mechanisms for searching for, and finding, their host so they, also, can survive when host populations
are low.
3.
It is not always clear where a particular pest may have originated. An insect in its native range
may normally be kept 'under control' by a complex of natural enemies, and its biology and behavior may
not even be well-known. Once the pest insect escapes the suppressive forces of its regulating agents,
populations can grow rapidly in the new environment. It is very important to expend the time and effort
necessary to attempt to determine the native range of the pest, and then to give priority to searches in
that area of the world for potential natural enemies. Modern molecular biological techniques may be
used to determine the genetic variability of populations. In an area of introduction, the genetic diversity
will be much less than one would find where the species is native. This is a new and emerging
technology, one that has not been used widely to this time but which is being used in some important
studies and is forcing some changes in long-held beliefs about the origins of some pest populations.
4.
When introductions of biological control agents are made to a new area of the world, it is
essential that we do not simultaneously introduce natural enemies of the beneficial insect. We must
carefully exclude, for example, hyperparasitoids and pathogens which might 'control' the beneficial
species which we wish to establish! That would defeat all of our efforts. As a result of this need, material
introduced into the United States or Canada today must be reared in a secure quarantine facility for AT
LEAST one generation to insure that no unwanted organisms accompanied the beneficial species when it
was brought to a new geographic area of the world. That means, of course, that we must also be able to
rear the pest insect, or a suitable laboratory substitute (called a 'factitious host'), as well as the parasite
under artificial conditions. Often this is a very difficult additional challenge that must be overcome.
In April, 1995, during an investigation funded in substantial part by a Research Grant from the NAMSC,
David Teulon and I discovered a new species of parasitoid which attacks pear thrips in Turkey. We
reported on these studies in a poster presented at the Fall, 1995, annual meeting in Kingston, Ontario,
and in an article in the Maple Syrup Digest in early 1996. For a number of reasons, we believe that pear
thrips is native to Turkey and probably other parts of Asia Minor rather than to Europe as has been
commonly accepted until recent years. In addition to the new species of parasitoid, we recovered
smaller numbers of additional species of insects parasitizing or preying upon pear thrips. Many steps
must be taken before any of these potentially valuable natural enemies can be introduced to and
liberated in the New World. But our preliminary evidence suggests that they deserve to be investigated
in more detail. In April, 1997, I returned to Turkey to collect numbers of this new species of parasitoid,
and brought them back as the next step in a biological control effort. A brief report of this work appears
in this issue of the Maple Syrup Digest and progress reports will continue to appear as significant
developments occur.
If the parasitoids we collected turn out to be restricted to attacking pear thrips and even perhaps some
close thrips relatives, it is possible that one or more of these species might ultimately be introduced to
and released in our sugar maple forests, become established, and contribute to continuing long-term
control of this pest insect. This effort, then, would take its place in a growing list of 'classical biological
control' success stories. Programs take years to implement, and there may be setbacks along the way.
But if all goes well, and if the early promise is borne out at each critical step along the way, we may look
back in the early 21st century with satisfaction in our accomplishments. The North American Maple
Syrup Council will be justifiably proud of its support of the development of the environmentally sound
biological component of an integrated pest management program directed against the pear thrips.
Collection of Parasites for Potential Use as Biological Control Agents For Pear Thrips, Taeniothrips
inconsequens
Extension
Maple Syrup Digest
E. Alan Cameron, B.C.E. Department of Entomology Penn State University University Park, PA 16801
Vol. 9A, No. 3
October 1997
REF# 405
In 1995, with support from a NAMSC research grant, Dr. David A.J. Teulon (a former postdoctoral
student) and I spent two weeks in southwestern Turkey to investigate the possibility of collection
enemies (parasitoids and/or predators) from that part of the native range of the pear thrips (Cameron
and Teulon 1996). During the last decade, the pear thrips, Taeniothrips inconsequens (Uzel)
(Thysanoptera: Thripidae), has caused considerable damage to sugar maple stands as a result of its
serious adverse impact on the production of maple syrup throughout much of the northeastern United
States and parts of eastern Canada. The insect was introduced into the New World early in this century,
and arrived without any of its natural enemies. Thus released from important natural ly-occurring
population-regulating factors, it spread widely and from time to time reaches outbreak proportions. Our
team at Penn State has been working since 1989 to understand the insect and its effects of sugar maple
(Teulon and Cameron 1996; Teulon et al., 1993, 1997), and to develop management practices to
minimize the damage caused (Cameron et al., 1996).
During our 1995 exploration, we identified a new species of insect, a parasitoid in the Hymenoptera
genus Ceranisus, in numbers that suggested it might play an important role in regulating populations of
pear thrips. In Turkey, pear thrips was fairly easily collected from blossoms of a relatively common
native woody shrub, Arbutus andrachne. With the support of an additional NAMSC research funds grant,
I returned to Turkey in April, 1997, to collect material of this species, and of other potential beneficial
species if encountered, with the objective of bringing back enough living material to establish laboratory
colonies for further study. If our expectations are borne out, we expect eventually to provide adequate
numbers of individuals for field release in an effort to establish this new species in our sugar maple
areas. This collection phase of the investigation is the first in a long series of steps to be taken in a
classical biological control program, the goal of which is to regain control over the pest insect and to do
it in an economically acceptable, and environmentally sound and compatible manner.
During our earlier trip, we established an excellent cooperative relationship with Prof. Dr. Irfan Tunc, an
entomologist with the Faculty of Agriculture, Akdeniz University, in Antalya. Once again, he and his
colleagues were most cooperative, and supportive of our efforts. I was provided with full-time
assistance of a student during the time we were in Turkey. This student, Ms. Emine Bulut, and my wife,
Jule, constituted the 'field crew' that assisted with the collection of parasitoids.
Unfortunately, weather in 1997 was unusually cold and wet. I was told that this year Antalya Province,
the area in which we collected, had the coldest April in 106 years. During the time we were in Turkey
(April 4-23), we encountered considerable rain (and snow one day) and cold, especially during the first
two weeks. This disrupted normal insect and plant development, and made collecting much more
difficult than had been anticipated. Instead of being able to send at least one or two shipments back to
the United States during the time we were there, I was able only to bring living material with me when I
returned - as hand-carried baggage. (Of course, all of the necessary state and federal permits and
permission for importation into the United States had been obtained, along with official documentation
from Turkish authorities to clear the shipment.)
As during the collections two years ago, parasitoid adults were associated primarily with second-stage
thrips larvae. Individuals of both sexes of parasitoid were collected with aspirators, held in escape-proof
containers, and provided with a sugar/water solution for moisture and nourishment from collection and
during transit. An employee of the USDA Biological Insect Research Laboratory, Newark, DE, met us on
arrival in Philadelphia and carried the sealed package of insects directly to the quarantine facility
operated by that lab where the package was opened.
The preliminary reports are that at least two species of parasitoids were included in the material (along
with some incidental material that will be identified for the record, but which has no potential for
biological control). Sufficient numbers survived the holding period of from two to seven days overseas,
and transportation, to allow exposure to a thrips colony in the quarantine facility in an attempt to
initiate a laboratory colony. Because the biology of this new species is unknown, we must await
development under laboratory conditions before we can proceed further with studies. So far, the
identity of the second species we collected in some numbers is not known. Once we have an
identification, we will be able more quickly to determine what, if anything, is known about its biology as
well. Still ahead is a series of critical studies to evaluate the potential of any species which is being
considered for release in a new environment to attack native insects. Should the species collected
overseas show evidence that they might attack species other than the targeted pest, extended studies
will have to be undertaken, still in the quarantine facility, before any consideration will be given to
release - even to our laboratory for further laboratory testing. No releases into forested sites will be
approved until thorough evaluation of likely consequences has been completed. This process could take
several years, or might move more rapidly depending on information gained at critical steps of the
investigation. If there is a probability that what is viewed as a 'beneficial' species might cause adverse
impact on native species, permission for release is not likely to be granted.
As progress on these investigations continues, I will keep the Research Committee informed. We have
only just begun what could turn out to be an exciting and valuable effort to assist producers across the
sugar maple region. However, as with any research efforts, there are no guarantees of success. We can
only pursue each next logical step as it comes. I gratefully acknowledge the continuing support of our
program by the Research Committee of NAMSC, the support and assistance of our Turkish colleagues
and friends, and especially the field support and assistance of Emine Bulut and Jule Cameron.
References Cited
Cameron, E.A., and D.A.J. Teulon. 1996. Exploration in Turkey for biological control organisms for the
pear thrips. Maple Syrup Digest 8A(1): 8-11
Cameron, E.A., D.A.J. Teulon, and L.H. McCormick. 1996. Prospects for management of pear thrips
[Taeniothrips inconsequens (Thysanoptera: Thripidae)) in sugar maple (Acer saccharum) forests in the
Northeastern United States. [Abstract] in: Christine SILVY [compiler and editor] International
Conference: 'Technology transfer in biological control: From research to practice.' IOBC WPRS Bulletin
19(8): 182.
Teulon, D.A.J., and E.A. Cameron. 1996. The pear thrips in northern hardwood forests of the
Northeastern United States. Folia Entornologica Hungarica 57 (Suppl.): 143-150.
Teulon, D.A.J., T.C. Leskey, and E.A. Cameron. 1997. Pear thrips (Thysanoptera: Thripidae) life history
and population dynamics in sugar maple in Pennsylvania. Bulletin of Entomological Research [in press].
Teulon, D.A.J., T.E. Kolb, E.A. Cameron, L.H. McCormick, and G.A. Hoover. 1993. Pear thrips, Taeniothrips
inconsequens (Uzel) (Thysanoptera: Thripidae), on sugar maple, Acer saccharum Marsh.: A review.
Zoology (journal of Pure and Applied Zoology) 4: 355-385. Advances in Thysanopterology. Dedicatory
Volume in honour of Prof. Dr. Alexandre Bournier's 80th Birthday (15 Dec. 1993).
Disease - Decay and Stain
Recognizing and Managing Sapstreak Disease of Sugar Maple
Research
United States Department of Agriculture Forest Service
David R. Houston, Northeastern Forest Experiment Station
Research Paper NE-675
October 1993
REF# 014
Abstract
Sapstreak disease is a potentially serious problem of sugarbushes and forest stands. It occurs when the
causal fungus, Ceratocystis virescens, invades the sapwood of roots and bases of stems through wounds
inflicted during logging, saphauling, or other activities. This bulletin describes how to recognize the
disease, the factors that affect its occurrence and development, and management approaches to help
reduce its effects.
The Author
DAVID R. HOUSTON is a principal plant pathologist conducting research on dieback and decline diseases
at the Center for Biological Control of Northeastern Forest Insects and Diseases, a laboratory of the U.S.
Department of Agriculture, Forest Service, Northeastern Forest Experiment Station, Hamden,
Connecticut. For the past 30 years Dr. Houston's research has focused on stress-initiated dieback and
decline diseases of deciduous hardwoods, especially beech, maple, end oak.
The use of trade, firm, or corporation names in this publication is for the information and convenience
of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department
of Agriculture or the Forest Service of any product or service to the exclusion of others that may be
suitable.
Manuscript received for publication 15 March 1993
Cover Photo. Small leaves often are the first obvious symptom of sapstreak disease.
Introduction
Sapstreak of sugar maple (Acer saccharum Marsh) is a disease of the living sapwood incited by the
fungus, Ceratocystis virescens (Davidson) C. Moreau (=C. coerulescens (Munch) Bakshi)
(=Endoconidiophora virescens Davidson) (Hepting 1944). Sapstreak, first noticed in North Carolina in
approximately 1935 (Hepting 1944), has since been reported in Michigan in 1959 (Kessler and Anderson
1960), Vermont in 1964 (Houston and Fisher 1964), Wisconsin in 1971 (Kessler 1972) and New York in
1978 (Bell and Kessler 1979, Houston and Schneider 1982). In each case, the disease occurred in stands
where activities such as logging, road building, or sap hauling had inflicted root or lower stem wounds to
the affected trees. These injuries allow C. virescens to invade and then kill the wood of lower portions of
the stem and roots (Hepting 1944, Kessler 1978, Houston 1985). Because C. virescens is one of the most
common fungi in northern hardwood forests (Shigo 1962), sapstreak disease has the potential to occur
where the roots and lower stems of sugar maple trees are wounded during logging or other activities in
these forests.
This paper presents information on (1) symptoms of the disease, (2) factors affecting disease occurrence
and development and (3) management approaches to reduce disease effects. This information was
obtained from published articles and a series of studies conducted from 1979 to 1991. Details of the
studies are not presented in this paper.
Symptoms of the Disease
Usually, the first observed symptom of sapstreak is a distinctive "transparency" of the tree crown - a
consequence of unusually small leaves, especially in upper branches but sometimes over the entire
crown (Fig.1). Often, these small leaves are normal in color, shape, and number the first year of the
disease, but become off- colored and sparse in subsequent years. Branch dieback often occurs where
small leaves had occurred the previous year, and this pattern of small leaves one year followed by death
of supporting twigs and branches the next, can continue for several years until the tree dies (Fig. 2).
Sometimes, however, symptom progression is arrested and results in trees whose upper crowns exhibit
branch dieback or even major stagheading while lower branches are fully foliated with leaves of normal
size and color. Some of these trees recover with no further disease progression while others, after
several years of apparent remission, again exhibit symptoms.
Figure 1. A thin "transparent" crown with leaves much smaller than normal--the first indication that a
tree may have sapstreak disease.
Figure 2. Progressive branch dieback may occur over several years.
Inside the tree the diseased wood of roots and lower stems exhibits a distinctive stain (Fig. 3). Freshly
exposed, the stain is greenish yellow to yellow-tan with red flecks and appears watersoaked. Often, in
cross-section, the stain columns appear to radiate outward and are bordered by a thin, intermittent,
dark-green margin. Soon after exposure, the stain darkens dramatically, then later fades to a light
brown.
Figure 3. Sapstreak disease stain, when fresh, has a watersoaked, greenish-yellow-to-tan color with
scattered red flecks, and is bordered by a narrow green margin. The stain often appears to radiate
outward.
External symptoms are related closely to development of internal stain. By the time crown symptoms
appear, stain columns are well established (Fig. 4), especially in root tissues, and usually can be revealed
by an ax cut into the buttress roots. In many trees, especially those in remission of crown symptoms, the
outward extension of stain columns appears to be limited by newly-formed rings of healthy sapwood
(Fig. 5).
Figure 4. Well developed stain columns at the root collar and occupying most of the sapwood. By the
time the crown symptoms appear, the stain is well established.
Figure 5. Internal stain column that is well compartmentalized by annual ring boundaries.
When trees infected by sapstreak disease are cut into lumber, the stain columns often are very
noticeable and distinctive (Houston 1986). Within a few minutes of cutting and exposure to air, stain
columns become dark brown (Fig. 6). As drying progresses, the columns gradually change color,
becoming lighter--while the clear wood, in contrast, darkens (Fig. 7). Surface planing of dried lumber
reverses these patterns and again reveals the light brown stain of diseased wood in contrast to the clear,
white, healthy wood.
Figure 6. Boards cut from the log of a sapstreak diseased tree. Note extensive columns of dark
discoloration.
Figure 7. As drying progresses, the dark stain columns fade to a light grayish tan (right side or board)
and healthy tissues gradually darken (left side of board). Note the dark smudgy strip where C. virescens
(large arrow) has grown out onto wood surface near the edge of the stain column, and the blotchy
colonies of saprophytic mold fungi (small arrows) growing exclusively on the sapstreak diseased wood.
When C. virescens grows on board surfaces, where it sometimes sporulates, it usually occurs near the
outer margins of the stain columns and often on clear wood immediately adjacent to stain columns (Fig.
7). The dark, smudgy appearance of the fungal growth is distinctive and develops within a few days of
sawing. As drying continues, the surfaces of the sapstreak stained columns become heavily colonized by
numerous common molds; clear wood remains free of such growths (Fig. 7).
Disease Development within Individual Trees
Infection and Importance of Wounds
Infection occurs primarily through wounds to the roots, buttress roots, or the lower portion of stems
near the ground during logging, saphauling, or other activities (Figs. 8, 9) (Hepting 1944, Houston 1992,
Meilke and Charette 1989). Stump wounds, created when sprout members are removed in thinning, can
provide the fungus access to otherwise unwounded residual members (Fig.10). A few cases have been
observed where the fungus apparently entered the tree through roots injured by cattle trampling.
Figure 8. Basal injuries typical of those on sapstreak diseased trees adjacent to skid trails.
Figure 9. Buttress roots and roots close to the soil surface typical of those damaged by traffic in the
sugar bush; these roots are at risk to infection by the sapstreak fungus.
Figure10. The injury created when one member of a sprout clump was removed served as an infection
court for the sapstreak fungus. Note sapstreak stain revealed by the ax cut at the root collar of the tree.
Injuries associated with sapstreak are nearly always close to the ground. Even though stem tissues can
be infected, and invasion of upper portions of stems from infections originating in the roots or stem
bases can occur, no definitive cases have been found where infection has occurred naturally through
broken branches or other wounds of upper crowns or stems. No cases have been observed where, in
practice, tapholes have become infected by sapstreak, and only rarely (2 of 142 times) did this occur
when the fungus was placed experimentally into tapholes (Houston 1992). In each instanc' where
infection did occur, its development around tapholes was sharply limited by the tree (Fig.11).
Figure 11. A rare instance of sapstreak disease when the fungus was placed in the taphole (arrow); the
fungus was contained by the tree and discolored columns were limited. Spread probably attributable to
tangential orientation of the taphole, which cut across normally effective ray boundaries.
Results from several studies suggest that wounds made in the late spring and early summer may be
more readily infected by C. virescens than wounds made at other times. Other tree species are known to
be most susceptible to vascular pathogens at this time. Meilke and Charette (1989) found no significant
differences in the number of trees affected by sapstreak in Wisconsin stands logged during frozen versus
nonfrozen conditions, although no records were available concerning the number of trees wounded or
the actual conditions of the roadways when logging occurred.
A few cases have been observed where the fungus moved across functional root grafts from wounded,
diseased trees to adjacent, nonwounded neighbors (Houston 1991).
Disease Progression within Individual Trees (Patterns and rates)
Within individual trees, the appearance of initial crown symptoms and the rate of their progression
varies greatly.
Some trees exhibit severe crown dieback for many years before they die, while others become
symptomatic and succumb rapidly, often within 2-3 years. Trees that die quickly and possess severe
symptoms usually are extensively invaded by C. virescens (Fig.12). In most such trees, vascular staining is
present throughout the roots and much of the stems, and the fungus sometimes can be isolated from
xylem tissues in the upper portions of stems, often up to 30-45 ft.
Figure 12. Bolts, 1 meter long, sequentially cut (from root collar up and placed in that order for photo)
from a tree that died within 18 months after being infected with C. virescens. The dark fungus has grown
out from the columns of stained xylem onto the cut ends of the bolts.
Sometimes disease progression, as revealed externally by crown symptoms, is arrested and recovery
ensues, even in trees with more than 40 percent crown dieback. Some trees with root-stain patterns
characteristic of sapstreak disease never developed severe foliar symptoms during the course of a 10year study. In such trees, the columns of discoloration usually appear strongly restricted by the tree
(Fig.13).
Figure 13. In this tree both developing columns of discoloration are limited strongly by
compartmentalization.
Disease development within trees also can be monitored nondestructively. Sapstreak stained wood
characteristically is very low in electrical resistance (ER) (50 K ohms and often as low as 5 to 10 K ohms)
compared to healthy tissue (100-700 K ohms) (Houston and Schneider 1982). Tissues infected by
sapstreak disease can be identified reliably by their ER measurements (Table 1).
Table 1. Comparison of electrical resistance (k-ohms) of buttress-root tissues of a healthy tree and a
tree with sapstreak disease
Electrical resistance (K ohms) - July 1980
Depth (inches) into root wood
Root
.25
.50
.75
1.0
1.25
1.50
1.75
2.0
1
180
190
210
290
260
230
240
200
Healthy 2
250
230
160
210
256
200
260
260
tree
3
500
400
330
280
280
500
300
4
320
220
230
240
240
250
340
500
1
21
34
18
27
22
46
21
-
Diseased
2
15
18
23
17
13
13
9
tree
3
80
80
70
80
70
4
100
80
70
90
50
60
-
Development of the disease usually is more rapid and extensive in roots than stems. Often, extension of
the stain columns into stems is sharply limited even when roots and root collar regions are severely
colonized (Fig.14). Repeated measurements on individual trees reveal the disease pattern in a sugar
maple root system, July 1980 to July 1981 (Table 2).
Figure 14. Sometimes spread of the fungus upward into stem tissues is limited even though tree roots
and root collars are severely colonized.
Table 2. Electrical resistance in two successive years in buttress roots on different sides of a diseased
tree reveal progression of the disease. Numbers below 50 indicate sapstreak disease.
Tree 68: Electrical resistance (k-ohms) of buttress roots
Depth (Inches into rootwood)
Date
Side of
measured
tree
.25
.50
.75
1.0
1.25
1.50
1.75
2.0
July 1980
N
24
45
35
110
80
35
-
-
Symptoms
W
500
500
450
380
300
500
500
-
in extreme
S
450
250
180
170
250
190
380
200
top
40
100
130
150
110
110
190
80
July 1981
N
55
60
70
60
55
65
-
-
Symptoms
W
100
175
45
40
40
38
40
-
same asS
140
180
280
280
210
220
220
190
1980
20
12
12
8
7
6
5
4
E
E
Speed and extent of column discoloration may relate to the severity and orientation of infection court
and other wounds near expanding columns. In some trees, dramatically and greater discoloration occurs
when fungus invades deep wounds across the tangential face of the tree stem or root, compared to
wounds oriented toward the center. Deep tangential wounds disrupt more preestablished compartment
barriers (Shigo 1977,1979). In some trees, however, the fungus is limited regardless of the wound
orientation, suggesting that trees vary in retarding the invasion process.
Finally, other organisms appear to influence the rate at which sapstreak diseased trees succumb. Trees
dying of sapstreak disease almost always are colonized at their roots or root collars by Armillaria sp.
(Fig.15), Xylaria sp. (Pers.: Fr. ) Grev. (Fig.16), or, rarely, both (Hepting 1944, Houston 1985). These root
fungi, ubiquitous inhabitants of long established maple stands, are maintained in root systems of stumps
and dead trees. Root system "food bases" of large trees probably are more important for longer survival
and vigor of root pathogens than are those of small trees whose roots are more quickly consumed.
Although their actual role in sapstreak disease has not been demonstrated, it is likely that these fungi
contribute significantly to the death of sapstreak affected trees.
Figure 15. The thin, white, girdling mycelial "fan" of shoestring root rot fungus, Armillaria sp., beneath
the bark of sapstreak infected tree.
Figure 16. The fruiting structures of Xylaria sp., a root decay fungus often found on trees dying from
sapstreak disease, evoke its common name "dead man's fingers."
The ability of Armillaria spp. to invade and kill trees weakened by stress factors, especially insect
defoliation, is well known (Wargo and Shaw 1985) . Presence of these pathogens and perhaps others,
such as Hypoxylon deustum (Hoffm.: Fr.) Grev. and Ganoderma applanatum (Pers.) Pat., on dying trees
and their apparent absence from severely affected, but recovering trees, suggests that their attacks may
determine which sapstreaked trees die or recover.
Severely affected trees often are attacked by Ambrosia beetles. Initial concentrations usually are near
the buttress roots and lower bole with columns of sapstreak discoloration near the cambium (Fig. 17).
The role of these insects or their fungal associates in the disease is not known; their great abundance in
later stages of disease suggests they hasten the demise of diseased trees.
Figure 17. Long streaks (between vertical split and arrow) of sapwood discolored by sapstreak disease
sometimes occur near the cambium. The cambium touched by these streaks dies, and cankers (not yet
obvious in this recently infected sampling) may form. Often, Ambrosia beetles penetrate these areas
into the underlying sapwood (arrow).
Disease Development in Sugarbushes
In sugarbushes, sapstreak disease rarely results in large numbers of trees dying at one time. Rather, it
appears to affect a few trees, now and again. The following description is based on observations in many
different bushes, in particular, those made annually over 11 years in two typical sugarbushes in northern
New York.
In sugarbushes, sapstreak disease is not related directly to the tapping process but to associated
activities that result in wounds to roots and lower stems. Vehicles or equipment that bruise or cut
shallow or buttress roots to expose sapwood appears the most important factor. The close association
of sapstreak diseased trees to roads used for saphauling in a New York sugarbush is shown in Figure 18.
Figure 18. Locations of sapstreak diseased trees (boxed outlines) and the years when symptoms were
first observed in a New York sugarbush. Main access and saphauling roads (dash lines) lead to the
sugarhouse near plot 6.
In other sugarbushes, sapstreak disease has occurred in trees with roots injured by cattle and by log
skidding. In one instance, a tree, located adjacent to a field, developed sapstreak symptoms a few years
after its roots had been injured when the field was plowed and disked.
Whether the injuries that led to sapstreak disease were made during saphauling or at some other time is
not known. The fact that very few cases of sapstreak have been observed in sugarbushes employing
tubing collection systems could be due either to reduced saphauling traffic or to less traffic at other
times. Regardless of the sap collection system used, the disease often is most severe near the
sugarhouse where traffic and other activities are concentrated (Fig.19). Other factors, including a
possible buildup of the pathogen on wood from diseased trees stacked near the sugar house, also may
contribute to infection of nearby wounded trees. The fungus often is found colonizing (Fig.12) recently
cut surfaces of stumps and logs (Ohman and Kessler 1963, Shigo 1962).
Figure 19. Plot 6 in a New York sugarbush. Numbered trees (large solid circles) became diseased during
the decade of observation (1980-1990).
Disease Development in Forest Stands
In forest stands as in sugarbushes, sapstreak diseased trees usually have severely injured roots or lower
stems. The patterns of occurrence in forest stands, however, usually differ from those in sugarbushes in
ways that reflect the less frequent, but more severe, wound-inflicting disturbance associated with
harvesting operations. In the area within a harvested stand in northern New York that was near the log
landing, 27 trees were found with sapstreak disease in 1985 (Fig. 20). All of these trees were
immediately adjacent to skid trails created when the stand was logged in early summer of 1981. This
"flush" pattern, in which a large number of diseased trees occurs at one time (from infection of wounds
during heavy skidding activity), is in contrast to the occasional infection of trees in some sugarbushes, in
which annual, but less damaging, intrusions into the stand may result in new or repeated wounding of
additional trees.
Figure 20. Locations of sapstreak diseased trees in a forest area in northern New York, a portion of
which was logged in 1981.
In forest stands, sapstreak diseased trees usually exhibit initial symptoms from 3 to 6 years after the
injury-causing event. While the period over which diseased trees dies frequently is more protracted, the
trees that are going to die will have done so within 6 to 8 years after they became infected.
In less heavily trafficked areas within forest stands, or in stands where fewer trees are being harvested,
for example, in improvement cuts or light thinnings, fewer trees are apt to become injured and diseased
(Fig. 21). In general, diseased trees often are concentrated in wet areas where roots are more severely
damaged. Residual members of thinned sprout clumps occasionally are infected by the sapstreak
fungus, apparently through the stump wounds created by the thinning (Figs. 10, 21).
Figure 21. Locations of sapstreak diseased trees in a 30-acre portion of a forest stand in northern New
York. The stand was thinned in 1980. Trees not dead by 1990 are in remission and appear to have
recovered
The following relationships, gleaned from our observations and studies and from earlier work by others,
are pivotal to the development of management guidelines to prevent or reduce losses from sapstreak
disease in sugarbushes and forest stands.
•
There is an almost universal association of wounds and the occurrence of sapstreak disease. The
disease rarely occurs in nonwounded trees (see Forest Stands).
Location
Wounds of great importance are those near the ground--roots, buttress roots, and lower stems.
Wounds of little or no importance are those of branches and upper stems--branch stubs, pruning
wounds, and tapholes.
Causes
Activities that result in wounds (in order of importance) include skidding logs, hauling sap and wood,
building and maintaining roads, thinning sprout clumps, and trampling by cattle.
Timing
Wounds made during spring and early summer may be more important than those made at other times.
Wounded trees, on rare occasion, become diseased when the sapstreak pathogen invades their roots
through functional root grafts with closely adjacent diseased trees.
Trees that die of sapstreak disease also almost always are invaded by root pathogens, especially
Armillaria sp. and Xylaria sp.
These relationships are reflected in the following management options and guidelines for reducing
losses from sapstreak disease in sugarbushes and forest stands.
Management Options and Guidelines to Reduce Losses from Sapstreak Disease
Sugarbushes
Reduce infection courts
•
Avoid wounding of roots, buttress roots, and lower portions of the stem.
•
Employ tubing collection systems when feasible.
•
Use permanent access and haul roads.
•
Avoid travel with heavy equipment during spring-early summer mud season and wet periods.
Avoid creating other infection courts
•
When conducting thinnings or stand improvement operations either leave or take all members
of sugar maple sprout clumps.
Avoid susceptible period
•
Conduct thinnings, stand improvement operations, wood hauling, and other activities that may
result in injuring trees, in late summer, fall, and winter when trees seem to be less susceptible to
infection.
Avoid build-up of Sapstreak disease inoculum
•
Monitor sugarbush to detect diseased trees.
•
Concentrate surveys to trees along roadways and near sugarhouse.
•
Remove diseased trees promptly (see above for best periods).
•
Avoid stacking infected wood near the sugarhouse. If possible, dry diseased wood in large open
areas away from areas where trees are apt to be injured.
Reduce threat from mortality-associated root pathogens
•
Ideally, establish sugarbush at early age to reduce the need to remove large trees in later
thinnings and consequently reduce large stump food bases for root decay organisms.
•
Monitor sugarbush to track populations of defoliating insects. When necessary, arrange to
control outbreaks of insects whose effects will predispose trees to invasion by root pathogens.
Forest Stands
Reduce infection courts
•
Avoid wounding roots, buttress roots, and lower portions of stems.
•
Establish permanent skid trails and haul roads. If possible, use trees other than sugar maple as
bumper trees.
•
Schedule forest operations to avoid mud season or periods when soil is saturated and soft.
•
For stands rich in sugar maple schedule operations to avoid the late spring-early summer period
when trees appear to be most susceptible.
•
Don't thin sugar maple sprout clumps that are pole-sized or larger--leave them all or remove
them all.
Reduce effects of associated root pathogens
•
Monitor climatic factors such as open, cold winters, drought late spring frosts, and biotic factors
such as insect defoliator outbreaks known to predispose trees to root pathogens.
•
When possible, schedule forestry operations to avoid conducting them during, or soon after,
stress events.
Reduce inoculum and losses
•
Revisit stands 4 to 5 years after logging operations to monitor the occurrence of sapstreak.
•
Focus surveys on trees adjacent to skid trails or landings and especially on those trees with basal
skidding injuries.
•
If feasible, remove diseased trees taking care not to create additional new injuries. (See
infection courts).
Literature Cited
Beil, J. A.; Kessler, K. J., Jr.1979. Sapstreak disease of sugar maple found in New York State. Plant Disease
Reporter. 63:436.
Hepting, G.H.1944. Sapstreak, a new killing disease of sugar maple. Phytopathology. 34: 1069-1076.
Houston, D.R. 1985. Sapstreak of sugar maple: How serious is it? Maple Syrup Digest. 25(2): 24-27.
Houston, D.R.1986. Sapstreak of sugar maple: appearance of lumber from diseased trees and longevity
of Ceratocystis coerulescens in air-dried lumber. Phytopathology. 76: 653. Abstract.
Houston, D.R. 1991. Spread of the sugar maple Sapstreak disease pathogen, Ceratocystis coerulescens,
via root grafts between Acer saccharum. Phytopathology. 81:122. Abstract.
Houston, D.R. 1992. Importance of buttress root and taphole wounds as infection courts for the sugar
maple (Acer saccharum) Sapstreak pathogen, Ceratocystis coerulescens. Phytopathology. 82: 244.
Abstract.
Houston, D.R.; Fisher, K.D. 1964. Sapstreak of sugar maple found in the northeast. Plant Disease
Reporter. 48: 788.
Houston, D.R.; Schneider, B. 1982. Sapstreak disease of sugar maple in N.Y. sugarbushes.
Phytopathology. 72: 262. Abstract.
Kessler, K., Jr. 1972. Sapstreak disease of sugar maple found in Wisconsin for the first time. Res. Note
NC-140. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment
Station. 2 p.
Kessler, K., Jr. 1978. How to control Sapstreak disease of sugar maple. St. Paul, MN: U.S. Department of
Agriculture, Forest Service, North Central Forest Experiment Station. 5 p.
Kessler, K., Jr.; Anderson, R.L. 1960. Ceratocystis coerulescens on sugar maple in the Lake States. Plant
Disease Reporter. 44: 348-350.
Meilke, M.E.; Charette, D.A. 1989. The incidence of sapstreak disease of sugar maple in Menominee
County, Wisconsin, and its relationship to wounds and season of logging. Northern Journal of Applied
Forestry. 6: 65-67.
Ohman, J.H.; Kessler, K.J., Jr.1963. Current status of the sapstreak disease of sugar maple in the Lake
States. Res. Note LS-10. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest
Experiment Station. 4 p.
Shigo, A.L. 1962. Observations on the succession of fungi on hardwood pulpwood bolts. Plant Disease
Reporter. 46: 379-380.
Shigo, A.L. 1977. Compartmentalization of decay in trees. Agric. Inf. Bull. No. 405. Washington, DC: U.S.
Department of Agriculture, Forest Service. 73 p.
Shigo, A.L. 1979. Tree decay: an expanded concept. Agric. Inf. Bull. No. 419. Washington, DC: U.S.
Department of Agriculture, Forest Service. 73 p.
Shigo, A.L.; Shigo, A. 1974. Detection of discoloration and decay in living trees and utility poles. Res. Pap.
NE-294. Upper Darby, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest
Experiment Station. 11 p.
Tattar, T.A.; Shigo, A.L.; Chase, T. 1972. Relationship between the degree of resistance to pulsed electric
current in wood in progressive stages of discoloration and decay in living trees. Canadian Journal of
Forest Research. 2: 236-243.
Wargo. P.M.; Shaw, C.G., III. 1985. Armillaria root rot. The puzzle is being solved. Plant Disease. 69: 826832.
Sapstreak Disease of Sugar Maple - Development Over Time and Space
Research
USDA Forest Service
David R. Houston
Northeastern Forest Experiment Station
Research Paper NE-687
June 1994
REF# 016
Abstract
Sapstreak disease is a potentially serious problem of sugarbushes and forest stands. It is caused by the
fungus Ceratocystis virescens, which invades sapwood of roots and bases of stems through wounds
created during logging, saphauling, or other activities. This report describes the results of observations
and experiments to learn more about the patterns of disease development and the factors that affect
them, within individual trees and within representative forests and sugarbushes.
The Author
DAVID R. HOUSTON is a principal plant pathologist conducting research on dieback and decline diseases
at the Center for Northeastern Forest Health Research, a laboratory of the USDA Forest Service's
Northeastern Forest Experiment Station at Hamden, Connecticut. For the past 30 years Dr. Houston's
research has focused on stress-initiated dieback and decline diseases of deciduous hardwoods,
especially beech, maple, and oak.
Manuscript received for publication 20 April 1993
The use of trade, firm, or corporation names in this publication is for the information and convenience
of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department
of Agriculture or the Forest Service of any product or service to the exclusion of others that may be
suitable.
Acknowledgments
Thanks are given to the New York State Department of Environmental Conservation and to the South
Central Connecticut Regional Water Authority (formerly New Haven Water Co.), who provided land and
trees, to numerous maple syrup producers, especially Howard Lyndaker of Beaver Falls, New York, and
to the late Ralph Mantle of Harrisville, New York, who let us prowl, probe, and poke through their
sugarbushes for over a decade. Special thanks are given to Bruce Schneider and Terry Podolski of the
New York State Department of Environmental Conservation and to Eileen Mahoney, Chris Fagan, and
Gerald Walton, U.S. Department of Agriculture, Forest Service, Hamden, Connecticut. Without their
valuable assistance in surveys and experiments, and in statistical analysis, these studies could not have
been conducted. I also wish to thank Eileen Mahoney, Manfred Mielke, Margaret Miller-Weeks, Barbara
Burns, Lewis Staats, Louise Tritton, and Sumner Williams for their reviews of the manuscript.
Introduction
During the course of our research to clarify the stress factors and organisms associated with dieback and
decline diseases of sugar maple, we encountered several instances in which declining trees in managed
forest stands and sugarbushes in northern New York had not been subjected to stresses usually
associated with these problems. The subsequent discovery that a number of these trees were affected
by sapstreak disease suggested that this disease might be causing more loss than previously recognized,
and that management practices were involved.
Background
Sapstreak disease of sugar maple (Acer saccharum Marsh) is a vascular xylem disease incited by
Ceratopystis virescens (Davidson) C. Moreau (=C. coerulescens (Munch) Bakshi). See Smith (1990) for a
nomenclature history of the sapstreak fungus. The disease was first noticed in North Carolina about
1935 (Hepting 1944), then in Michigan in 1959 (Kessler and Anderson 1960), Vermont in 1964 (Houston
and Fisher 1964), Wisconsin in 1971 (Kessler 1972), and New York in 1978 (Beil and Kessler 1979). In
each of these cases, the disease occurred in stands where activities such as logging, road building, or sap
hauling had injured the affected trees.
Injuries apparently allow C. virescens to invade and then kill the xylem of the lower portions of stems
and roots where it creates the distinctive "sapstreak" stain (Hepting 1944, Ohman and Kessler 1963,
Kessler 1978, Houston 1985). The common occurrence of the fungus as a saprophyte on freshly cut bolts
of sugar maple and other northern hardwood species (Shigo 1962) suggests that in managed stands
inoculum is readily available.
The external syndrome begins with leaves that are small and off-color (Fig. 1), continues through
progressive stages of crown dieback, and finally ends in tree death. These stages may ensue rapidly with
trees dying in 1-2 years or the stages may stretch over several years. Kessler (1972) reported that no
symptomatic trees recover.
Figure 1. A thin crown with leaves much smaller than normal, the first indication that a sugar maple tree
may have sapstreak disease.
Inside the tree, the diseased wood of roots and lower parts of stems exhibits a distinctive stain (Fig. 2).
Freshly exposed, the stained wood is greenish yellow to yellow- tan with red flecks and the wood
appears watersoaked. Often, in cross section, the stain columns appear to radiate outward and are
bordered by a thin, dark-green margin. Soon after exposure, the stained wood darkens dramatically, and
later still, fades to a light brown.
Figure 2. The unique stain of the sapwood, which occurs most often in roots and lower stems.
The studies reported here were conducted to learn more about the patterns of disease development
and the factors that affect them, within individual trees and within representative forests and
sugarbushes.
Disease Development In Sugarbushes and Forests
Observations were made annually for up to 11 years in three stands in northern New York State. These
included a sugarbush in Diana, a forest stand near Barnes Corners logged in early summer 1981, and a
second forest stand, also near Barnes Corners, thinned in 1980. While the majority of observations were
made in these areas, numerous sapstreak diseased trees in other sugarbushes and forest stands in New
York and Vermont were also examined, sometimes several times, and records were made of symptoms,
locations, and disturbance histories.
Patterns in the sugarbush. The Diana sugarbush, a 65-acre portion of a mature, pure sugar maple stand,
has been in operation for about 75 years. Sap is collected by buckets (2,000 taps) and hauled by tractordrawn wagons. Summer activity includes felling of diseased or weakened trees and hauling the resulting
wood to be stacked near the sugar house. The disease was observed first in the Diana stand in 1978 and
affected a single tree located close to the sugar house. A survey the next year located four additional
symptomatic trees. Isolations from stained buttress-root tissues yielded C. virescens.
In 1980, six study plots, each containing at least one symptomatic sapstreak-diseased tree, were
established to observe the progress of disease within the symptomatic trees, to observe for patterns of
"spread" from diseased to healthy trees, and to monitor the appearance of symptoms in infected but
initially asymptomatic trees. A seventh plot was established in 1982. Plots varied in size and shape and
contained 15 to 32 trees. The locations of all plot trees > 4.0 in (10 cm) diameter at 4.5 ft (1.4 m) (d.b.h.),
dead trees and stumps, and woods roads were mapped. The d.b.h., crown class, general crown
condition, and the presence or effects of insects and disease agents were noted. The distances from
each tree to haul roads, sapstreak-diseased trees and stumps; and the location, size, and probable cause
of any visible root or buttress wounds were recorded.
In 1979, it was determined that sapstreak-stained wood characteristically was very low in electrical
resistance (ER), (<= 50 K ohms and often as low as 5-10 K ohms), compared to healthy tissue (100-700 K
ohms), and that tissues infected by sapstreak disease reliably could be identified by their ER
measurements (Table 1) (Houston and Schneider 1982). At the outset, and periodically thereafter, ER of
buttress-root wood was measured for each plot tree to detect the presence of stained tissue in
otherwise asymptomatic trees. Measurements were made in up to four roots, one each on opposite
sides of the tree, or until diseased tissue was encountered (Table 2).
Table 1. Comparison of electrical resistance (K-ohms) of buttress-root tissues of a healthy tree and a
tree with sapstreak disease
Electrical resistance (K-Ohms) - July 1980
Depth (inches) into root wood
Root
.25
.50
.75
1.0
1.25
1.50
1.75
2.0
Healthy 1
180
190
210
290
260
230
240
200
2
250
230
160
210
256
200
260
260
3
500
400
330
280
280
500
300
-
4
320
220
230
240
240
250
340
500
1
21
34
18
27
22
46
21
15
18
23
17
13
13
9
11
3
80
80
70
80
70
-
-
100
80
70
90
50
60
Diseased:
-
Symptoms in
1980
2
Alive in 1981
4
-
Table 2. Electrical resistance measurements taken in 2 successive years on different sides of diseased
tree 68 reveals the progression of the disease
Depth (inches) into root wood
Time of Side
.25
.50
75
1.0
1.25
1.50
1.75
2.0
24
45
35
110
80
35
-
-
(Symptoms in W
500
500
450
380
300
500
500
-
extreme top)
S
450
250
180
170
250
190
380
200
40
100
130
150
110
110
190
80
measurement of tree
July 1980
E
N
July 1981
N
55
60
70
60
55
65
-
-
(Symptoms
W
100
175
45
40
40
38
40
-
same as 1980) S
140
180
280
280
210
220
220
190
E
12
12
8
7
6
5
4
20
Annually through 1990, the condition of each plot tree was noted. When possible, photographs were
taken of each diseased tree to provide a visual record of symptom progression. Each year the sugarbush,
in general, was surveyed to detect any additional trees with crown symptoms. If such trees also
possessed ER measurements and stain patterns characteristic of sapstreak disease, their locations in the
stand were mapped and their conditions were followed annually until they died or were cut by the
sugarbush owner.
Results. Locations of the plots and diseased trees are shown in Figure 3. Over the course of this study, 19
trees in the study plots (Table 3) and 4 outside the plots developed foliar and crown symptoms or the
characteristic stain of buttress-root wood and were confirmed as having sapstreak disease. Trees in all
crown classes were affected and ranged in size from 7.0 to 43.6 in (18 to 111 cm) d.b.h. Most trees were
located within 5 ft (1.5 m) of haul roads, although three were 10 ft (3.1 m) away.
Figure 3. Locations and years symptoms were first observed, of sapstreak-diseased trees (black dots),
and stumps (circled dots), in and near study plots in a Diana, New York, sugarbush. Main access and sap
hauling roads (dashed lines) lead to the sugarhouse adjacent to Plot 6.
Table 3. Patterns of symptom expression In 19 sapstreak-diseased trees In a New York Sugarbush, 1979
to 1990
Year
Distance (ft) to:
Plot
Tree
D.b.h. First
no.
no.
(inches) symptoms
cut
1
1
15.7
1979
1984
2.5
2,3,4
2
32
17.6
1979
1981
3.5
2,3
3
51
12.5
1984
Dead, Recovered
(remission)
Diseased
Associated
Road
root rots
tree
4.0
(ER:1980)
59
43.6
1979
60
15.0
1983
1983
(ER: 1982)
3.0
1.57
1
4
68
20.2
1979
5
76
17.0
1981
1982
3.0
2,3
6
95
21.8
1981
1984
2.0
1
98
19.3
1980
1983
10.0
2,3,4
99
16.2
1982
104
24.3
1983
107
16.8
1981
1982
3.0
109
7.0
1982
1987
10.0
112
16.0
1982
120
26.3
1982
121
15.6
1988
128
14.9
1983
7
1980
1983
6.0
8.0
5.0
2.0
1986
1985
1,3
14.0
10.0
7.0
1,2,3
3.0
1986
0.5
(ER:1 982)
133
12.9
1983
4.0
1.0
(ER:1982)
134
17.9
1983
1988
0.5
(ER:1982)
Although diseased trees often occurred and persisted as isolated individuals (Fig. 3: plots 1, 2, 4, 5),
there were several cases where healthy trees relatively close to diseased trees became symptomatic
(Fig. 3: plots 3, 6, 7). For at least two of these cases (Figs. 4, 5), it is quite probable that other diseased
trees had occurred earlier as descriptions provided by the sugarbush owner suggested strongly that
many of the stumps present in these areas were of trees affected by sapstreak.
Figure 4. Study Plot 3 in the Diana, New York, sugarbush. The enlarged section of roadway (within
dashed lines) was deeply ruffed during logging in 1975-1976. Dates represent years crown symptoms or
electrical resistance (ER) measurements revealed sapstreak. "Suspect" stumps are of trees whose
descriptions suggest disease.
Figure 5. Study Plot 6 in the Diana, New York, sugarbush. Numbered trees (larger solid circles) became
diseased during the decade of observation (1980-1990).
Access roads and haul roads dissected the sugarbush, and depressions revealed the locations of many
additional old roads no longer used. Most diseased trees possessed obvious and severe butt and root
injuries attributable to equipment used in hauling sap or skidding logs. However, six trees bore no visible
injury. Five of these were within 6 ft (1.8 m) of a road; the sixth tree, located 10 ft (3.1 m) from a major
access road, was determined later to be connected by root grafts to an asymptomatic diseased tree 0.5
ft (0.1 m) from the road (Fig. 6). The possibility of root-graft transmission was explored later in a
separate study (see inoculation trial 5). Although roadways in this sugarbush were not excavated to
determine if adjacent diseased trees had roots that extended beneath the road and had been wounded,
we observed this to be the case in several forest stands elsewhere. Buttress-root injuries often were
nearly closed over by callus by the time foliage symptoms first appeared.
Figure 6. Study Plot 7 in the Diana, New York, sugarbush. The diseased tree (large arrow), which first
showed symptoms in 1982, had no discernible root or buttress wounds. Soil excavations revealed that
its roots were grafted to the severely wounded and infected tree adjacent to the road (small arrow).
In this sugarbush some of the major access roads had been used earlier for skidding logs. In wet areas,
especially on slopes, skidders caused deep ruts and injured and exposed roots. Plot 3 Fig. 3, Fig. 4 ),
where sapstreak was severe, encompassed a road deeply rutted during the skidding. Sapstreak disease
also was severe near the sugarhouse (Fig. 3, Fig. 5.: plot 6). Over the course of this study, nine trees in
this plot developed symptoms. Although trees in the sugarhouse area suffered the most traffic-related
injuries, other factors (including a possible buildup of the pathogen on wood from diseased trees
stacked near the sugarhouse) also may have contributed to infection of nearby wounded trees.
Patterns in forest stands. Disease development was followed in two forest stands on the Tug Hill Plateau
near Barnes Corners, New York. The first of these (stand 1) was a red maple-sugar maple-ash stand
(basal area: 120 ft2/acre; 25 percent sugar maple), a portion of which had been harvested for sawlogs in
early summer of 1981. The second (stand 2) was a sugar maple- beech stand (basal area: 131 ft2/acre;
80 percent sugar maple) thinned during 1980.
In stand 1, skid trails radiating from the log landing site were numerous and deep. A survey in 1984
disclosed 25 trees with crown symptoms, stain, and ER readings characteristic of sapstreak. Two
additional trees developed crown symptoms by July 1985.
All of these trees were adjacent to skid trails (Fig. 7) and all bore severe buttress or root wounds, or
both. No diseased trees were found in nontrafficked portions of the stand.
Figure 7. Locations of sapstreak-diseased trees in forest stand 1 near Barnes Corners, New York, a
portion of which was logged in 1981.
Other trees, in areas where the stand was opened severely and where water tables were high, also
exhibited crown dieback, but lacked the internal sapstreak stain. While some of these trees had basal
injuries, most did not, and many were not situated adjacent to skid trails. A few of these trees died
during the observation period, but many recovered as they adjusted to the changed stand environment.
Twenty of the twenty-seven sapstreak diseased trees in this stand (10 in October 1984, 10 in May 1986)
were felled and sawn into boards to determine the internal patterns of colonization (stain), the
association of C. virescens with the stain, the persistence of C. virescens in air-dried lumber, and the
appearance of diseased wood as it dried (Houston 1986 Six of the remaining seven diseased trees were
dead by October 1985. All of these also were heavily colonized subcortically at their root collars by
Armillaria sp.
In stand 2, sapstreak-affected trees were scattered over the 30-acre area (Fig. 8). Relatively few (112)
symptomatic trees were discovered, and although they occurred on both upland and lower sites, five of
them were concentrated in one lower and wetter area. Four diseased trees without obvious buttress or
root wounds were residual members of sprout clumps. Stumps created when the sprout members were
removed apparently served as infection courts; similar cases were found in two other New York stands
where released, but otherwise unwounded, sprout members were affected by sapstreak disease.
Figure 8. Locations of sapstreak-diseased trees in a 30-acre portion of forest stand 2 near Barnes
Corners, New York. The stand was thinned in 1980.
Patterns within individual sugarbush and forest trees. Within individual trees, the appearance of initial
crown symptoms and the rate of their progression varied greatly (Table 3). Some trees with severe
crown dieback, including some with but a few branches alive, survived for 5-6 years before they died,
while others became symptomatic and succumbed rapidly, often within 2-3 years. Repeated
measurements of ER on some individual trees revealed the progression of the disease. The pattern of
development from July 1980 to July 1981 within the root system of tree 68 is shown in Table 2. Several
very severely affected trees were harvested by the owner before they died; Disease progression, as
revealed externally by crown symptoms and internally by ER measurements or root dissections, was
arrested, and recovery ensued in several symptomatic trees (two with a 40 percent crown dieback). At
least three trees in the sugarbush, and two in forest stand 2, with root-stain patterns and ER
measurements characteristic of sapstreak disease never developed severe crown foliar symptoms
during the course of the study.
Usually, the first observed symptom of sapstreak was a distinctive "transparency" of the tree crown, a
consequence of the presence of unusually small leaves, especially in upper branches, but sometimes
over the entire crown (Fig. 1 ). Often, these small leaves were normal in color, shape, and number the
first year, but became off-colored and sparse in subsequent years. Branch dieback often occurred where
small leaves appeared the previous year, and this pattern of small leaves one year followed by death of
supporting twigs and branches the next sometimes continued for several years until the tree died.
Sometimes, however, symptom progression was arrested and resulted in trees with upper branch
dieback or even major stagheading and lower branches fully foliated with leaves of normal size and
color. While some of these trees apparently recovered with no further disease progression, others, after
several years of apparent remission, again exhibited symptoms.
External symptoms were related closely to development of internal stain, Stain columns were well
established, especially in root tissues, by the time crown symptoms appeared. In many trees, especially
those in remission of crown symptoms, stain columns appeared to be contained by newly formed rings
of healthy sapwood.
Associated organisms. In the sugarbushes and forest stands studied here, and in many others as well,
trees dying of sapstreak disease also were almost always colonized at their roots or root collars by the
root disease pathogens Armillaria sp., Xylaria sp., or, rarely, both (Table 3). This association was noted by
Hepting (1944). Although their actual role in the disease has not been demonstrated, it is likely that
these fungi contribute significantly to the death of affected trees. Their consistent presence on dying
trees and their apparent absence from severely affected but recovering trees suggests that their attack
may determine which sapstreak-affected trees die or recover.
Severely affected trees often were attacked, sometimes heavily, by one or two species of Ambrosia
beetles. These attacks usually were concentrated, at least initially, near the buttress roots and lower
bole. What role, if any, these insects or their fungal associates play in the disease is not known, but their
appearance in later stages of disease development suggests that they probably are not vectors of C.
virescens, but may hasten the demise of severely diseased trees.
Patterns within artificially inoculated trees and saplings. The preceding observations revealed much
about the patterns of occurrence of diseased trees and of the factors that contributed to them. A
considerable amount was learned about the progression of the disease within symptomatic trees. Even
so, many questions pertaining to stand management remained unanswered. Some of these questions
were addressed in a series of inoculation trials that were conducted with saplings and trees to provide
information needed for developing management guidelines. Specifically, these studies attempted to
determine:
•
The nature and rate of symptom expression and disease development in saplings and trees
beginning with the first infection,
•
If trees are more susceptible or vulnerable to the disease at different seasons of the year,
•
If the common stress factor, defoliation, directly influences susceptibility or vulnerability to
sapstreak,
•
If the rate or extent of sapwood colonization is affected by the nature (orientation) of the
wound,
•
If sapstreak disease can spread through root grafts, and
•
If tapholes serve as infection courts for C. virescens.
The nature of symptoms, the rate of disease development, and the relationship of season of infection
and of defoliation stress to susceptibility and vulnerability were addressed in Trials, 1, 11, and 111; the
influence of wound orientation on disease development within individual trees in Trial IV; the spread of
the pathogen through root grafts in Trial V; and the role of tapholes vs. buttress-root wounds as
infection courts in Trial VI.
TRIAL I (Symptom development, rate of disease development, season of inoculation vs. susceptibility
and vulnerability)
• Materials and Methods. Two groups of saplings 2-4 in (5-10.2 cm) in diameter were used. The first
group was growing in the understory near the edge of a stand of pole-size maple trees in southern
Connecticut. This group of saplings was composed of single stems of seedling origin. The second group,
growing about 50 ft (15 m) from the first, consisted of double stems of sprout origin that developed
after a portion of the seedling grove was cut and thinned approximately 10 years earlier. The pole-size
trees used in trial I were scattered within the stand and ranged in size from 7.5 to 10.0 in (19.0-15.4 cm)
in diameter and were of intermediate or codominate crown class. The stand containing the trees and
saplings used in Trial I was defoliated severely by gypsy moth (Lymantria dispar) in the summer of 1981.
Although not observed, It must be presumed that the maples used in these studies had been defoliated
to some degree.
Inoculum for these and subsequent trials was prepared by growing isolates of C. virescens obtained
from sapstreak diseased trees on a sterile wheat grain medium for 10-14 days. Groups of 10-20 saplings
or sprouts were inoculated in November 1981 (10), May (20) and November (10) 1982 and June 1983
(20) by forcing inoculum into a 0.375-in (0.95-cm) -diameter hole drilled horizontally nearly through the
stem at 6 in (15 cm) above ground. Bark and drill bit were sterilized before drilling by scrubbing or
dipping with 95 percent ETOH. Drill holes, filled with inoculum or with sterile wheat grains for controls,
were covered with masking tape. One member of each sprout clump was treated similarly. Fifteen polesize trees were inoculated in May 1982 and 10 more in June 1983 by forcing inoculum or sterile grain
into two 0.375-in (0.95-cm)-diameter holes drilled 2 in (5.1 cm) deep into buttress roots on opposite
sides of the tree.
TRIAL II (season of inoculation vs. susceptibility and vulnerability)
• Materials and Methods. Beginning 1 July 1983, groups of 10 saplings each, growing in the understory
of a second stand, were inoculated as above at intervals of approximately 2 weeks (1 July through 18
October 1983; 5 March through 3 July 1984) or of 4 weeks (10 November 1983 through 5 March 1984).
For both trials, all inoculated plants were examined for symptom expression and disease development
at least once each growing season through 1990. ER measurements were made in buttress roots or
lower stems of all trees with symptoms. Stems and buttress roots of all trees, and of representative
saplings and sprouts that died, were dissected to determine the internal patterns of disease. Isolations
were attempted from the tissues of all the pole-size trees that died, For saplings and sprouts, however,
re- isolation attempts were made only for those that died shortly after inoculation. In saplings and
sprouts that died more than a year after being inoculated, sapstreak-killed tissues usually were too
decayed to support the pathogen.
• Results. In Trial I the rates of disease development, expressed as onset of foliar and crown symptoms
and the occurrence of mortality, varied markedly with tree size (saplings and sprouts vs. pole-size trees),
season, and year of inoculation. Moreover, the nature of symptoms between trees of the same
inoculation series also was remarkably varied.
Nine of twenty saplings and 7 of 20 sprouts inoculated in May 1982, died within 1 year, and of these, six
of each group exhibited complete wilt and death within 2 months. Proportionately fewer saplings or
sprouts inoculated at other times during this trial developed symptoms and died (Fig. 9). In contrast,
none of the 15 pole-size trees inoculated in May 1982, developed symptoms before leaf drop in 1982.
However, by 18 months, six of these trees had developed crown symptoms and died. One of these trees
did not leaf out in 1983, one flushed and then died suddenly in June, and another, which flushed
normally, became increasingly chlorotic, then brown, and died in August. Two more of these trees had
died by 1990.
Figure 9. Percent of saplings, sapling sprouts, or pole-size trees that died in 1987 and 1990 following
inoculation on four different dates. Ratios indicate number died of number inoculated.
Only 2 of 60 non-inoculated members of sprout clumps died even though they shared a common, and
sometimes infected, root system. And, in contrast to the single- stem saplings, which continued to die
through 1990, mortality among sprouts occurred only during the first 4 years after inoculation (Fig. 9).
Dissection of saplings and trees that died or possessed severe symptoms revealed extensive invasion of
roots and often of stems by C. virescens. In most trees, vascular staining was present in, and the fungus
was recovered from, xylem tissues in upper portions of stems often to 30-45 ft (10-15 m) above ground.
As in naturally infected trees, dead or dying inoculated saplings and trees were attacked severely by
Armillaria or Xylaria, or both. Also, as in naturally infected trees, inoculated trees and saplings dying of
sapstreak frequently were infested, sometimes heavily, by one or more species of Ambrosia beetles.
Attacks were concentrated primarily at the bases of the trees near, and especially below, the points of
inoculation. Occasionally, however, these attacks occurred higher up the stems into streaks of
sapstreak-killed xylem tissue that were close to the cambium.
In Trial II mortality patterns of saplings inoculated at different times during the season (July 1983 to July
1984) suggest that trees may be more susceptible or vulnerable to infection and disease development at
particular times of the year (Figs. 10, 11).
Figure 10. The pattern of annual mortality within 20 groups of 10 saplings, each inoculated at biweekly
or monthly intervals from July 1983 to July 1984.
Figure 11. The pattern of cumulative mortality, by years after inoculation, among five groups of 40
saplings inoculated at five different seasonal periods.
Mortality was highest (from 5 to 8 of 10) among each of the four sapling groups inoculated from early
July through mid-August 1983, was lowest (from 0 to 3 of 10) among the four groups inoculated from
late August 1983 through early April 1984, and then increased (with two exceptions) to from 4 to 5 of 10
in groups of trees inoculated from mid-April to early July 1984 (Fig. 10). The somewhat lower death rate
among trees inoculated during 1984 compared to 1983 may reflect, at least in part, the 1 - year shorter
observation period given this group. When the 200 saplings were sorted into five groups of seasonal
inoculation times, mortality patterns ranged from a low of 2.5 percent (1 of 40) in winter months to a
high of 52.5 percent (21 of 40) in the summer (Fig. 11).
TRIAL III (Defoliation stress vs. susceptibility and vulnerability). The high mortality rate among trial I
saplings and trees inoculated in May 1981 (Fig. 9), the first and second growing season after they had
been defoliated severely by gypsy moths, prompted a trial to determine if defoliation stress before or
after inoculation with C. virescens increased sapling and tree susceptibility or vulnerability.
• Materials and Methods. Eighty saplings, 2-3 in (5-7.6 cm) in diameter, growing in a more open portion
of the same stand utilized in Trial 11, were inoculated with wheat grain inoculum as described in Trial 1;
40 on 15 May 1985, and 40 on 28 April 1986. Half of both groups were defoliated completely by hand on
14 June 1985 (a time chosen to reflect the period of peak defoliation activity by the gypsy moth).
• Results. The mortality of the trees in each of the four groups of 20 saplings through 1991 is shown in
Figure 12. By August 1990, more of the saplings inoculated in May 1985 had died (16=40 percent) than
those inoculated a year later (6=15 percent). No additional trees succumbed in 1991. Defoliation had no
effect on mortality rates for the trees inoculated in 1985, equal numbers of trees died in each category.
For those trees inoculated in 1986, however, only one of the defoliated trees died compared to five of
the nondefoliated series. Apparently, defoliation has no direct effect on resistance to C. virescens.
Figure 12. Percent mortality over time, within two groups of 20 defoliated, and two groups of 20
nondefoliated saplings inoculated with C. virescens.
TRIAL IV (Wound orientation vs. pattern of disease development within individual trees). In a number of
earlier studies, dissection of sapstreak-diseased trees revealed that the patterns and extent of sapstreak
discoloration within individual trees varied considerably (Houston 1991, 1986, 1985). The extent of
discoloration and decay within living trees following wounding is known to be related, in part, to the
ability of trees to compartmentalize wounded tissues. One factor that influences this ability is the
orientation of the wound relative to natural barriers within the tree, especially those created by annual
rings and vascular rays (Shigo 1977, 1979). A small study was conducted to determine whether
orientation of infection courts affects the pattern and extent of sapstreak development within individual
trees.
• Materials and Methods. In July 1988, 10 trees,. 4-6.7 in (10-17 cm) d.b.h., were inoculated with C.
virescens. Wheat grain inoculum was introduced into increment borer holes. One hole made at 4.5 ft
(1.4 m) was oriented radially, through the pith center and thus intersected relatively few vascular ray
boundaries. The second hole, made at 3.25 ft (1.0 m) and oriented tangentially to the pith, intersected
and thus disrupted nearly all of the vascular rays on one side of the tree.
Five of the ten trees were harvested after 1 year (7 June 1989), and five after 2 years (25 July 1990).
Stems were sectioned at 4or 8-in (10 or 20 cm) intervals from ground line through each of the
inoculation wounds and above until stain columns disappeared. Photographs made of the ends of
sections were used to characterize the cross-sectional patterns and linear extent of stain associated with
each inoculation wound. The heights of the stain columns were rounded to the nearest 2 in (5 cm).
• Results. None of the inoculated trees developed foliar symptoms before they were harvested. The
extent and crosssectional patterns of the stain columns resulting from invasion by C. virescens varied
considerably between trees (Table 4). Columns associated with the tangentially oriented wounds
generally were greater, both in cross section and in linear extent than those associated with radially
oriented wounds. In a few trees, these differences were striking (trees 5, 6); while in some, (trees 3, 4,
10) the columns were limited in development regardless of wound orientation.
Table 4. Comparison of the pattern and extent of colonization by C. virescens of stem tissues, wounded
radially or tangentially
Height of stain above
Tree
D.b.h. Date
Radial Tangential
No.
(cm)
harvested
wound (cm)
1
11.2
6/89
65
85
+ + +(both somewhat limited)
2
9.9
6/89
55
55
++++
3
10.2
6/89
35
35
+ + (both quite limited)
4
10.3
6/89
35
45
+ + (both quite limited)
5
12.8
6/89
35
85
+++++
Average (1 year)
45
wound (cm)
Stain
61
6
15.5
7/90
95
105
+++++
7
17.2
7/90
?
?
++++
8
14.5
7/90
70
90
++++
9
10.5
7/90
50
85
+++
10
11.6
7/90
25
25
+ (both strongly limited)
Average (2 years)
60
76
The dramatically greater colonization in this study of wounds that disrupted more of the tree's preestablished compartment barriers suggests that the type of wounds created in logging or sap hauling
can influence disease incidence and severity in a major way.
TRIAL V (Root graft transmission of C. virescens). As mentioned previously, a few of the sapstreakdiseased trees observed did not possess the usually obvious root or lower stem wound infection courts.
Observations in permanent plots (Fig. 6, Fig. 7 ) suggested that some of these trees may have become
infected when the fungus moved into their roots across root grafts with adjacent diseased trees. An
experiment was conducted to determine if root-graft transmission does occur and if so, whether it is an
important consideration in management of this disease. A preliminary report has been published
(Houston 1991).
• Materials and Methods. In 1987, 10 pairs of healthy pole-size sugar maples growing in forest stand 1
near Barnes Corners, New York, were selected for the study. Members of each pair were growing in
close proximity (6 to 10 ft, 1.8 to 3.1 m) and, as revealed by careful excavation, were connected by
presumably functional root grafts. Electrical resistance (ER) measurements were made (Shigometer with
twisted wire probe) in the roots on both sides of the graft as well as in the major buttress roots of the
trees to assure that they were healthy at the time of inoculation. In July 1987, one tree of each of five
pairs of trees was inoculated with C. virescens. Inoculated roots included the grafted root and all major
buttress roots. The second group of five pairs was treated similarly in July 1988.
A conidial isolate of C. virescens selected for its tolerance to 2 ppm MBC (benomyl), obtained originally
from diseased tissue (tree 1. plot 1, Fig. 3), was used. Use of this marked isolate made it possible to
determine later whether infection and colonization had resulted from our inoculations or from natural
"wild" inoculum. Inoculum consisted of 2-week-old cultures grown on and mixed thoroughly with a
wheat grain substrate.
Bark surfaces were scrubbed briefly with water to remove dirt and then with 95 percent ETOH (ethyl
alcohol). When dry, 0.25-in (016-cm)-diameter drill holes 2 in (5.1 cm) deep were made and filled with
inoculum. Drill holes were covered with masking tape. Sketches were made of the excavated roots and
inoculation points before roots were covered with soil and loose litter (Fig. 13).
Figure 13. A representative diagram of two sugar maple root systems showing location of potential root
grafts between the systems, the points of inoculation on one of the tree's roots, and the pattern of
discoloration caused by C. virescens following its introduction.
In June 1990, the root systems of both trees in each pair were re- excavated, then dissected to
determine the extent of infection and colonization. Root samples were taken for re-isolation of the
pathogen where ER measurements or stain patterns, or both, suggested that the fungus had moved
across the grafts. When stain columns extended above stump height, trees were felled and dissected to
determine the height of the stain columns.
• Results. Results are presented in Table 5 and Figure 13. Eight of the ten inoculated trees of each pair
were infected (determined by crown symptoms, ER measurements, characteristic stain, and re-isolation,
or both (Table 5). In three of these cases, C. virescens moved across the root grafts to the uninoculated
member of the pair (Table 5, Fig. 13) (determined by crown symptoms, ER measurements, stain
patterns, and re-isolation and growth of the marked isolate on malt agar amended with 2 ppm
benomyl). Grafts between three of the remaining infected and uninoculated pairs were found to be
nonfunctional.
Table 5. Infection success, rates (extents) of colonization, and movement across root grafts in trees
inoculated with C. virescens
ER (K-Ohms)
Infec- Cross- Height
Year
-Pair
Tree
1
symptoms -
of stain
(+,-)
(cm)
Remarks
1988
1989
Inoc.
1987
140-175
dead
+
115-700
15-50
+
200-400
27-190
+
120-130
40-100
+
2
I
symptoms - 1988
1987
NI
(+,-)
over
inoc.
N-Inoc.
1988,1989,1990
1990
tion
905
+
+
Crown
600
27
Crown
79
No symptoms
1989,
1990
3
I
1987
NI
4
I
1987
NI
160-350
60-190
-
214-440
90-140
-
17-80 16-30
290-500
+
40-50
+
No infection
-
208
No symptoms - 1988
+
390
Symptoms on
1, 1989,
and on both in 1990
5
I
1987
NI
6
I
NI
2-100 20-30
420-600
1988
+
43
70-200
Infection did not move
into graft root
10-70 33-43 +
384
990-170
-
99-236 -
Nonfunctional graft
7
I
1988
NI
6-18
+
25
Infection reached graft
150-250
but no cross-
over
8
I
1988
NI
9
I
1988
NI
10
infection
I
NI
1988
6-108 10-50 +
-10
Infection well contained
130-140
-
-
83-250 10-29 +
22
Infection well contained
176-235
200-250
-
186-300
200-250
-
300-350
200-250
-
200-250
No
Dissections revealed that disease development within the inoculated trees varied greatly (Table 5). Thus,
infection did not occur at all in two trees; colonization was strongly restricted and extended only a few
cm in others; colonization in others was extensive with stain columns extending several m in length. In
two of the three tree pairs in which graft transmission occurred, infections within the inoculated trees
were less extensive than within the trees to which they spread (Fig. 13). The variable response by
individual trees to inoculations made on the same day in the same way, and with the same inoculum,
supports results of others (Shigo et al. 1977) that the ability of trees to compartmentalize injuries and
infection by fungi is under strong genetic regulation.
The results of this experiment showed that root grafts between trees growing in close proximity can
serve as conduits for the sapstreak pathogen. However, the relatively low occurrence of transmission in
this study, together with the low incidence of diseased pairs and of nonwounded diseased trees in
nature, suggest that infection through root graft is much less important than direct infection through
wounds above ground.
TRIAL VI (Tapholes vs. buttress wounds as infection courts for . virescens). The relatively high incidence
of sapstreak in some sugarbushes prompted a study to determine If tapholes serve as infection courts
and If so, how important are they compared to other wounds inflicted during sap hauling or other
activities. A preliminary report has been published (Houston 1992).
• Materials and Methods. In 1984, 34 groups of 10 intermediate- codominant sugar maples, 6-8 in (1520 cm) d.b.h. growing in a 15-acre stand near Barnes Corners, New York, were wounded and inoculated
as follows:
Treatment 1 (One open taphole and one taphole with a metal spout): At one of two dates (14 March, 17
April), two 7/16-in (0.43- cm)-diameter tapholes, 2.0 in (5.0 cm) deep, were made on opposite sides of
the trees. One taphole (chosen at random) was left open; a standard metal spout was inserted in the
other. Both tapholes subsequently were inoculated by atomizing into them 2 ml of a conidial
suspension of C. virescens containing 150,000 to 600,000 spores per ml. Controls consisted of trees with
non-inoculated tapholes. Groups of 10 trees each were inoculated once, either when tapped or at
weekly intervals thereafter, until 31 May (Table 6).
Table 6. Schedule of wounding and inoculation, and resulting infection for trees inoculated with 2 ml
conidial suspension into one taphole with metal spout and one open taphole
Treatment 1
Number trees Number
Date tapped
Date inoculated harvested
(1984) (1989-90)
14 March
14 March
infected
5
19 March
5
0
26 March
5
0
9 April 5
0
2 May 5
0
31 May 5
0
Controls
5
17 April 17 April 5
0
23 April 5
1
2 May 5
0
31 May 5
0
Controls
5
0
0
0
tapholes
Treatment 2 (Closed tapholes--plastic spouts with tubing): Tapholes were made in six groups of 10 trees
as described above and plastic spouts fitted with 12-in (30-cm) lengths of plastic tubing were installed in
both tapholes. The tubing was clipped back onto the spout to form a loop. Sap-filled loops served to
maintain a closed system characteristic of tubing systems. Tapholes were inoculated as above
immediately after spouts were removed on 2 or 31 May (Table 7). Controls were tapped but not
inoculated.
Table 7. Schedule of wounding and inoculation and resulting infection for trees inoculated with 2 ml
conidial suspension in each of two tapholes with plastic spouts and tubing
Treatment 2
Number trees Number
Date tapped
Date inoculated harvested
tapholes
(1984) (1984) (1989-90)
infected
14 March
0
2 May 5
31 May 5
0
Controls
5
17 April 2 May 5
0
31 May 5
0
Controls
5
0
0
Treatment 3 (Buttress root injuries): On different groups of 10 trees each, two buttress roots, one each
on opposite sides of the tree, were injured at approximately weekly intervals (Table 8) by bruising them
with a heavy mallet. On one bruise the bark was removed; on the other the bark was broken and
loosened but not removed. Approximately 2 ml of the previously described spore suspension were
atomized onto the wounds immediately after they were made. Control trees were injured but not
inoculated.
Table 8. Schedule of wounding and inoculation and resulting infection for trees inoculated with 2 ml
conidial suspension into two buttress-root bruises
Treatment 3
Date wounded Number trees
and inoculated harvested
Number
(1984) (1989-90)
trees infected
14 March
5
0
19 March
5
0
26 March
6
0
9 April 5
0
2 May 5
3a
31 May 5
4a
8 June 5
0
15 June 6
1a
Controls
14 March
6
31 May 5
0
0
a Five of eight infected trees were infected through both wounds.
Treatment 4 (Root injuries): One group of 10 trees was treated on 31 May by atomizing a spore
suspension onto ax cuts made on an excavated root approximately 2 ft (0.6 m) from the tree. The root
was then covered with forest floor litter. Control trees similarly were injured but not inoculated.
Treatments 5 and 6 (to check on the pathogenicity of the inoculum isolate used (Table 9)): In treatment
5 groups of 10 trees each were inoculated on 14 March, 17 April, or 31 May by forcing wheat-grain
inoculum into two 0.25-in-diameter holes drilled 2 in deep into buttress roots on opposite sides of the
tree. Holes were covered with masking tape. In treatment 6, one group of 10 trees was inoculated on 31
May by filling the drill holes with the conidial suspension used to inoculate tapholes and buttress
bruises.
Table 9. Schedule of wounding and inoculation and resulting infection for trees inoculated with wheat
grain inoculum (treatment 5) or conidial suspension (treatment 6) In two, 0.25-in-diameter holes drilled
2 in deep into buttress roots
Treatment 5
Date wounded Number trees
and inoculated harvested
Number trees
(1984) (1989-90)
infected
14 March
5
1
17 April 5
2
31 May 5
4
Treatment 6
31 May 5
4
Annually, from 1985 through 1989, each tree was observed for presence of foliar symptoms or other
evidence of infection (poor wound closure, exudation from wounds, canker development near wounds).
In June 1989 or July 1990, 5 of the 10 trees within each treatment group were randomly selected and
examined for the presence of sapstreak. Trees in treatments 1 and 2 were felled and cross sectioned
through the tapholes and at 20.0in (0.5-m) intervals above and below the tapholes to observe radial
patterns of discoloration. Sections were split longitudinally to trace the linear extent of the discolored
column associated with each taphole. Column lengths were measured to the nearest cm. Photographs
were taken of the discoloration present in all dissected trees. Inoculated roots were excavated and
dissected to determine presence and extent of infection.
Trees in treatments 3, 5, and 6 were felled, cut through the buttress-root bruises or drill holes to expose
the cross-sectional infection patterns, and dissected to reveal the upward linear extent of infection.
• Results. No trees developed foliar symptoms characteristic of sapstreak during the 5-year observation
period. Closure of both inoculated and non-inoculated tapholes proceeded at an apparently normal
rate, although it was more rapid for tapholes without spouts. Some of the basal injuries exhibited
cambial dieback, and on some trees sprouts developed near the inoculated injuries.
Incidence: Very few tapholes (3 of 146 examined) showed evidence of infection by C. virescens (Table 6,
Table 7). None of the trees in treatment 1 tapped on 14 March and inoculated then or later through
open tapholes or metal spouts developed sapstreak. Controls also were not infected. Two trees in the
series tapped on 17 April had stain patterns that, while limited, were suggestive of sapstreak (Figure 14).
One of these had been inoculated on 23 April, the other was the open taphole of a non-inoculated
control tree. Similarly, in treatment 2 none of the trees tapped on 14 March and inoculated later when
the spouts and tubing were removed, nor their non-inoculated controls, developed sapstreak. However,
one of the trees tapped on 17 April and inoculated on 31 May had discoloration about one taphole
suggestive of sapstreak (Fig. 15). The tangential orientation of this taphole may account in part for the
stain patterns (Trial IV).
Figure 14. "Breakout" pattern of stain around taphole wound "w", suggestive of sapstreak (cross section
cut through the taphole); and the associated column of discoloration (radial section split through the
discolored column).
Figure 15. A rare instance in which sapstreak disease occurred when the fungus was placed in the
taphole (arrow); the fungus was contained by the tree and discolored columns were limited. The
apparent ability of the fungus to spread from taphole "E" probably is attributable to the tangential
orientation of the taphole, which cut across normally effective ray boundaries.
Incidence of sapstreak infection in trees inoculated through buttress-root bruises (treatment 3) was
considerably higher than through tapholes (Table 8). And infection was influenced strongly by treatment
date. While no infection occurred in trees wounded and inoculated on 14, 19, 26 March, or 9 April, three
of five, four of five, and one of five trees wounded and inoculated on 5 and 31 May and 15 June,
respectively, were infected. Of these eight infected trees, five were infected through both bruise
wounds. None of the wounded, non-inoculated trees was diseased. Infection ranged from being strongly
limited in some trees (Fig. 16) to extensive in others (Fig. 17). However, even in trees where extensive
infection in roots had occurred, upward spread into stems was restricted to a few centimeters.
Figure 16. In this tree, both developing columns of discoloration are limited strongly by
compartmentalization.
Figure 17. The discoloration pattern in this tree indicates that C. virescens rapidly invaded the sapwood
following infection through bark bruises.
Two of the five trees inoculated through ax cuts into the roots (treatment 4) developed stain columns
characteristic of sapstreak disease. Both were strongly limited and had spread only a few cm from the
inoculated wound. None of the controls had stains suggestive of the disease.
Rates of infection in the trees inoculated through drill holes in their buttress roots (treatments 5 and 6)
were high (Table 9), especially in trees inoculated in late May. Of the examined trees wounded and
inoculated with wheat grain inoculum on 14 March, 17 April, or 31 May, one of five, two of five, and
four of five, respectively, were infected. Infection occurred through both wounds on six of these seven
trees, Of the five trees examined whose drill hole wounds had been inoculated with conidial
suspensions on 31 May, four were infected, three through both wounds. As in trees infected through
bruised bark, the extent of colonization ranged from slight to severe.
The lengths of the discoloration columns (not related to sapstreak infection) associated with tapholes
(treatments 1 and 2) were analyzed statistically to determine if there were differences between
inoculated and non-inoculated tapholes attributable to wound date, treatment, or inoculation date.
Results are presented in Table 10. Columns of discoloration associated with inoculated tapholes were no
longer than those of the controls. However, significant differences did occur that were related to
treatment and to the date of tapping:
• The mean length of discoloration columns about open or metal- spout tapholes (n=30) (treatment 1)
was significantly longer (P=0.009) than that about closed, plastic-spout tapholes (treatment 2).
• Within treatment 1, the mean length of the discoloration columns about open tapholes; (n=59) was
significantly greater (P=0.01 3) than that about tapholes with a metal spout.
• Columns of discoloration about tapholes made on 14 March were longer than about those made on 4
April. This was significant for treatment 1 tapholes (P=0.02, n=30) but not for treatment 2 tapholes
(n=61).
Thus, the mean discoloration lengths reflect gradients of taphole "openness" and time. The more open
the taphole, and the longer it existed before resumption of physiological activity, the longer the columns
were.
Table 10. Comparison of lengths of discoloration in treatments 1 and 2 (A), the influence of tapping date
(B,C,D) and of open vs. metal spout (E)
Tapholes
(no.)
column length
(cm)
A.
Average
SD
All treatment 1 30
P
67.23 17.86
vs.
All treatment 2 40
B.
C.
0.009
50.62 12.83
All treatments 1+2:
14 March
60
62.30 18.24 0.098
17 April 64
55.48 13.03
Treatment 1 only:
14 March
30
72.17 18.58 0.020
17 April 30
57.73 13.01
D. Treatment 2 only:
14 March
32
50.81 12.98 0.83
17 April 32
53.37 13.11
E.
Treatment 1 only:
Open
59
Metal 61
34.02 10.99 0.013
29.30 9.21
Discussion and Conclusions
Several significant relationships were revealed or suggested by the series of observations and
experiments reported here. While a number of these confirm earlier reports, others extend our
understanding of disease expression and of factors affecting disease incidence and severity.
Importance of Wounds
Sapstreak disease rarely occurs in nonwounded trees. Only a few cases were encountered while
observing disease occurrence in many sugarbushes and forests, and when such trees were excavated
they were found to be connected by functional root grafts to diseased trees that had been wounded.
Our studies (trial V) showed that root-graft transmission between closely adjacent trees can occur. But
the low level of its occurrence in our studies, and the relatively few times adjacent trees were observed
to become diseased in the field, suggest that this means of disease spread probably is not very common.
The nearly universal association of wounds and sapstreak disease is pivotal to the development of
control guidelines. The understanding gained in these studies, that the suitability of wounds as infection
courts depends on their type, their location on the tree, and possibly the season in which they are
inflicted, provides added information for development of management guidelines.
The general levels of "natural" disease incidence, especially of trees with initial symptoms, observed in
these studies was very low. Repeated observations revealed that for some sugarbushes, the disease is
occurring continuously, with a few new trees becoming symptomatic every year or so. In contrast, in
forest stands the majority of "new" trees often appears within a relatively short time span. This pattern
of occurrence probably reflects the infrequent but severe wound- inflicting disturbances related to
logging activities, and contrasts the less severe, but annual traffic-related disturbances in some
sugarbushes. In forest stands, sapstreak diseased trees usually exhibit initial symptoms 3-6 years after
the injury-causing event. While the period over which diseased trees die is frequently more protracted
in forest stands, the trees that are going to die will have done so within 6-8 years after having become
infected.
Which infected trees die and which do not is probably related to 1) the capacity of the tree to
compartmentalize injuries and limit the spread of infection, 2) the condition of the tree and its position
in the stand, and 3) the presence or absence of pathogens capable of attacking and killing weakened
root systems. Our studies and observations suggest that each of these factors is involved. Inoculation
Trials IV, V, and VI clearly showed that trees of approximately the same age, size, and vigor, inoculated
with equal amounts of the same isolate at the same time and by the same method, varied greatly in
their ability to resist or limit the spread of the pathogen. Indeed, some inoculated trees remained free of
infections altogether. Patterns of colonization, revealed through dissection, showed that trees usually
recovered if extensive spread and distribution of the fungus, particularly through the root system, had
not occurred within the first year or so after inoculation.
Importance of Root Disease Pathogens
Most naturally and artificially inoculated trees and saplings with root systems well colonized by C.
virescens died within 1 to 3 years after symptoms appeared. The nearly universal presence of Armillaria
sp. and Xylaria sp. (or both) fruiting bodies, mycelial fans, rhizomorphs or decay on trees that died, and
the absence of these organisms from sapstreak-infected trees that recovered suggests that their attack
is a major mortality-determining factor. These root fungi are ubiquitous inhabitants of long -established
northern hardwood forest stands. Successful invasion (at least for some Armillaria sp.) is governed by
stress factors or events that, by altering tree physiology, reduce resistance (Wargo and Shaw 1985). The
debilitating effect caused by extensive internal colonization of roots by C. virescens undoubtedly is a
significant stress. Other stresses, including defoliation and drought, also weaken and predispose roots to
infection. These factors, together with forest practices such as thinning, ensure a relatively continuous
supply of pathogen food bases.
The fact that significant mortality occurred soon after inoculation with C. virescens of saplings and polesize trees that had been severely defoliated earlier by gypsy moths probably reflects the influence of
defoliation, both as a predisposing factor to these root pathogens and as a factor contributing to the
buildup of their inoculum. That defoliation per se does not affect susceptibility to C. virescens was
shown by Trial III. The saplings in this stand had not been defoliated earlier and, by consequences of its
more recent origin, this stand did not harbor a significant load of root disease inoculum.
Conversely, some trees with severe sapstreak root infections also recovered. These were saplings and
trees whose position in the stand was favorable for growth and that also may have escaped attack by
root pathogens.
The opportunity to grow rapidly, to produce the energy required to establish barriers that restrict
infection, is dependent in large part on the amount of sunlight received. Saplings in the more open
stands, for example, Trial III and the sapling-sprouts of Trial 1, were able to limit infection and
subsequent mortality compared to those saplings in Trials I and II growing nearby in denser shade. The
sprouts also probably benefited from having an energy-producing, non-inoculated sprout member. And,
as discussed earlier, in addition to a better light regime, the saplings in Trial III and the sprouts in Trial I
also probably benefited from a somewhat lower root-pathogen inoculurn potential characteristic of
young forest stands established on recently abandoned open land.
Influence of Sap Collection Methods
Very low incidences of sapstreak were observed in sugarbushes; employing tubing collection systems
compared to bushes where sap is collected in buckets. Whether the abundant buttress root and root
injuries found in many "bucket" sugarbushes were the result of saphauling or of traffic at other times of
the year is not certain. When the disease did occur in tubing system sugarbushes, it was on injured trees
near sugarhouses, along logging skid trails, and in areas where cattle had trampled root systems.
Our studies examining the suitability of tapholes as infection courts (Trial VI) confirmed these
observations. Tapholes, regardless of their nature, were poor infection courts compared to buttress-root
bruises. Interestingly, however, the lengths of the discoloration columns (associated with all tapholes)
were greater about open (metal) than about closed (plastic with tubing) spouts, and tapholes made
early in the season had longer discoloration columns than those made later. The greater amount of
discoloration associated with metal spouts used in bucket collection systems is perhaps another factor
in favor of tubing systems.
Influence of Infection Courts Location
Injuries associated with sapstreak were almost always close to the ground. Even though stem tissues
were infected following their inoculation with large amounts of a grain-based inoculum (Trial IV), and
invasion of upper stems from infections originating in the roots or stem bases is common (Trial 1), no
cases were observed that suggested infection had occurred through broken branches or other wounds
of upper crowns or stems. Tapholes inoculated with conidial suspensions very rarely became infected
and when they did, the infections were strongly limited (Trial VI). In a number of cases, stump surfaces
created when one member of a sprout clump was removed in early summer thinning operations
appeared to be the avenue of infection for the residual stem. Such near-the-ground wounds comprise
especially suitable infection courts for C. virescens.
Influence of Season
Late spring to midsummer appears to be a critical period for sapstreak disease. The results of several
studies indicated that sugar maples are most susceptible to infection during this time (Trials I, II, and VI).
Mortality was highest in trees inoculated in late spring through mid-August. Late spring and early
summer is the period of greatest susceptibility of other tree species to similar vascular pathogens,
including elms (Dutch elm disease) and oaks (oak wilt). Not only are trees inherently more susceptible at
this time, this also is the period when heavy equipment used in the forest can create excessive rutting
and cause damage to roots and massive injuries to bark and wood of lower stems. And, finally,
temperatures and moisture conditions during this period usually are very favorable for rapid growth and
sporulation of C. virescens and for growth of the associated root pathogens as well.
Literature Cited
Beil, J. A.; Kessler, Jr., K. J. 1979. Sapstreak disease of sugar maple found in New York State. Plant
Disease Reporter. 63: 436.
Hepting, G. H. 1944. Sapstreak, a new killing disease of sugar maple. Phytopathology. 34:1069-1076.
Houston, D. R. 1985. Sapstreak of sugar maple: How serious is it? Maple Syrup Digest. 25(2): 24-27.
Houston, D. R. 1986. Sapstreak of sugar maple: appearance of lumber from diseased trees and longevity
of Ceratocystis coeruiescens in air-dried lumber. Phytopathology. 76: 653. Abstract.
Houston, D. R. 1991. Spread of the sugar maple sapstreak disease pathogen, Ceratocystis coerulescens,
via root grafts between Acer saccharum. Phytopathology. 81: 122. Abstract.
Houston, D. R. 1992. Importance of buttress root and taphole wounds as Infection courts for the sugar
maple (Acer saccharum) sapstreak pathogen, Ceratocystis coeruiescens. Phytopathology. 82: 244.
Abstract.
Houston, D. R.; Fisher, K. D. 1964. Sapstreak of sugar maple found In the northeast. Plant Disease
Reporter. 48: 788.
Houston, D. R.; Schneider, B. 1982. Sapstreak disease of sugar maple In N.Y. sugarbushes.
Phytopathology. 72: 262. Abstract.
Kessler, K., Jr. 1972. Sapstreak disease of sugar maple found In Wisconsin for the first time. Res. Note
NC-1 40. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment
Station. 2 p.
Kessler, K. J., Jr. 1978. How to control sapstreak disease of sugar maple. Information leaflet. St. Paul,
MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 5 p.
Kessler, K., Jr.; Anderson, R. L. 1960. Ceratocystis coeruiescens on sugar maple In the Lake States. Plant
Disease Reporter. 44: 348-350.
Ohman, J. H.; Kessler, Jr., K. J. 1963. Current status of the sapstreak disease of sugar maple In the Lake
States. Res. Note LS-1 0. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Lake States Forest
Experiment Station. 4 p.
Shigo, A. L. 1962. Observations on the succession of fungi on hardwood pulpwood bolts. Plant Disease
Reporter. 46: 379-380.
Shigo, A. L. 1977. Compartmentalization of decay in trees. Agric. Inf. Bull. No. 405. Washington, DC: U.S.
Department of Agriculture, Forest Service. 73 p.
Shigo, A. L. 1979. Tree decay: an expanded concept. Agric. Inf. Bull. No. 419. Washington, DC: U.S.
Department of Agriculture, Forest Service. 73 p.
Shigo, A. L.; Shigo, A. 1974. Detection of discoloration and decay In living trees and utility poles. Res.
Pap. NE294. Upper Darby, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest
Experiment Station. 11 P.
Shigo, A. L.; Shortie, W. C.; Garrett, P. W. 1977. Genetic control suggested In compartmentalization of
discolored wood associated with tree wounds. Forest Science. 23:179-182.
Smith, K. T. 1990. Sapstreak disease and biodeterioration of sugar maple. Biodeterioration Research. 3:
303-310.
Tattar, T. A.; Shigo, A. L.; Chase, T. 1972. Relationship between the degree of resistance to pulsed
electric current In wood In progressive stages of discoloration and decay In living trees. Canadian Journal
of Forest Research. 2: 236-243.
Wargo, P. M.; Shaw III, C. G. 1985. Armillaria root rot. The puzzle Is being solved. Plant Disease. 69: 826832.
Sapstreak Of Sugar Maple - How Serious Is It
Extension
Maple Syrup Digest
David R. Houston, USDA Forest Service Northeastern Forest Experiment Station 51 Mill Pond Road
Hamden, CT 06514
Vol. 25, No.2
July 1985
REF# 179
"One of my best running trees-sweet, too,--didn't run much sap at all year before last. In the spring, its
leaves were really small--sunlight came right on through it. This past summer it was dead."
"Over the years I've watched several trees near my sugarhouse die. Not many at a time--but probably
over a dozen, all told."
"Each summer I go through and cut down dead trees. I use them for fuel the next spring. There are
always one or two. Some haven't even been tapped yet. Sometimes the stumps have dark wood inside."
Do any of these descriptions by sugarbush operators in northern New York and Vermont sound familiar?
If so, it could be that sapstreak disease of sugar maple is present in your sugarbush. What is sapstreak?
How serious is it? Can it be prevented?
Cause
Sapstreak disease is caused by fungus Ceratocystis coerulescens. Ceratocystis is also the genus to which
the important pathogens of Dutch elm disease and oak wilt belong. It is also, however, the genus that
contains many nonpathogenic fungi, including those that cause blue-staining, especially of softwood
lumber. The fungus that causes sapstreak appears to wear two hats--it is a common stainer of hardwood
logs and lumber, but sometimes it enters living trees and turns killer. What triggers this "Jekyll to Hyde"
transformation is not clearly understood.
Symptoms
Usually, the first indication that a sugar maple tree has sapstreak is the thinning of its crown. The leaves
are small, often half or less the size of healthy ones (Fig. 1). In subsequent years, diseased trees may
show successive branch dieback and crowns may undergo a progressive deterioration.
Figure 1. The crown of sugar maples with sapstreak disease often appears thin because the leaves are
small. This “half-leaf “ symptom usually is the first indication that a tree has the disease.
Diseased trees sometimes succumb rapidly. Trees with no crown symptoms one year may fail to leaf out
the next, while others may die a year after the first foliar symptoms. By contrast, some trees linger for
many years, exhibiting repeated sequences of crown dieback and recovery until, finally, they die (Fig. 2a,
b).
Figure 2. Some affected sugar maples exhibit repeated sequences of dieback and recovery over several
years. This tree, which had small leaves over much of its crown in 1982 (a), exhibited extensive crown
dieback In 1983 (b).
Inside the tree, the wood of buttress roots and lower stems exhibits: a stain of distinctive color and
pattern. When freshly exposed, the stained tissue appears water-soaked and moist; it is yellowish-green
bordered by a thin, dark green margin (Fig. 3a). Imbedded in the stain are flecks that are reddish in color
when fresh. Within a few minutes of being exposed to air, the stain darkens dramatically and the red
flecks become less discernible. On drying, the discolored tissues fade to a light brown. In cross section,
the stain appears to radiate outward toward the bark in "finger-" or "star-like" projections (Fig. 3).
Cambium (the delicate growth layer between the bark and wood) touched by the stain dies and cankers
or dead areas develop. In severely diseased trees this radiating pattern disappears as the entire cross
section of roots becomes stained.
Figure 3. The distinctive stain pattern appears to radiate outward toward the bark In the lower trunk (a)
and in buttress roots (b) of diseased trees. Eventually, the entire cross section of the roots and stump
become discolored.
As sapstreak continues to develop, the flow of sap begins to slow and finally ceases. This reduction in
flow can occur even before crown symptoms appear. In such cases, it is likely that the taphole was
placed in diseased wood. As evidence, drill shavings from such wood will be moist, often "mealy" in
consistency, and discolored compared to bright, crisp shavings from healthy wood.
Wound Association
Wounds appear to be positively associated with sapstreak disease. At some time in its life, nearly every
infected tree has been wounded severely on its roots or buttress-root area. Because this wounding may
occur many years before symptoms develop, wounds are sometimes nearly closed by callus (new wood)
by the time the disease is recognized. The close association of wounds and disease seems related to
where diseased trees are located in the sugarbush or forest.
Location of Diseased Trees
Trees affected by sapstreak are found primarily along skid trails in the forest or along haul roads in a
sugarbush. The more heavily used the roadway, the more likely it is that adjacent trees will be wounded
when logs are skidded or wood and/or sap is hauled. Thus far, significantly more diseased trees have
been found in sugarbushes where buckets are used than in those where tubing is used, presumably
because of the greater number of injuries inflicted during the many trips through the sugarbush to
gather sap.
Although diseased trees often occur as scattered individuals, there are instances where they occur in
groups. In several sugarbushes, concentration of diseased trees have been found near the sugarhouse
(Fig. 4). In some sugarbushes and forest areas, groups of diseased trees also seem to occur in poorly
drained areas where soils are wetter than normal.
Figure 4. This map of a sugarbush in upstate New York shows the locations of the sugarhouse and the
surrounding trees, and illustrates how sapstreak progressed between 1980 and 1983. Note that the
diseased trees were located where they were especially subject to wounding.
Factors Affecting Spread And Development Of Sapstreak
Although there is a strong correlation between buttress-root wounds and disease occurrence, many
unanswered questions remain. Knowing the answers to these questions is important if we are to
understand the disease and its prevention. For example, we do not know whether other wounds such as
broken branches, insect injuries, or even tapholes can serve as places for infection to start. Is the
observed greater incidence of disease in bushes where buckets are used due to more traffic-caused root
injuries? Or could "open" spouts be more accessible to the fungus than "closed" tubing systems? Where
does the fungus reside and what role does it play outside of diseased trees, and how does it get from
one tree to another? Insects are suspected as the primary vectors, but which ones? And can the fungus
move through root grafts, or be spread on tools such as drill bits, saws, or axes?
The occurrence of diseased trees in groups could be the result of (a) local transmission through common
root grafts or through dissemination by vectors with limited territories; (b) the infliction of injuries to
groups of trees at specific times; or (c) concentration of the causal fungus. Concentrations of dying or
dead trees also could result from interactions with other pathogens, such as those causing root rots.
Nearly all trees killed by sapstreak also are severely attacked by one or more root fungi, some of which
are known to attack and kill groups of stressed trees,
Is sapstreak a serious malady? We are not sure. We do know through inoculation trials that C.
coerulescens is a virulent pathogen --sometimes able to kill saplings in a few weeks, and trees in a few
months. Yet in nature, the disease thus far has occurred only sporadically and relatively few trees have
been affected. While this may reflect, in part, our past inability to recognize the disease, it probably also
attests to the fact that a specific set of conditions must be met before the interactions required for the
disease occur. Only when we more fully understand how the fungus moves through the sugarbush and
infects trees, and the factors that cause some trees to be infected while hundreds of others--even when
severely wounded--are not affected, will we know if sapstreak has the potential to cause a disaster in
the sugarbush--or if it will continue to remain a scattered problem.
Acknowledgments
I thank personnel of the New York State Department of Environmental Conservation for their continuing
assistance in our studies of sapstreak. I also thank the several landowners who have made their
sugarbushes available for our research.
Additional Reading
Hepting, G.H. 1944. Sapstreak, a new killing disease of sugar maple. Phytopathology 34:1069-1076.
Houston, D. R., and K. D. Fisher. 1964. Sapstreak disease of sugar maple found in the Northeast. Plant
Dis. Rep. 48:788.
Houston, D.R. and B.S. Schneider. 1982. Sapstreak disease of sugar maple in N.Y. sugarbushes. (Abstr.)
Phytopathology 72(2):262.
Kessler, K.J., Jr., and R.L. Anderson. 1960. Ceratocystis coerulescens on sugar maple in the Lake States.
Plant Dis. Rep. 44:348-350.
Kessler, K.J., Jr. 1978. How to control sapstreak disease of sugar maple. Available from Northeastern
Area, State and Private Forestry, 370 Reed Road, Broomall, PA 19008, or North Central Forest
Experiment Station, 1992 Folwell Ave., St. Paul, MN 55108.
Wound Closure In Sugar Maple Adverse Effects Of Defoliation
Research
United States Department of Agriculture
Philip M. Wargo
Northeastern Forest Experiment Station, Forest Service, Hamden CT, U.S.A. 06514
Can. J. For. Res. 7: 410-414.
March 1, 1977
REF# 017
Abstract
Twenty-three sugar maple trees, Acer saccharum Marsh., that had been defoliated by hand for 3
consecutive years (1971, 1972, and 1973) and nine undefoliated trees were wounded with a drill bit in
March 1974. After two full growing seasons, wound areas on defoliated trees were larger than those on
undefoliated trees because more bark tissue died originally around the wounds on defoliated trees, and
because there was less wound closure resulting from poorer radial growth. There was no significant
increase in internal discoloration, but decay was found in two defoliated trees. In undefoliated trees,
wound area was highly correlated with annual growth increment and resistance to pulsed electric
current. In defoliated trees. wound area was highly correlated with starch content of the roots; trees
with lower starch content had larger wounds.
Vingt-trois érables à sucre, Acer saccharum Marsh., défoliés à la main pendant 3 années consécutives
(1971, 1972 et 1973) et neuf autres érables servant de témoins furent blessés avec un foret on mars
1974. Après deux saisons complètes de croissance, la zone affectée par les blessures était plus grande
chez les arbres défoliés que chez les témoins. Cette difference était due d'une part à une nécrose plus
prononcée de l'écorce au tout début et, d'autre part, à la fermeture moins rapide des blessures à cause
d'une croissance radiale plus faible chez les arbres défoliés. Il n'avait pas d'augmentation significative de
la coloration du bois à l'intérieur, mais par contre la carie fut détectée dans deux des arbres défoliés.
Dans le cas des arbres témoins, l'étendue de la zone affectée par les blessures était étroitement reliée
au taux de croissance annuel et à la résistance à un courant électrique pulsé. Chez les arbres défoliés la
superficie de la zone affectée par les blessures était en relation étroite avec le contenu on amidon des
racines; plus le contenu en amidon était faible, plus la zone affectée par les blessures était grande.
[Traduit par le journal]
Introduction
The relationship of defoliation to tree mortality has been well documented (Staley 1965; Nichols 1968;
Campbell and Valentine 1972; Kegg 1973), but less obvious effects of defoliation on tree vigor can also
have significant impact on forest stands. Tree vigor affects the response by trees to wounding (Swarbrick
1926; Neely 1970L and defoliation may impair a tree's ability to close a wound and compartmentalize
the affected tissues (Shigo and Hillis 1973).
Material and Methods
Sugar maple saplings that were 15 to 18 years old and 3 to 8 cm in diameter at 1.4 m aboveground in
1974 had been defoliated by hand in May, June, July, or August in 1971, 1972, and 1973. However, only
seven tree, that were defoliated (100%) in May, two Mat were defoliated in June, seven that were
defoliated in July, and nine that were defoliated in August survived for wounding. In early March 1974
the trees were wounded with a 10 mm drill bin a single hole was bored 2.5 to 3.0 cm deep at 0. 15 m
aboveground. Nine undefoliated trees also were wounded in 1974. The trees were cut and examined in
November 1975, after two full growing seasons. The two trees in the June group that survived
defoliation died during the 1974 growing season and were excluded from my study.
The size of the wound was determined by measuring the length and width of the exposed discolored
wood between the calloused edges (see Fig. 1) at the longest and widest points, the wound area was
calculated for an ellipse. The bolts were then split and the extent of discoloration in the wood above and
below the wound was measured. Also measured was the extent of discoloration (above and below the
wound) in the last annual ring that was present at the time of wounding. The annual radial increment
after wounding (1974 and 1975) was measured near the wound site. Decay, if present, was noted but no
attempt was made to isolate organisms from the tissues.
Figure 1. Dead tissue (discolored) around wound holes in stem sections of defoliated (1971, 1972, and
1973) and undefoliated sugar maple two full growing seasons after wounding in March 1974. Top left.
defoliated in May. Top right, defoliated in July; bottom left, defoliated in August; bottom right,
undefoliated.
The starch content of the roots of these trees was estimated from starch measured in one root in the
autumn of 1973, 1974, and 1975 (Wargo 1975); the resistance of the stem tissue at 1.4 m to pulsed
electric current was measured every 2 weeks in 1974 and weekly in 1975 with a Shigometer model 7950
by inserting uninsulated stainless-steel electrodes through the intact bark into the wood (Wargo and
Skutt 1975). In analyzing the data, the natural logarithm of the wound area was used as the dependent
(y) variable to ensure homogeneity of the variance, the assumption on which the analysis was based.
Results
The average wound area was larger on defoliated trees (Table 1 ). Duncan's multiple range test was
applied to the data; results indicated that the average wound area on undefoliated trees was smaller
than the wound area on trees that were defoliated in May and July (P < 0.01 ), and smaller than the
wound area on trees defoliated in August (P < 0.05). Differences in wound area among, the defoliated
trees were not statistically significant. The average wound area was much larger for trees that were
defoliated in May and July than it was for trees defoliated in August, but unusually large wounds on two
trees in the May group and two in the July group accounted for the differences.
Table 1. Average wound area, radial increment, root starch content, and resistance to pulsed electric
current (ER), and standard errors, for defoliated (1971, 1972, and 1973) and undefoliated sugar maple
tree % two full growing seasons after wounding in March 1974
Year of Defoliation treatment
Item
measurement May
July
August Undefoliated
Wound area, cm
1975
18.2 ± 10.0
27.5 ± 16.0
3.5 ± 1.2
0.7 ± 0.2
Radial increment, cm
1974
0.03 ± 0.03
0.05 ± 0.02
0.10 ± 0.05
0.28 ± 0.07
0.09 ± 0.03
0.15 ± 0.06
0.25 ± 0.07
1975
0.08 ± 0.03
Root starch, % dry weight
1973
5.30 ± 2.30
2.70 ± 1.40
3.60 ± 1.20
1974
9.40 ± 2.90
2.00 ± 0.90
5.10 ± 2.20
9.10 ± 1.00
1975
8.10 ± 1.80
3.60 ± 1.70
6.20 ± 2.50
8.10 ± 0.80
9.30 ± 1.30
ER, kW 1974
38 ± 4 41 ± 6 36 ± 5 24 ± 4
1975
32 ± 3 31 ± 4 28 ± 4 20 ± 3
The differences in wound area between defoliated and undefoliated trees resulted from the response of
tissues to wounding. More tissue died originally around the wound on defoliated trees, resulting in
larger initial wounds (Fig. 1).
The wound had closed (no exposed wood) on only 1 of the 23 trees that were defoliated, and that was a
tree from the August group; trees in this group seemed to be less severely affected by defoliation (Table
1); the wounds on 3 of the 9 undefoliated trees had completely closed (Fig. 1, bottom, right).
Wound closure was strongly related to tree vigor. All measurements indicated that the undefoliated
trees were more vigorous; they had higher radial increment, more root starch, and a lower resistance to
pulsed electric current (ER) than the defoliated trees (Table 1).
Among undefoliated trees, those with higher radial increment and a lower ER had the smallest wounds.
Wound area had a high negative correlation with growth increment and a high positive correlation with
ER, especially for the 1975 measurements (Table 2). However wound area was not highly correlated
with root starch (Table 2). The highest multiple correlations for wound area among undefoliated trees
occurred when data for radial increment (R = - 0.95) or ER (R = +0.98) for both 1974 and 1975 were
combined; radial increment and ER for 1975 were also highly correlated (R = -0.91).
Table 2. Correlations between log wound area and radial increment, log resistance to pulsed electric
current (log ER), and log root starch content, on defoliated and undefoliated sugar maple trees.
Defoliation treatment
Year of May
July
August Undefoliated
Tree vigor indexmeasurement (7)a
(7)a
(9)a
(9)a
Radial increment
-0.28
-0.68
-0.78
-0.87
--0.60 --0.61 -0.83
-004
-10.57 +0.76 UK
+0.62
1975
Log ER 1974
1975
-10.54 -10.87 +0.74 +0.90
Log root starch 1973
1974
1974
-0.65
--0.87 -0.88
-0.43
-0.75
-O.03
+0.30
1975
--0.55 -0.87
-0.66
-0.17
aObservations per treatment in parentheses.
Among defoliated trees, correlations between wound area and radial increment, and between wound
area and ER were different for each defoliation treatment, and were usually lower than those for
undefoliated trees (Table 2). But, the relationship between higher radial increment and lower ER and
smaller wound area observed in the undefoliated trees was the same. Correlations were also higher for
the 1975 measurements. In contrast with undefoliated trees, there was a high negative correlation
between wound area and starch content that was measured in 1974 for all defoliated trees and that
measured in 1975 for trees defoliated in July (Table 2).
Although all trees were initially of similar diameters the defoliated trees were substantially smaller than
the undefoliated trees at the time of wounding (May, 3.25 ± 0.17 cm; July, 3.35 ± 0.12; August, 4.19 ±
0.34; undefoliated, 4.98 ± 0.37). However correlations between wound area and diameter were not very
high (all trees, R= -0.74; defoliated, R= -0.59; undefoliated, R = -0.69).
There were no significant differences in the extent of internal discoloration among the groups that
received different treatments, either in the maximum extension above or below the wound in the total
wood or in the last annual ring present at the time of wounding. However a bleached zone in the wood
near the wound hole occurred more frequently among defoliated trees and was larger (area) in the
defoliated trees. In addition, two trees had decay established in the wood and both were defoliated
trees, one from the May group and the other from the July group.
Discussion
Defoliation by phytophagous insects increases mortality (Stephens 1971 ) and reduces growth (Kulman
1971 ). This study shows that another significant effect of defoliation is to delay wound closure; the
effect of wounding is more severe, resulting in larger wounds, and closure is slower because radial
growth is reduced. Discoloration and decay that result from delayed wound closure may cause increases
in internal defect and economic losses. Thus tree damage may be greater from thinning operations,
increment coring, or other activities that may wound trees that have been or are being defoliated.
These results would have a direct effect on the maple syrup industry; tap hole drilling on defoliated
trees would result in larger wounds around the tap hole and possible decay. The dieback of tissue
around the original wound and the internal bleached zone that was observed near the wound on
defoliated trees are similar to those that were observed when paraformaldehyde pills were inserted in
tap holes to prevent clogging, but which resulted in early establishment of decay (Shigo and Laing,
1970).
The trees that were selected for my study had been defoliated for 3 consecutive years, so we can only
speculate on whether the effects of wounding would have been less severe on trees defoliated for only
1 or 2 consecutive years. Carbohydrate reserves can be depicted in some trees after only 1 year of
defoliation (Wargo et al. 1972), and on some trees the effects of wounding could be adverse after only 1
year of defoliation. The strong negative correlation between wound area and starch content suggests
that wounding when trees have low or depleted food reserves will produce larger wounds, regardless of
how many years it took to deplete the reserve.
Among the defoliated trees, the poor correlation between wound area and radial increment probably
resulted from poor radial growth and initial effects of wounding. Among defoliated trees, wounds were
actually larger because of bark dieback around the drill hole, and not all wounds were the same size
when healing began. Wound width and annual radial increment significantly influence the rate of
healing (Neely 1970). Since the wounds in undefoliated trees were initially about the same size, there
was good correlation between wound closure and radial increment.
In a previous experiment, Wargo and Skutt (1975) found that tree vigor, as indicated by crown class and
crown condition, and stress from defoliation by the gypsy moth, were reflected in resistance to pulsed
electric current. The high positive correlation between wound area and resistance to pulsed current is
another indication that tree vigor is reflected in ER. It was easier to measure than radial increment, and
it was a better indicator of tree vigor (according to wound closure) than diameter.
Acknowledgments
I thank Dr. Alex L. Shigo for technical advice; Roy L. Patton, Chris Fagan, Barbara Schultz, and Michael
Boutin for technical assistance; and the New Haven (Connecticut) Water Co. for its cooperation and the
use of its forests.
Literature Cited
Campbell, R. W., And H. T. Valentine. 1972. Tree condition and mortality following defoliation by Gypsy
Moth. U.S. For. Serv. Res. Pap. NE-236.
Kegg. J. D. 1973. Oak mortality caused by repeated gypsy moth defoliations in New Jersey. J. Econ.
Entomol. 66: 639-641.
Kulman, H. M. 1971. Effects of defoliation on growth and mortality of trees. Annu. Rev. Entomol. 16:
289- 324.
Neely, D. 1970. Healing of wounds on trees. Am. Soc. Hortic. Sci. 95(2): 536-540.
Nichols, J. 0. 1968. Oak mortality in Pennsylvania: a ten- year study. J. For. 66: 681-694.
Shigo, A. L., And W. E. Hillis. 1973. Heartwood, discolored wood, and microorganisms in living trees.
Annu. Rev. Phytopathol. 11: 197-222.
Shigo, A. L., And F. M. Laing. 1970. Some effects of paraformaldehyde on wood surrounding tapholes in
sugar maple trees. U.S. For. Serv. Res. Pap. NE161.
Staley, J. M. 1965. Decline and mortality of red and scarlet oak. For. Sci. 11: 2-17.
Stephens, G. R. 1971. The relation of insect defoliation to mortality in Connecticut forests. Conn. Agric.
Exp. Stn. New Haven. Bull. 723.
Swarbrick, T. 1926. The healing of wounds in woody tissue. 1. Pomol. Hortic. Sci. 5: 98-114.
Vargo, P. M. 1975. Estimating starch content in roots of deciduous trees-a visual technique. U.S. For.
Serv. Res. Pap. NE-313.
Vargo, P. M., 1. Parker, And D. R. Houston. 1972. Starch content in roots of defoliated sugar maple. For.
Sci. 18: 203-204.
Wargo, P. M., And H. R. Skutt. 1975. Resistance to pulsed electric current: an indicator of stress in forest
trees. Can. J. For. Res. 5: 557-561.
Stress Triggered Tree Diseases - The Diebacks and Declines
Extension
United States Department of Agriculture
David R. Houston, Principal Plant Pathologist
Forest Service, Northeastern Forest Experiment Station, Hamden, Connecticut, NF-INF-41-81,
Watercolor illustrations by David M. Carroll Warner, New Hampshire.
1981
REF# 019
Foreword
Traditionally, dieback and decline diseases of trees have been described in generalities, attributed to
unknown or mysterious causes, and thought to be beyond the scope of human intervention. This
publication provides a basis for understanding and coping with these diseases. Discussed are concepts
relating to: (1) diagnosing the factors that initiate the disease; (2) describing symptoms and disease
development; (3) determining the role of secondary-action organisms; and (4) developing appropriate
control measures.
The concepts presented here are drawn from more than 15 years of research on diebacks and declines
conducted by the author and by his colleagues, Drs. Johnson Parker and Philip M. Wargo. Dr. Wargo's
research on the relationship of stress-induced changes in trees and susceptibility to microorganisms has
especially contributed to our understanding of these complex diseases.
Introduction
Diebacks and declines are complex diseases and, while they differ from each other in specific details,
they share certain relationships of cause and effect. Each is initiated by an adverse environmental
factor. Stress and each is culminated by often lethal attacks by organisms that are otherwise
insignificant. As their condition worsens, affected trees show common symptom patterns; that is, they
dieback, decline, and ultimately may die. A general framework for the dieback-decline diseases is shown
in Figure 1.
Figure 1. A conceptual framework for the dieback- decline diseases. Healthy trees are affected by
environmental stress; over time, trees altered by that stress are invaded at some point by secondaryaction organisms. The disease condition develops and trees dieback, decline, and ultimately may die.
The dieback and decline disease can be expressed by the following word equations:
These equations imply that when the stress abates, and in the absence of lethal attacks by secondary
organisms, trees can recover over a period of time or growing seasons.
In recent decades, dieback and decline diseases have killed or damaged millions of trees in the
northeastern United States. Most hardwood tree species probably have been affected by dieback and
decline diseases at some point, but relatively few species have suffered greatly. Unfortunately, the
species affected most severely are among the most important ones. And the incidence and severity of
these diseases seems on the rise. In this publication, special emphasis is placed on the decline and
mortality of oak initiated by gypsy moth defoliation. The significant impact of this widespread
defoliation in recent years has prompted great concern and considerable research.
Important Diebacks and Declines: Nature, Causes, and General Relationships
Ash Dieback
Dieback of white ash, and occasionally of green ash (Fig. 2), is typical of dieback and decline diseases. It
is initiated by the stress of water shortage. Especially severe outbreaks were associated with periods of
low rainfall in the 1930's and more recently from 1950 to the early 1960's.
Figure 2. Dieback of ash begins when water shortages (1) alter the bark of healthy ash trees (2) and
predispose it to attack by fungi (3) that cause cankers on branches and stems (4). The condition worsens
over time and affected trees may continue to dieback (5), decline (6), and die (7)-even after the stress
has abated and water tables have been restored (8).
The onset of ash dieback is signaled by the reduced growth of stems and twigs. This is followed
successively by the death of terminal buds and branches and by the production, often at nodes, of small,
sparse and chlorotic leaves. Affected crowns appear thin and tufted.
On some trees, leaves prematurely acquire the characteristic purple-bronze color of autumn and drop
early. As trees progressively die back, in toward the trunk and down toward the ground, bole sprouts
often develop. Finally, the trees die.
Soon after the onset of symptoms, reddishbrown to orange-yellow cankers develop on the branches and
on smooth bark of the main stem. When these cankers girdle twigs or stems, they contribute markedly
to the dieback process. At least two canker fungi, Cytophoma pruinosa and a Fusicoccum species, attack
bark tissues made susceptible by water shortages. These fungi, common inhabitants of bark of shaded,
lower crown branches, are thought to contribute under normal conditions to the death and “selfpruning” of lower branches so characteristic of forest-growth ash trees.
Ash dieback, as shown in Figure 2, can be thought of as a "system" whose word equations can be stated:
Other factors may be involved in ash dieback. Ash trees are hosts for viruses and mycoplasmas, and they
are highly susceptible to injury from air pollution. How much these factors may contribute to ash
dieback is uncertain; it may be significant that while the abatement of the disease generally has
coincided with abatement of drought periods, the dieback and decline of ash has continued in some
areas where there are viruses, mycoplasmas, and high levels of air pollution.
Beech Bark Disease
The environmental stress factors that predispose trees to attack by secondary organisms can be abiotic,
such as the water shortage associated with ash dieback, or they can be biotic. Such is the case with
beech bark disease (Fig. 3).
Figure 3. Beech bark disease occurs when bark tissues, altered by the feeding of the beech scale
Cryptococcus fagisuga (1), are invaded and killed by a canker fungus, Nectria coccinea var. faginata (2).
Heavily infested trees often appear whitewashed from the "wooly" wax secreted by the insect (3). As
the disease progresses, the tree crown can become thin and chlorotic (4). Infection by Nectria is signaled
by the appearance of dark, weeping exudates on the bark (5), and by red fruit bodies (6). Trees may
snap off when wood beneath killed bark tissues becomes decayed (7). Eventually, in the aftermath of
heavy mortality, a thicket forest of root sprouts may develop that is highly defective (8). Occasionally, an
apparently resistant tree can be found (9).
Beech bark disease is initiated when the beech scale (Cryptococcus fagisuga), a tiny, wingless insect,
feeds on the bark of beech trees. The white, "wooly" wax secreted by the insect as it feeds is the first
evidence of the disease. Heavily infested trees may appear whitewashed.
Since its accidental introduction to Nova Scotia shortly before the turn of the century, the beech scale
has spread slowly south and west. It now is found as far south as east-central Pennsylvania, and as far
west as western New York.
As with other diebacks and declines, the effects of the stress agent alone usually are not sufficient to kill
trees. The massive tree mortality that follows shortly after a buildup of beech scale results from the
invasion of scale-altered bark by another organism, in this case, the canker fungus, Nectria coccinea var.
faginata. Early signs of infection include a dark, weeping exudate known as a tarry spot or slime flux.
Later, white sporodochia with long cylindrical spores (the asexual stage) and especially red perithecia
with ascospores borne in asci (the sexual stage) often develop in great abundance in areas of bark
previously inhabited by the beech scale. The presence of the fungus fruiting bodies is sure evidence that
bark tissues have been killed. Often, bark tissues are killed in local patches and the wood beneath
becomes invaded by wood borers and decay fungi. Trees may break off at these points-a condition
known as beech snap.
The beech bark disease system, therefore, can be expressed by the equations:
In many forests where large numbers of old, mature trees were either cut or killed by the disease, dense
thickets of young beech trees have developed from root suckers. Often, these emerging stands are
heavily infested by another insect, Xylococculus betulae. Small, young beech trees usually are quite
resistant to C. fagisuga, but erumpent wounds created by Xylococculus provide places on these young
stems for the beech scale and, subsequently, for Nectria.
In areas where the disease is widespread, there may be trees that are free of signs of the beech scale
insect or Nectria fungus. This offers hope that resistance to the disease may occur in nature.
Maple Declines
Several different diebacks and declines of sugar maple have been recognized. Figures 4-7 depict these
diseases affecting trees growing along a roadside, in a sugar bush and in the forest.
Figure 4. Declines of sugar maple occur in the forest (left), in the sugarbush (center), and along highways
(right).
Roadside maples
The decline of sugar maple along roadsides (Fig. 5) occurs when trees are subjected to the effects of
road salting in winter or are affected by water shortages associated with drought or road paving. Many
of the declining roadside trees were planted a century or more ago and are now overmature. Often, the
root system of these trees, encroached upon when roads were widened and later paved, loses its ability
to meet the growing trees' demands for moisture. Injured and weakened roots provide avenues for
entrance for many organisms-and often set the stage for decay and deterioration.
Figure 5. Along roadsides, trees are stressed by drought, road paving, and especially by deicing salt. As
trees decline, their weakened and killed tissues often are invaded by a host of organisms including decay
fungi.
Sugar maple is especially sensitive to both sodium and chloride ions of deicing salt. The greatly increased
use of this chemical in recent years has hastened the decline of many trees already struggling for
survival in the roadside environment. Deteriorating trees, whose thin crowns support sparse clumps of
small leaves that often prematurely exhibit fall coloration, and rows of stumps bordering roadsides of
the Northeast testify to the magnitude of this problem.
Sugarbush maples
In recent years, many old sugar maple trees have declined and died in sugarbushes of the Northeast.
While the reasons for this are not thoroughly understood, the decline has been most severe in
sugarbushes that have been subjected to drought, heavy grazing, or over-tapping and heavy traffic by
farm machinery used in the sap gathering process. Many of the seriously affected trees are overmature
and have been heavily tapped for many years. These trees usually are riddled with decay associated with
tapholes and root wounds made by cattle or machinery. Decline in these sugarbushes often is
accelerated by insect defoliation. Studies have shown that wounds such as tapholes are not closed over
as rapidly by trees that have been defoliated; coupled with drought, damaged roots, and overtapping,
the effects of defoliation can be devastating. In fact, defoliation itself is a primary factor that initiates
maple decline, and it has been especially serious in some forest environments.
Figure 6. Decay fungi complete the decline of maples growing in the sugarbush. Here, the major
stresses of overtapping and of injuries to roots made by cattle and machinery weaken trees, making
them susceptible to attack by organisms that break down woody tissues.
Forest maples
Maple decline in the forest often occurs after defoliation by a number of insects including leafrollers and
webworms, the saddled prominent, and the forest tent caterpillar. Declining trees are marked by
terminal dieback, progressive deterioration of the crowns inward and downward, and the production of
"clumps" of foliage on sprouts. Death of weakened twigs can be hastened by attacks by weakly
pathogenic fungi such as Steganosporum ovatum, and root systems of defoliated trees often are rapidly
invaded and killed by the shoestring root rot fungus, Armillaria mellea.
Defoliation-initiated maple decline can be expressed by the equations:
The relationship between defoliation and attack by organisms such as A. mellea is discussed in greater
detail in sections on oak decline and mortality after defoliation by the gypsy moth.
Figure 7. Defoliation (1) is the major stress factor in the decline of forest maples. Severely defoliated
trees suffer marked branch dieback, and are susceptible to attack by several organisms including twig
fungi (2) and A. mellea, the shoestring root rot fungus (3).
Reducing or Preventing Diebacks and Declines: General Concepts
The unique relationships of cause and effect and patterns of distribution discussed previously must be
considered when attempting to control or prevent dieback and decline diseases. Control measures for
diseases caused by primary, highly pathogenic organisms usually are directed against the pathogen
itself. But control measures for dieback and declines usually focus on reducing or preventing the
predisposing stress factor.
These relationships affect the approach taken by both pathologists and plant breeders to control these
diseases. Thus, pathologists are more concerned with discovering why trees have suddenly become
susceptible to attack by organisms of secondary action and with the "spread" and intensification of
initiating stress factors, than with classical studies of reproduction, buildup, and dispersal of the
organisms themselves. Likewise, plant breeders are not as concerned with developing resistance to
secondary-action organisms directly as with developing resistance to the factors that predispose the
trees to those organisms.
Forest and Woodlot
Some of the ways that diebacks and declines can be reduced in the forest and in urban areas are
illustrated in Figures 8 and 9. When the stress factors are biotic, direct actions such as spraying can
reduce or prevent the effects of severe infestations by sucking or defoliating insects. But the control of
abiotic stress factors may be more difficult. In the forest, thinning to remove weak or dying trees
reduces competition for moisture and nutrients; and encouraging species best adapted to the site may
help minimize the effects of stresses such as drought and frost. In some situations, converting from one
forest type to another that is better suited to the site- perhaps by clearing and planting may be the most
appropriate solution. Reducing the number of logging wounds and associated decay will enable trees to
better tolerate effects of added stress.
Figure 8. Ways to reduce diebacks and declines in the forest include timber stand improvement to
remove defective, weak, or dying trees, and thinnings to reduce competition (stress) for moisture and
nutrients and to favor species best suited to the site (1); converting one forest type to another better
suited to the site (2); controlling outbreaks of defoliating insects when necessary or feasible (3); and
reducing the number of wounds from careless logging or overtapping (4).
Figure 9. Ways to prevent or reduce diebacks and declines in urban areas include watering (1) and
fertilizing (2); covering tree root zones (3) and walkways with organic residues to alleviate water
shortages and soil compaction; planting new trees (4) to avoid roadside stresses (5); pruning weak and
dead branches to promote rapid closure and discourage decay (6); and spraying when necessary and
feasible to control insects such as scales (7) and defoliators (8).
In the sugarbush, actions should be directed toward keeping trees as healthy as possible and toward
reducing the adverse effects of wounds from cattle trampling, and from excessive tapping and other
activities associated with producing maple sugar. Overtapping in general and probably any tapping the
season following a severe defoliation should be avoided.
Urban Environments
It is often possible to do more to alleviate the effects of stress in urban areas (Fig. 9) than in the forest.
Moisture shortages can be prevented or alleviated by watering and fertilizing, by reducing competition
from sod by placing mulch over the root zones of yard trees, and by avoiding soil compaction by
covering walkways with wood chips or other organic mulches. Timely and judicious pruning of tree
crowns will help trees in times of moisture stress, and removing weak or dead branches will help
promote rapid wound closure and reduce the chance of decay. Planting new trees away from roadsides
will avoid many severe stresses of the urban environment. Spraying to control sucking and defoliating
insects when necessary and feasible will help prevent dieback and decline diseases of specimen trees.
Since diebacks and declines are initiated by stress and disturbance, it can only be concluded that these
diseases will continue to proliferate as the number and diversity of stress factors increase with
expanding urbanization.
The foregoing sections describe the general nature of dieback and decline diseases and the ways to
reduce their significance. In the following sections, oak decline and mortality, a dieback decline that has
followed the widespread outbreaks of gypsy moth in the Northeast, is examined in detail.
Oak Decline and Mortality Initiated by Gypsy Moth Defoliation: A Case Study
The Process of Oak Decline
Diebacks and declines of oaks are not new to forests of the East. Numerous instances of severe
problems have been associated with stress factors such as late spring frost, drought, and insect
defoliation, singly and in concert. In recent years, severe defoliation by gypsy moths in New England,
New York, New Jersey, and Pennsylvania has triggered the decline and death of millions of oaks (Fig. 10).
Regardless of the predisposing factors involved, the death of trees is primarily associated with the lethal
attacks by Armillaria mellea, by Agrilus bilineatus, the twolined chestnut borer, or both.
Figure 10. Oak decline occurs when healthy oaks (1), predisposed by the effects of defoliation by insects
such as the gypsy moth (2), frost (3), or drought (4) are attacked and killed by the shoestring fungus,
Armillaria mellea (5) and the twolined chestnut borer, Agrilus bilineatus (6). Trees on ridge tops and in
wet areas suffer most severely from drought, and frost often affects trees growing in valleys and frost
pockets (center background). Trees defoliated sufficiently to be refoliated the same season (center
foreground) may show symptoms the next year (7). Repeated defoliations can result in tree death as
weakened trees succumb, sometimes suddenly, (8) to the girdling actions of the borer above ground,
and of the fungus below.
We can describe the system of defoliation initiated oak decline by these equations:
In the following sections we will examine how defoliation affects trees, and how these effects render
them susceptible to attack by A. mellea and A. bilineatus.
The Defoliation Stress
The function of leaves is to convert sunlight energy into chemical food energy needed by the tree for
maintenance, growth, and reproduction. Defoliation, therefore, adversely affects the tree by interfering
with its energy regimen. Fewer leaves mean less food produced and less growth. While this direct
relationship exists for any level of defoliation, low levels usually are not harmful aside from reducing
radial and terminal growth. But the removal of 50 to 60 percent or more of a tree's leaves can be very
serious because such levels trigger major responses by the tree that can be deleterious to its function or
form.
Refoliation-Dieback: Responses of Individual Trees to Defoliation and Their Consequences
Severe defoliation can cause trees to refoliate, an event that places them in an "out of phase" condition
with respect to the growing season (Fig. 11). Buds formed for the next year are forced to break one
season too soon, and the new leaves must produce food and new buds in a shortened growing season.
Sometimes new leaves are immature when fall arrives and new buds have not been formed. Even when
defoliation occurs early enough in the season for the new foliage to grow and mature, the new small
terminal buds may not be winter hardy. When the terminal buds are killed or injured, or do not have
time to form, twigs die back to the point where there are sound lateral buds.
Figure 11. Crown symptoms and root starch content (food energy reserves) in a nondefoliated oak tree
(green track, left) compared with a defoliated tree (red track, right) over two growing seasons. Severe
gypsy moth defoliation in June triggers refoliation. Food reserves stored as starch in roots (dark color of
cross sections) are converted to sugars to provide energy needed until there are new leaves. New leaves
produce insufficient food to replace that used, and trees enter the next winter with low or depleted
starch reserves. Branch dieback may result from winter desiccation of buds, and from lack of food
reserves; in the season after defoliation, leaves often are small, off color, and "clumped." A second
defoliation further depletes starch reserves, the decline continues, and the trees may die. If defoliation
is not repeated and growing conditions are favorable, the trees may recover (green track, right).
Adverse changes are also occurring inside the tree. Sugars produced by the leaves usually are moved to
the roots where they are stored as starch food reserves. Normally, food reserves are highest in the fall
after a full summer's production. But defoliation and refoliation can change all of this. When buds break
and leaves start to grow, starch is converted to sugars and sent to the growing areas to maintain the
tree until there is new foliage. Often, tree roots are completely depleted of their starch by this process
and little is replaced before the end of the growing season.
The effects of defoliation are most serious when it occurs just after "normal" leaves are produced in late
spring-early summer but before starch reserves have been replenished. With such low food supplies, the
energy demands of all the branch and root tissues cannot be met until new leaves are formed and some
tissues die back.
The dieback process, which may be repeated again and again as the defoliation stress continues, serves
as a survival mechanism. By reducing the amount of energy-requiring branch and stem tissues, dieback
"fine tunes" the tree's energy balance to its adverse environment.
With abatement of the defoliation stress, even if it has occurred for more than one season, trees can
recover providing growing conditions are favorable and providing they have not been lethally invaded by
opportunistic organisms that can attack them in their weakened state.
Organisms of Secondary Action: Armillaria mellea and Agrilus bilineatus and the coup de grace
Defoliation causes starch to be converted primarily to simple sugars such as glucose and fructose that
occur in relatively low quantities in nonstressed trees. This is important because Armillaria mellea, the
shoestring root attacking fungus (Fig. 12) , uses these sugars as energy sources for its growth. Thus, the
shift in energy within the tree initiated by defoliation favors the fungus and stimulates its rapid growth
between the bark and wood of roots and root collar. This girdling action by the fungus sounds the death
knell for many stressed trees.
Figure 12. The fungus Armillaria mellea is an organism of secondary action important in many dieback
decline diseases. It can be recognized by the characteristic shoestring-like rhizomorphs in the soil or
attached to roots, the white sheet-like fans of fungus mycelium between the bark and wood, and the
clusters of honey- colored mushrooms that appear near the base of trees in the fall.
Within individual trees, therefore, the defoliation process not only interrupts the conversion (flow) of
sunlight energy to chemical food energy, but also triggers the shift of chemical food energy from one
form to another (starch to sugars)-and ultimately from one organism to another (tree to fungus).
Although these energy relationships are probably most significant, defoliation does trigger other
biochemical changes (as yet not thoroughly understood) that may serve to reduce a tree's resistance to
attack, or increase an organism's pathogenicity. There is increasing evidence that the likelihood of a
defoliated tree being attacked and killed is influenced strongly both by tree condition and by complex
interactions between species of tree, strains of the fungus, and conditions of the site.
The twolined chestnut borer Agrilus bilineatus also has long been associated with dying oak trees (Fig.
13). Indeed, the obvious and characteristic galleries created by the borer as it tunnels between bark and
wood of main stems have led many to conclude that it is a much more important mortality-causing
agent than Armillaria, whose activity is mostly hidden below ground. Research has shown that either
organism in its respective arena can deliver the coup de grace and that extreme mortality can result
when they operate together.
Figure 13. The twolined chestnut borer Agrilus bilineatus (1) also is an important organism of secondary
action, responsible for the death of many oak trees weakened by stress. Often, trees girdled by the
meandering galleries of the borer (2) die quickly and retain their brown foliage for some time (3). Borer
damage can often be detected by the presence of D- shaped exit holes (4).
It is not known if A. bilineatus is affected by the same changes in trees that trigger attack by A. mellea.
Borers are attracted to trees under stress, probably by the release from such trees of a volatile chemical
produced in response to the stress. Trees that have been girdled, injured by lightning or wind,
droughted, or defoliated are attacked selectively.
The ability of a tree to withstand attack by the borer seems related to its physiological condition since
trees growing slowly before they are attacked are more likely to succumb than trees with good growth.
Thus, the tree's response to gypsy moth defoliation not only serves to attract this organism of secondary
action and to stimulate its attack, but also seems to reduce the tree's resistance to that attack.
Some Ecological Relationships
Effects of Oak Decline on Energy Flow and Material Cycling in the Forest
Energy flows but one way through a forest ecosystem. It enters the system as light, is transferred within
the system as chemical food, and exits the system as heat. It does not recycle. Essential nutrients, on the
other hand, cycle continually within the ecosystem.
The defoliation process results directly in the shunting of the normal flow of energy from leaves to tree
cells to soil microorganisms (the "detrital circuit"), to a flow from tree leaves to gypsy moth (the "grazing
circuit") (Fig. 14). The shunted energy continues its one-way flow through a number of gypsy mothinitiated food chains.
Figure 14. In the nondefoliated forest (left), sunlight energy is converted by tree leaves to chemical food
energy. This energy is used in tree growth and maintenance (1) and is stored in roots as starch (2), and
finally flows through a "detritus circuit" as microorganisms decompose fallen leaves and other dead
plant parts (3). When gypsy moth defoliates the forest (right), the energy flow is shunted into a "grazing
circuit" and passes through a number of food chains that begin with the gypsy moth (4). Some potential
chemical food energy and nutrients may pass out of the ecosystem in leaf fragments and insect frass (5)
but this probably is of little importance.
Since all materials essential for growth cycle within the ecosystem, defoliation, though it temporarily
interferes with normal pathways, probably affects relationships of nutrients less seriously than those of
energy. Significant amounts of nutrient-rich insect frass and leaf fragments could be washed from
watersheds (Fig. 14), but such an event is probably rare and of little long-range consequence.
Some Forest Influences
Energy flow and nutrient cycling are the driving forces behind the relatively orderly biological
development of a forest. Ecologists call this development "succession." Stresses such as those that
initiate oak decline, together with the tree mortality that follows, can materially alter the course of
forest succession.
In the moderately moist northern states of New England, the development of hardwood forest,
following agriculture or disturbance by heavy logging or fire, often begins with stands rich in such shortlived pioneers as gray or white birch and aspen. Later, these species are replaced, first with early-stage,
longer lived oaks and eventually by more shade tolerant species such as red oak, sugar maple, beech,
and hemlock. Most oaks in these forests are relatively transient, and their dominance of the site is
usually for short periods.
Moderately heavy defoliation of these forests by the gypsy moth often serves to accomplish in a short
time what succession would do eventually, especially if forest development is well advanced. The reason
for this is that gypsy moths prefer the early-stage species. In mixed forests, preferential defoliation
tends to reduce the relative proportion of these early-stage species, leaving forests richer in species
characteristic of more successionally mature forests. Severe, repeated defoliation, however, can result
in considerable tree mortality, even among species that are generally less favored by the gypsy moth.
In some southern New England states, oaks tend to be more numerous and to dominate the forest for
longer periods. In such situations, most of the trees were eliminated from the stand.
Susceptible vs. Resistant Forests Site conditions strongly influence where gypsy moth defoliation will
occur. In New England, where gypsy moths and forests have interacted for over a century, some forests
have had a history of repeated defoliation while others have been defoliated only rarely (Fig. 15). The
often defoliated or susceptible forests characteristically grow on dry sites such as rocky ridges or deep
sands. In many cases, they have been disturbed (sometimes frequently) by fire, wind, snow, or ice
storms. The trees in these forests, mainly dry-site oaks, often are highly favored as food by gypsy moths,
are slow growing, small, and scrubby, and have abundant structural features such as bark flaps, deep
bark fissures, and holes or wounds that are used as resting sites by gypsy moths.
Figure 15. Susceptible forests of New England characteristically grow on disturbed sites such as rocky
ridges (1) or deep sands (2). The trees in these forests often are highly preferred as food by gypsy moths,
slow growing, small, and scrubby, and have many structural features that serve as refuges for the insect.
The resistant forests of this region (3) characteristically grow on relatively undisturbed sites with welldrained, deep loam soils where moisture is not limiting. Resistant stands contain mixtures of species
including highly preferred ones, but they have relatively few structural features used by gypsy moths.
The open nature of susceptible forests encourages the growth of plants such as blueberry, huckleberry,
bracken, sweet fern, grasses, and sedges. Leaf litter usually is shallow or lacking; on ridge stands, surface
rocks or exposed ledges are common.
Resistant forests where defoliation is rare characteristically grow on relatively undisturbed sites with
well-drained, deep loam soils where moisture is not limiting. They usually are well stocked and contain
mixture of species, including some that are highly preferred. Trees on these sites have good growth
rates and relatively few structural features used by gypsy moths.
Understory plants in New England's resistant forests include such species as wild sarsaparilla, mapleleafed viburnum, and woodland ferns. Resistant stands have deep litter layers that are favorable habitat
for many predators of gypsy moth.
It is not axiomatic that trees growing on susceptible sites are more apt to succumb to a given defoliation
regimen than trees on resistant sites. Studies suggest that trees on adverse sites may be no more
(indeed, may even be less vulnerable) than trees on good sites. Perhaps this reflects the fact that trees
on poor sites represent the survivors of an exceptionally intense and continual selection process.
Physiological Performance and Condition: Reflections of the Past
Oaks growing on a good site may look quite different from those of the same species growing on a poor
one (Fig. 16). These differences reflect the responses of trees to site-related limitations in soil moisture
and nutrients, or to site-related disturbances.
Figure16. The appearance of trees reflects their response to site quality or disturbance. Compared with
the undisturbed chestnut oak on the good site (right), the tree of the same age on the poor site (left) has
a smaller, shorter crown, a thinner stem with narrow growth rings, a narrow band of sapwood, deeper
bark fissures, and a smaller root system. Wounds often remain open longer on slow-growing trees.
Severe disturbances such as drought, frost, or insect defoliation can occur on any site. Tree responses to
these external disturbances include dieback of buds, twigs, and branches, and small, sparse, off-color
foliage, and low or depleted root starch content in the fall.
Site-Related Characteristics
Chestnut oaks on adverse sites (left) grow more slowly than on good ones (right). This is reflected
externally by smaller, shorter crowns, smaller stem diameters, and deeper bark fissures, and internally
by narrow annual growth rings of stems and roots and a relatively narrow band of light-colored
sapwood. Because slow-growing trees do not close wounds rapidly, trees on adverse sites often bear
open wounds from branch stubs or injuries caused by storms or fire. Even on good sites some trees
appear poorer than others. Often, this is a reflection of the inherently different capabilities of individual
trees to grow and to compete for light, moisture, and nutrients. On good sites, these trees will drop by
the wayside as the stand develops. These internal and external characteristics constitute a tree's record
of physiological performance; that is, how well it has performed in response to intrinsic site factors.
Disturbance- Related Characteristics
Extrinsic disturbances such as storms, fire, drought, frost, or defoliation occur on good sites as well as
bad, but these disturbances are more frequent and severe on exposed sites. The poor appearance of
oaks on adverse sites, therefore, reflects the response of these trees to a greater frequency and
intensity of both internal and external factors on those sites. The small inserts in Figure16 (crown and
roots) depict external and internal responses of trees, regardless of site, to disturbances such as severe
late spring frost, drought, and especially insect defoliation (see also Figure 11). Dieback of twigs and
branches, small, sparse, off-color leaves, and low or depleted root starch content in the fall are
indications that trees have been subjected to one or more of these severe stress factors. Because active
dieback symptoms- and especially root starch content-reflect tree responses to recent events, they are
better measures of current physiological condition than general records of physiological performance.
Taken together, these measurements can be used as an index of tree condition.
Indexing Tree Condition
Several methods of assessing tree condition are shown in Figure 17. A general assessment is made of a
tree's condition based on the relative position of the crown in the canopy, evidence of poor growth,
injuries, dieback, etc. Not illustrated, but of value, is an increment core to determine patterns of annual
growth rate. Root starch content is determined by removing a sample of wood from a large root with a
hammer and chisel, sectioning this with a microtome, and staining the thin sections with a solution of
potassium iodide. In this solution the starch turns purple, and sections rich in starch will be dark
compared with those with little or no starch.
Figure 17. Evaluating tree vigor or physiological condition can entail several steps. An assessment is
made of features that reflect general condition (1). Such features include relative size and position of
tree crowns in the forest canopy, the size and color of leaves, the relative amounts of live and dead
branches, and the relative rates of wound closure. Root starch content is determined from a sample cut
from a large root (2). Thin sections are stained with potassium iodide (insert, right). Starch can be
classed as high (dark sections), medium, and low to depleted (light sections). Low starch reveals trees in
poor condition (high risk), high starch reveals trees in good condition (low risk). Measurements of
electrical resistance (3) may someday be useful in determining tree vigor. Studies have shown that
cambial zone tissues in high- vigor trees have a lower resistance to pulsed electric current than those in
low-vigor trees.
The use of an electronic method for measuring tree condition is shown in Figure 17. Although still
experimental, readings of the electrical resistance of tissues near the cambial zone show promise of
providing another measure of tree condition. Readings of low electrical resistance are associated with
trees in good condition.
Root starch content not only reveals that trees have been stressed, but also may be of value in
predicting the consequences of additional stress. As shown in Figure 11, white oaks with little or no root
starch are more apt to die after defoliation than trees high in root starch. Knowing which trees or stands
are the greatest "risk" can help in planning actions to reduce losses of valuable trees.
Preventing and Reducing Oak Decline
Preventing gypsy moth-initiated oak decline entails, as with other dieback and decline diseases, actions
designed to maintain trees in good physiological condition, and to reduce the stress agent. In the
following sections, actions that can be performed in forest, campground, and urban environments to
prevent oak decline are discussed.
In Forests and Campgrounds
Actions in the forest are general ones, designed primarily to enhance the conditions of trees growing
there (Fig. 18). Silvicultural thinnings to remove trees in poor condition will reduce the numbers of trees
most vulnerable to the effects of stress, and will enhance growing conditions for the residual trees. And,
although not demonstrated, it is possible that removing weak and dying trees and the populations of
twolined chestnut borers associated with them will reduce mortality attributable to those organisms.
Weak and dying trees should be removed from campgrounds for the same reasons and also because
they can be hazardous. Removing weak and defective trees will eliminate many refuges for the gypsy
moth.
Monitoring gypsy moth populations will aid in determining when direct preventative actions must be
taken. Within a forest, stands known to be outbreak foci, or stands identified as potentially susceptible
(such as the oak-covered rocky ridge top in figure 18) would be good candidates for monitoring sites.
Figure 18. Preventing gypsy moth-initiated oak decline in the forest and campground includes such
diverse actions as monitoring populations in known outbreak foci (1) and in campgrounds (2) with
pheromone traps or burlap "skirts"; removing vulnerable, weak, or dying trees and thinning to improve
growing conditions for residual trees (3); eliminating from campgrounds trees that provide refuges for
gypsy moths (4); spraying with approved insecticides where severe defoliation is eminent and where
measurements of tree vigor indicate defoliation will result in high tree losses (5); and inspecting camping
vehicles and equipment in infested campgrounds to reduce the numbers of insects being transported
into uninfested regions (6).
Traps baited with the female sex pheromone attract adult male moths and are especially useful in
assessing insect populations in remote areas. In more accessible places such as campgrounds, burlap
"skirts" tied around favored host trees also can be used. These skirts provide a favorable resting site for
gypsy moth larvae, and they can be easily checked for numbers of larvae.
It is especially important to monitor gypsy moth populations in campgrounds within the generally
infested region to reduce the numbers of instances where insects on automobiles and camping vehicles
and equipment are transported into uninfested areas.
Spraying with approved insecticides may be required when severe defoliation is inevitable, and
especially if indexes of tree condition, such as low starch content, indicate that defoliation will trigger
significant losses of valuable trees. It may be more important to protect foliage in the campground than
in the forest.
In Urban Areas
Preventing gypsy moth-related oak decline in the urban backyard (Fig. 19) can include several practices
not feasible in the forest. Keeping valuable specimen trees healthy by watering, fertilizing, and mulching
is as important for preventing oak decline as it is for other dieback-decline diseases. In addition, several
activities will help keep insect populations low, especially where backyards and forest join. Removing
rubbish from yards, especially near the forest edge, will eliminate many favorite gypsy moth refuges.
Signs, old tires, tree houses, and wood piles are particularly favored places and should be inspected
carefully, and large, dead branches and other tree features that provide habitat for gypsy moths should
be removed.
Figure 19. Preventing gypsy moth-initiated oak decline in the backyard requires that trees be kept
healthy by fertilizing and mulching specimen trees (1); removing rubbish and natural refuges from
backyards and forest edges (2); inspecting and, when necessary, destroying insects occupying objects
such as tree houses, signs, picnic tables, and burlap skirts tied around trees to attract larvae (3);
destroying egg masses (4); spraying when necessary (5); and keeping layers of forest litter as
undisturbed as possible to encourage natural ground-inhabiting predators and to conserve soil moisture
(6).
Burlap skirts tied around preferred food trees are effective for both monitoring insect populations and
collecting insects for destruction. Egg masses can be removed and destroyed or treated in place with
creosote; when populations are high, trees can be sprayed with approved insecticides. Whenever
possible, layers of forest litter, home of many ground-inhabiting predators of gypsy moth, should be
maintained. Keeping humus layers intact also will help prevent the drying out of soil layers.
Selected References
General
Houston, D. R. 1967. The dieback and decline of northeastern hardwoods. Trees 28:12-14.
Houston, D. R. 1973. Diebacks and declines: Diseases initiated by stress, including defoliation. Int. Shade
Tree Conf. Proc. 49:73-76.
Houston, D. R. 1974. Diagnosing and preventing diebacks and declines. Morton Arbor. Q. 10(4):55-59.
Houston, D. R., J. Parker, and P. M. Wargo. 1981. Effects of defoliation on trees and stands: Chapter 5. In
The gypsy moth: Research toward integrated pest control. U.S. Dep. Agric. Tech. Bull. 1584.
Sinclair, W. A. 1964. Comparisons of recent declines of white ash, oaks, and sugar maple in northeastern
woodlands. Cornell Plant. 20:62-67.
Wargo, P. M. 1975. Estimating starch content in roots of deciduous trees-a visual technique. USDA For.
Serv. Res. Pap. NE313. 9 p.
Wargo, P. M. 1978. Judging vigor of deciduous hardwoods. U.S. Dep. Agric. Inf. Bull. 418. 15 p.
Wargo, P. M., and H. R. Skutt. 1975. Resistance to pulsed electric current: An indicator of stress in forest
trees. Can. J. For. Res. 5:557-561.
Ash Dieback
Brandt, R. W. 1961. Ash dieback in the northeast. USDA For. Serv. Northeast. For. Exp. Stn., Stn. Pap.
163. 8 p.
Ross, E. W. 1963. A pathogenic Fusicoccum sp. associated with ash dieback cankers. Plant Dis. Rep.
47:20-21.
Ross, E. W. 1966. Ash dieback-etiological and developmental studies. SUNY Coll. For. Tech. Publ. 88. 80
p.
Silverborg, S. B., and R. W. Brandt. 1957. Association of Cytophoma pruinosa with dying ash. For. Sci.
3:75-78
Beech Bark Disease
Ehrlich, J. 1934. The beech bark disease, a Nectria disease of Fagus following Cryptococcus fagi (Baer.),
Can. J. Res. 10:593-692.
Houston, D. R. 1975. Beech bark disease: The aftermath forests are structured for a new outbreak. J.
For. 73:660-663.
Houston, D. R., E. J. Parker, R. Perrin, and K. J. Lang. 1979. Beech bark disease: A comparison of the
disease in North America, Great Britain, France and Germany. Eur. J. For. Path. 9:199-211.
Shigo, A. L. 1962. Another scale insect on beech. USDA For. Serv. Northeast. For. Exp. Stn. Stn. Pap. 168,
13 p.
Shigo, A. L. 1964. Organism interactions in the beech bark disease. Phytopathology 54:263-269.
Maple Decline Giese, R. L., D. R. Houston, D. M. Benjamin, J. E. Kuntz, J.E. Kapler, and D. D. Skilling. 1964.
Studies of maple blight. Univ. Wis. Res. Bull. 250. 128 p.
Parker J. 1970. Effects of defoliation and drought on root food reserves in sugar maple seedlings. USDA
For. Serv. Res. Pap. NE-1 69. 8 p.
Parker, J., and D. R. Houston. 1971. Effects of repeated defoliation on root and root collar extractives of
sugar maple trees. For. Sci. 17:91-95.
Wargo, P. M. 1972. Defoliation-induced chemical changes in sugar maple roots stimulate growth of
Armillaria mellea. Phytopathology 62:1278-1283.
Wargo, P. M. 1977. Wound closure in sugar maples: Adverse effects of defoliation. Can. J. For. Res.
7:410-414.
Wargo, P.M., and D. R. Houston. 1974. Infection of defoliated sugar maple trees by Armillaria mellea.
Phytopathology 64:817-822.
Wargo, P. M., J. Parker, and D. R. Houston 1972. Starch contents in roots of defoliated sugar maple. For.
Sci.. 18:203-204.
Oak Decline
Dunbar, D. M., and G. R. Stephens. 1975. Association of twolined chestnut borer and shoestring fungus
with mortality of defoliated oak in Connecticut. For. Sci. 21:169-174.
Houston, D. R. 1971. Noninfectious diseases of oak. In Oak symposium proceedings. USDA For. Serv.
Northeast. For. Exp. Stn., Upper Darby, Pa. p. 118-123.
Houston, D. R. 1979. Classifying forest susceptibility to gypsy moth defoliation. U.S. Dep. Agric., Agric.
Handb. 542, 24 p.
Houston, D. R., and H. T. Valentine. 1977. Comparing and predicting forest stand susceptibility to gypsy
moth. Can. J. For. Res. 7:447-461.
Kegg, J. D. 1973. Oak mortality caused by repeated gypsy moth defoliation of oak in New Jersey. J. Econ.
Entomol. 66:639-641.
McManus, M. L., D. R. Houston, and W. E. Wallner. 1979. The homeowner and the gypsy moth:
Guidelines for control. U.S. Dep. Agric. Home and Gard. Bull. 227. 34 p.
Nichols, J. 0. 1968. Oak mortality in Pennsylvania. A 1 10 year study. J. For. 66:681-694.
Parker, J., and R. L. Patton. 1975. Effects of drought and defoliation on some metabolites in roots of
black oak seedlings. Can. J. For. Res. 5:457-463.
Skelley, J. M. 1969. Oak decline. Va. Polytech. Inst. and State Univ. Ext. Serv. Bull. MR-FTD-4.
Staley, J. M. 1965. Decline and mortality of red and scarlet oaks. For. Sci. 11:2-17.
Valentine, H. T., and D. R. Houston. 1979. A discriminant function for identifying mixed-oak stand
susceptibility to gypsy moth defoliation. For. Sci. 25:468-474.
Wargo, P. M. 1976. Variation of starch content among and within roots of red and white oak trees. For.
Sci. 22:468-471.
Wargo, P. M. 1977. Armillariella mellea and Agrilus bilineatus and mortality of defoliated oak trees. For.
Sci. 23:485-492.
Wargo, P. M. 1978. Defoliation by the gypsy moth: How it hurts your tree. U.S. Der). Agric. Home and
Gard. Bull. 223. 15 p.
Wargo, P. M. 1978. Insects have defoliated my tree-now what's going to happen? J. Arboric. 4:169-175.
Discolouration and decay associated with paraformaldehyde-treated tapholes in sugar maple
Research
USDA Forest Service
Russell S. Walters And Alex L. Shigo, US. Department of Agriculture, Forest Service, Northeastern Forest
Experiment Station, 6816 Market Street, Upper Darby; PA, U.S.A. 19082
Can. J. For. Res. 8: 54-60.
1978
REF# 292
Abstract
More decay (higher incidence and greater total length of column) was associated with tapholes in
mature sugar maples (Acer saccharum Marsh.) treated with a 250-mg paraformaldehyde pill than with
control tapholes. This was apparent 20 months after treatment and at each successive examination to
the final measurement at 56 months. Discoloured columns associated with pill-treated tapholes were
longer than those associated with control tapholes for the first 8 months. From that time until the final
measurement there were no statistically significant differences between lengths of discoloured columns
associated with pill-treated and control tapholes. Cambial dieback occurred adjacent to many tapholes
but there was no significant difference in closure rates of treated and control tapholes. Results were
obtained from dissections and studies of 180 mature trees over a 56-month period in six locations in
Vermont in one experiment, and from 75 trees over a 20-month period in three locations each in
Vermont, Maine, New York, Pennsylvania, and Michigan in another experiment. The results indicate that
repeated use of paraformaldehyde will lead to rapid development of decay in sugar maple trees.
Les auteurs ont observé plus de caries, (incidence plus forte et longueur plus grande de la colonne de
coloration) chez les entailles d'arbres mûrs d'érable à sucre (Acer saccharum Marsh.) traitées au moyen
d'une pastille de 250 mg de paraformaldehyde, comparativement aux entailles non traitées. Cette
observation était apparente 20 mois après traitement et à chaque examen successif jusqu'aux mesures
finales à 56 mois. Les colonnes de coloration associées aux entailles traitées à la paraformaldehyde
étaient plus longues apres les huit premiers mois. A partir de ce temps jusqu'aux mesures finales, on n'a
pas observé de differences significatives entre les traitements dans la longueur des colonnes de
coloration. Le dépérissement cambial s'est manifesté près de plusieurs entailles mais on n'a pas observé
de différences dans le taux de cicatrisation des entailles en fonction des traitements. Les résultats sont
le fruit de deux expériences: l'une portant sur 180 arbres mars pour une période de 56 mois dans six
localites du Vermont, l'autre portant sur 75 arbres soumis à une observation de 20 mois dans trois
localités de chacun des états du Vermont, du Maine, de New York, de Pennsylvanie et du Michigan. Les
résultats indiquent que 1'emploi répété de la paraformaldehyde est susceptible de conduire au
développement rapide de caries chez l'érable à sucre. [Traduit par le journal]
Introduction
Paraformaldehyde (trioxymethylene) pills are sometimes used in tapholes in sugar maple (Acer
saccharum Marsh.) to increase and prolong the yield of sap collected for making syrup and sugar
(Costilow et al. 1962; Sheneman et al. 1959). The explanation for the increase in sap yield is that the
paraformaldehyde inhibits the growth of microorganisms in the taphole (Costilow et al. 1962; Sheneman
and Costilow 1959) that can cause restriction and stoppage of the sap flow (Ching and Mericle 1960;
Naghski and Willits 1955). Results of a short-term study by Shigo and Laing (1970) suggested that
paraformaldehyde was associated with internal injury of wood that could lead to more rapid
development of decay.
This paper is a report on results of long-term studies started in 1970 to compare paraformaldehydetreated and control tapholes. Such information is needed to help clarify the early stages of the wound
response in trees and the factors that affect development of decay.
Materials and Methods
Vermont Study
In February 1970. 240 sugar maples 20-35 cm in diameter at 1.4 m aboveground in the vicinities of
Brandon, Quechee, Willoughby, Ripton, Tinmouth, and Groton, Vermont, were selected for tapping.
Forty trees in each location were tapped 24-26 February 1970, by drilling 2 holes 1.1 cm in diameter and
7.6 cm deep at least 15 cm apart horizontally at a height of 1.5 m above the ground on the side of the
trunk facing south. By random selection, a 250-mg paraformaldehyde pill was put in one taphole in each
tree immediately after drilling; the other taphole was the control. Plastic spouts, inserted in each
taphole, were removed 2 months later. No sap was collected. All tapping was done according to
industry-accepted standards (Willits 1965).
Randomly selected trees in each location were harvested, five each at 2, 8, 20, 32, 44, and 56 months. A
1.5 m bolt of wood from each tree, with the tapholes in the middle, was taken to a laboratory for
dissection and study. One bolt from each location collected from the 2- and 8-month harvests, and two
bolts from each location from the other harvests were used for isolation of microorganisms.
These bolts were first cut and split into two billets, each approximately 50 x 8 x 8 cm, with the taphole in
the center. The billets were then split through the taphole with a sterile ax. A sterile gouge was used to
cut out 12 or 24 chips, 3 x 3 x 10 mm, from the discoloured or discoloured and decayed wood associated
with the taphole. The chips were placed in petri dishes in a medium consisting of 10 g malt extract, 2 g
yeast extract, and 20 g agar per litre of distilled water. The cultures, incubated at 25°C in darkness, were
examined several times over a period of 30 days.
In these studies, discoloured wood was considered as wood altered in colour only (no strength loss). The
cell contents were altered as a result of interactions between the tree and microorganisms. Decayed
wood was wood that had cell walls digested (a loss in strength). Decayed wood was found to be softer
or weaker than surrounding tissues when probed by a sharp instrument.
The lengths of the columns of discoloured and decayed wood were measured. If the columns extended
beyond the limits of the billets, the bolts that yielded the billets were split further. This procedure was
also followed when columns extended beyond the limits of the 1.5-m bolts. In addition, all bolts not
used for isolations were also split longitudinally through the tapholes, and the length of the columns of
discoloured and decayed wood above and below each taphole was measured.
Northeast Region Study
In March 1973, 300 sugar maples 25-58 cm in diameter at 1.4 m aboveground were tapped, using the
same procedures given above; there were 20 trees in each of three locations in the following five states:
Pennsylvania (Windy City, Pig's Ear, and Lamont); Maine (Auburn, Buckfield, and Hebron); Michigan
(Decatur, East Lansing, and Sault Ste. Marie); New York (Brandon, Van Etten and Warrensburg); and
Vermont (Victory, Cobb Hill, and Groton).
Five randomly selected trees from each of the 15 locations were harvested 20 months after tapping, and
the lengths of discoloured and decayed wood associated with each taphole were measured, using the
same procedures given for the Vermont study. Two trees from each location were also used for isolating
microorganisms.
The column-length data for both discolouration and decay were subjected to analysis of variance, and
the data on incidence of decay were subjected to chi-square tests. The taphole-closure data were
analyzed, using the t-test for paired replicates.
Results
Discoloured Wood
Discoloured wood was associated with all tapholes. In the Vermont study, there was a highly significant
difference between the lengths of discoloured columns associated with pill-treated and control tapholes
after 2 months. The columns associated with the 2-month-old control tapholes were uniformly small,
approximately 2 cm, while columns associated with the pill-treated tapholes were uniformly large,
approximately 13 cm (Fig. 1, Table 1). The same trend was still present after 8 months, but there was
much less difference between the column lengths of the pill-treated and control tapholes. By 20
months, the columns were approximately the same length.
Figure 1. Discoloured wood associated. with 2-month-old tapholes. Left, pill-treated; right, control. The
small pits mark where chips were taken for microorganisms.
Table 1. Average lengths of columns of discoloured wood associated with paraformaldehyde-treated
and control tapholes in sugar maples treated February 1970 in Vermont (in centimetres)
Treated (+)
Time after treatment, months
or
Location
control (-)
2
8
20
32
44
Brandon
+
15
51
80
65
99
84
-
2
42
63
76
98
83
14
62
75
81
119
99
2
48
64
58
76
80
+
14
58
74
77
141
2
46
73
76
148
87
13
51
69
61
94
51
-
3
45
55
59
81
49
Quechee
+
14
48
84
80
97
-
2
36
68
72
83
95
Groton +
Willoughby
Ripton +
90
86
56
Tinmouth
+
10
56
84
117
122
-
4
65
73
83
85
92
X, Totals
+
13
54
78
80
112
-
2
47
66
71
95
81
100
85
Note: Each figure is the mean of five tapholes. Length of total column above and below taphole.
Decayed Wood
There was no decay in any of the samples from the 2- and 8-month harvests. Most of the pill-treated
tapholes in the later harvests had significantly more decay (higher incidence and greater length of
columns) than the control tapholes (Table 2, Fig. 2).
Figure 2. Dissection of two 20-month-old tapholes, showing greater discolouration and decay in the pilltreated taphole (left) than in the control taphole (right).
Table 2. Lengths (in centimetres) of decay columns (and number of trees with decay) associated with
paraformaldehyde. treated and control tapholes in sugar maples treated during February 1970 in
Vermont. Data from five trees at six locations for each period: 20, 32, 44, and 56 months
Treated (+)
Time after treatment, months
or
Location
control (-)
Brandon
+
39 (5) 32 (5) 50 (5) 34 (5)
8 (3)
22 (4) 16 (2) 11 (4)
Groton +
Willoughby
Ripton +
Quechee
-
20
32
44
33 (5) 34 (5) 55 (5) 64 (5)
7 (3)
15 (3) 10 (1) 26 (4)
+
27 (4) 35 (5) 69 (5) 37 (3)
9 (2)
22 (4) 22 (4) 17 (3)
30 (4) 27 (5) 22 (4) 5 (2)
4 (1)
20 (4) 20 (4) 8 (2)
+
33 (4) 27 (5) 10 (1) 52 (5)
6 (2)
21 (4) 21 (1) 22 (3)
56
Tinmouth
X, Totals
-
+
28 (5) 29 (5) 43 (4) 37 (5)
2 (2)
9 (3)
+
32 (37) 31 (30) 42 (24) 38 (25)
7 (2)
22 (4)
6 (13) 18 (22) 16 (14) 20 (20)
Regional Study
The results of the 20-month harvest of the regional study were similar to those of the Vermont study for
harvests of 20 months and thereafter (Table 3). There was no significant difference between the lengths
of discoloured columns associated with pill-treated and control tapholes. But the incidence of decay and
the lengths of decay columns associated with pill-treated tapholes were significantly greater than for
controls. The results were the same for all locations. There were no differences among states nor among
locations within states.
Table 3. Average lengths (in centimetres) of discoloured and decayed columns above and below 20month- old paraformaldehyde- treated and control tapholes on five trees from three locations each in
five states
Locations
Treated (+)
1
2
3
1
2
3
or
State
control (-)
Pennsylvania
Discoloured wood
Decayed wood
+
50
73
55
1.(2)
T.(1)
48
67
63
0
0
T.(1)
+
60
47
48
9.(2)
10.(2) 1.(1)
-
58
54
49
0
0
0
Maine +
70
46
51
40.(5) 0
9.(1)
-
52
43
53
3.(1)
0
2.(l)
+
62
63
50
7
7.(2)
57
57
46
0
0
T.(1)
+
44
54
61
9.(2)
0
44
53
59
T.(1)
0
2.(2)
Vermont
Michigan
New York
-
0
3.(1)
10.(3)
Microorganisms
More chips from wood tissues associated with pill-treated tapholes yielded wood-destroying fungi
(Hymenomycetes) in culture than did chips from tissues associated with the control tapholes (Table 4).
The principal Hymenomycete isolated was Coriolus (Polyporus) versicolor (L. ex. Fr.) Quel. (Fig. 3).
Figure 3. Dissection of two 32-month-old tapholes. Left pill-treated; right, control. Note the large areas
of cambial dieback associated with the tapholes. Decay in the pill-treated specimen was caused by
Coriolus versicolor.
Bacteria were the principal microorganisms isolated from the 2-month-old columns of discoloured wood
(Table 4). Hymenomycetes were isolated from all six trees after 8 months, but from only one control
taphole. Where Hymenomycetes were isolated, no Phialophora spp. and few other
nonhymenomycetous fungi were isolated (Table 4). A similar pattern was seen in the older samples, but
in some cases, a few chips from columns yielding Hymenomycetes did yield Phialophora spp. From the
20-month-old tapholes from the regional study, bacteria were the principal microorganisms isolated
(Table 5). Again, when Hymenomycetes were isolated, a few other chips yielded Phialophora spp. The
pattern appeared to be that where many chips yielded bacteria, nonhymenomycetous fungi, and
Phialophora spp., specifically, few or no chips yielded Hymenomycetes (Tables 4, 5).
Table 4. Percentage of isolation chips that yielded microorganisms from discoloured and decayed wood
associated with paraformaldehyde-treated and control tapholes in Vermont. Treatment was in February
1970
Time after
Micro-
treatment,
organisms
months No. Trees
found Treated Control
2
8
6
6
B
89
100
P
6
6
N
8
13
H
0
0
B
18
60
P
0
29
N
31
54
H
71
4
B
23
49
20
32
44
56
12
12
11
12
P
2
12
N
20
53
H
61
9
B
69
91
P
15
44
N
51
54
H
33
8
B
50
70
P
19
23
N
34
37
H
28
9
B
91
76
P
21
25
N
48
51
H
3
8
NOTE: Individual tree data are available from the authors.
B = bacteria
P = Phialophora spp.
N = all other nonhymenomycetous fungi
H = Hymenomycetes.
Table 5. Percentage of isolation chips that yielded microorganisms from discoloured and decayed wood
associated with paraformaldehyde-treated and control tapholes after 20 months, in Pennsylvania, New
York, Michigan, and Maine
Treated
Microorganisms
or
State
control B
P
N
H
Pennsylvania
+
100
3
46
89
42
24
0
+
90
18
44
99
29
50
0
+
90
19
46
100
28
32
12
Maine +
49
7
46
35
-
83
24
48
6
New York
Michigan
-
0
15
15
NOTE: Individual tree data are available from the authors.
Taphole Closure
Large areas of dead cambium were associated with some tapholes (Fig. 3). Measurements of lengths
and widths of the dead areas were made on the trees -harvested after 8 months. The average lengths
were 66 and 60 mm for the treated and control tapholes, respectively. The respective average widths
were 22 and 23 mm. These differences were not significant. Cambial dieback was not associated with
use of the paraformaldehyde pill.
Measurements of taphole closure and lengths of areas of dead cambium were also made on the trees
harvested after 32 months. Fully closed tapholes were first observed at this harvest. Thirty percent of
the treated tapholes and 23% of the control tapholes were completely closed. There were no
statistically significant differences between pill-treated tapholes and controls in either numbers of
tapholes closed or areas of dead cambium.
In the final harvest, 56 months after tapping, 82 % of the treated tapholes and 93 % of the control
tapholes were completely closed. All open control tapholes occurred on trees that also had open treated
tapholes.
Discussion
The results indicated that paraformaldehyde had a profound effect on the establishment and
development of decay associated with tapholes in sugar maple. This reinforces the data presented by
Shigo and Laing (1970). Houston (1971) showed that when decay developed in paraformaldehydetreated increment-borer holes in red maple (Acer rubrum L.), the columns were longer than those
associated with 11 other treatments. Yet in his study no decay was associated with paraformaldehydetreated holes in yellow birch (Betula alleghaniensis Brit.). Paraformaldehyde may have a specific effect
on species of Acer.
The columns of discoloured wood associated with pill-treated tapholes were significantly longer than
those of the control wounds after 2 and 8 months. In the samples taken after this period, there was no
difference in column length between the treated and control tapholes. The incidence and extent of
decay in treated tapholes were significantly greater than in control tapholes. Shigo and Sharon (1970)
showed that columns of discoloured wood associated with taphole-like wounds in sugar maple were
approximately the same length in all their study trees after 8 years and were similar to those reported in
this study for 56 months. This suggests that columns of discoloured wood develop very rapidly in the
first few years after a wound is inflicted, and very slowly thereafter. Although it is this discoloured wood
that is subsequently invaded by decay fungi, a different system apparently operates for the
development of decay. Shigo and Sharon (1970) showed great variations in the lengths of decay columns
associated with 8-year-old taphole-type wounds.
This same variation was also shown in this study. Further, Sharon (1973, 1974) showed that chemical
and morphological changes occur rapidly in sugar maple after wounding. The data from other studies
(Sharon 1973, 1974), and from this study, suggest that the processes that occur soon after wounding
may determine, to a great extent, the events to follow. It may be that paraformaldehyde alters an
important part of the natural defense system initiated by wounding. Sharon (1973) conjectured that
paraformaldehyde may have a direct injurious effect on the contact cells, those cells that connect the
vascular and parenchymal systems. The contact cells are very active from late winter until spring in
sugar maple (Sauter et al. 1973), and have a direct effect on the plugging system in vessels. Plugs form
soon after wounds are inflicted (Rier and Shigo 1972; Sharon 1973). If the contact cells are injured and
plugging is delayed, the flow of sap through the wound will increase; but, if plugging is a vital part of the
tree's defense system, a stalling of this system would facilitate invasion by Hymenomycetes.
Another possible explanation of the mode of action of paraformaldehyde is that it may alter other
chemicals, such as the oxidized phenols, that are formed by the tree as defense barriers. These
chemicals occur in wound-altered living xylem cells and often inhibit many wound-infecting
microorganisms (Shortle et al. 1971; Tattar and Rich 1973). Yet some pioneer nonhymenomycetous
fungi, such as Phialophora spp., grow very well on those substrates and probably modify them, allowing
subsequent invasion by the Hymenomycetes (Tattar et al. 1971 ). If paraformaldehyde does alter the
phenolic compounds, or stall their formation, then the usual group of wound-infecting pioneers could
not compete for the substrates. And, if the xylem cells are killed before such chemical barriers can form,
then the Hymenomycetes could have easy access to the wood. Microorganisms associated with the
control tapholes followed the usual successional pattern of bacteria, Phialophora spp., and few
Hymenomycetes (Shigo 1976; Tattar et al. 1971). On the other hand, after 8 months the
paraformaldehyde- treated tapholes yielded many Hymenomycetes and no Phialophora spp. The normal
successional pattern appears to have been shortened or bypassed.
It is not understood why some tapholes develop large areas of cambial dieback and fail to close. Injuries
caused by paraformaldehyde were suspected as a cause, but we did not find a relationship between use
of the pill and amount of dead cambium, or lack of taphole closure. Generally, treated and control
tapholes on the same tree reacted the same and were either open or closed, and the resulting areas of
dead cambium were about the same size. Rate of taphole closure was related to conditions within the
tree. This agrees with Neely's (1970) determination that the most important factors affecting treewound closure (healing) were tree vigor and wound size.
The results of these studies showed that paraformaldehyde did have an effect on the decay process. The
effect is one that occurs early in the process, and it offers an explanation to help clarify the early
changes that affect the decay process.
Our results are in agreement with those of MacArthur and Blackwood (1966) in that they indicate that
repeated use of paraformaldehyde can cause rapid decay development in sugar maples. The short-range
benefits of greater sap yield must be weighed against the long-range damage to the trees and an
eventual great decrease in sap yield.
Acknowledgement
The authors are grateful to Dr. Frances F. Lombard, mycologist, Center for Forest Mycology Research,
Forest Products Laboratory, Madison, Wisconsin, for verifying the identification of Coriolus (Polyporus)
versicolor (L. ex Fr.) Quél.
Ching. T. M., And L. W. Mericle.
1960. Some evidence of premature stoppage of sugar maple sap production. For. Sci. 6: 270-275.
Costilow. R. N.. P. W. Robbins. And R. J. Simmons.
1962. The efficiency and practicability of different types of paraformaldehyde pellets for controlling
microbial growth in maple tree tapholes. Mich. Agric. Exp. Stn. Quart. Bull. 44: 559-579.
Houston. D. R.
1971. Discoloration and decay in red maple and yellow birch: reduction through wound treatment. For.
Sci. 17: 402-406.
Macarthur. J. D.. And A. C. Blackwood.
1966. Taphole sanitization pellets and sugar maple sap yield. For. Chron. 42(4): 380-386.
Naghski. J.. And C. O. Willits.
1955. Maple syrup. IX Microorganisms as a cause of premature stoppage of sap flow from maple tap
holes. Appl. Microbiol. 3: 149-15 1.
Neely. D.
1970. Healing of wounds on trees. J. Am. Soc. Hortic. Sci. 95: 536-540.
Rier. J. P., And A. L. Shigo.
1972. Some changes in red maple. Acer rubrum. tissues within 34 days after wounding in July. Can. J.
Bot. 50: 1783-1784.
Sauter. J. J.. W. Iten. And M. H. Zimmermann.
1973. Studies on the release of sugar into vessels of sugar maple (Acer saccharum). Can. J. Bot. 51: 1-8.
Sharon, E. M.
1973. Some histolog-cal features of Acer saccharum wood formed after wounding. Can. J. For. Res. 3:
83-89.
1974. An altered pattern of enzyme activity in tissues associated with wounds in Acer
saccharum. Physiol. Plant Pathol. 4: 307-312.
Sheneman. J. M., And R. N. Costilow.
1959. Identification of microorganisms from maple tree tapholes. Food Res. 24: 146-151.
Sheneman. J. M., R. N. Costilow, P. W. Robbins, And J. E. Douglass.
1959. Correlation between microbial populations and sap yields from maple trees. Food Res. 24: 152159.
Shigo, A. L.
1976. Microorganisms isolated from wounds inflicted on red maple, paper birch, American beech. and
red oak in winter, summer, and autumn. Phytopathology, 66:559-563.
Shigo, A. L.. And F. M. Laing.
1970. Some effects of paraformaldehyde on wood surrounding tapholes in sugar maple trees. U.S. Dep.
Agric. For. Serv. Northeast. For. Exp. Sin. Res. Pap. NE-161.
Shigo, A. L.. And E. M. Sharon.
1970. Mapping columns of discolored and decayed tissue in sugar maple, Acer saccharum.
Phytopathology, 60: 232-237.
Shortle. W. E.. T. A. Tattar. And A. E. Rich.
1971. Effects of some phenolic compounds on the growth of Phialophora melinii and Fomes connatus.
Phytopathology, 61: 552-555.
Tattar, T. A.. And A. E. Rich.
1973. Extractable phenols in clear, discolored, and decayed woody tissues and bark of sugar maple and
red maple. Phytopathology, 63: 167-169.
Tattar. T. A.. W. C. Shortle, And A. E. Rich.
1971. Sequence of microorganisms and changes in constituents associated with discoloration and decay
of sugar maples infected with Fomes connatus. Phytopathology, 61: 556-558.
Willits. C. O.
1965. Maple syrup producers' manual. U.S. Dept. Agric. Agric. Handb. 134.
Stem Decay in Living Trees in Ontario’s Forests: A User’s Compendium and Guide
Extension
Forestry Canada, Ontario Region, Great Lakes Forestry Centre
J.T. Basham
Information Report O-X-408
1991
REF# 385
Abstract
All of the commercially important tree species of Ontario are affected to some degree by internal stem
decay or stain. These defects can have a serious impact on harvesting costs and efficiency and on
product values. For the most part they are hidden defects, and therefore difficult to assess or predict.
Without burdening the reader with unnecessary scientific and technical details, this report outlines the
stem-decay process, the ways in which the extent of stem decay can be assessed, the economic impact
of stem decay, and the methods that can be used to combat stem decay. Individual sections on each of
the major forest-tree species of Ontario deal with stem-decay relationships, causes, external symptoms,
and the minimization of the impact of decay through silvicultural and management procedures.
Résumé
Toutes les essences d’importance industrielle de l’Ontario sont touchées, à un degré ou à un autre, par
la carie ou les taches colorées de la tige. Ces défauts internes, la plupart du temps cachés, donc difficiles
à évaluer ou à prédire, peuvent avoir des répercussions graves sur les coûts et l’efficacité de la récolte
ainsi que sur la valeur des produits. Sans ennuyer le lecteur de détails scientifiques et techniques
inutiles, le rapport décrit le processus de la carie, les façons d’en évaluer la gravité, les répercussions
économiques et les méthodes qui peuvent être utilisées pour la combattre. Des sections sont affectées à
chacune des principales essences forestières de l’Ontario et s’occupent des relations, des causes et des
symptômes extérieurs de la carie des tiges de même qu’elles cherchent à en réduire au minimum les
répercussions par des méthodes d’aménagement et de sylviculture.
Introduction
My aim in this report is to provide forest managers and others with information on combating or
avoiding heavy losses from stem decay. A considerable body of literature on stem decays in Ontario and
in adjacent provinces or states has been published over the past 50 to 60 years. Much of it, however, is
highly technical, and of limited use to the field foresters who are responsible for dealing directly with
decay problems. In this report I attempt to summarize, from those publications and from my own
unpublished data and observations, all information on stem decays in living trees that I am aware of that
might be helpful to users in the field, particularly in Ontario.
In 1947, when the Canadian government first became involved in forest pathology research in Ontario,
the provincial forestry department had very little information on stem decay. What it did have was
based almost entirely on timber-scaling experience and on observations made during harvesting
operations. Each major tree species was more or less arbitrarily assigned a single percentage figure to
represent the volume of stem decay, a cull-factor “guesstimate”. Federal researchers believed, on the
basis of investigations carried out in other provinces and countries, that this was a very misleading and
inaccurate policy. In 1947 and 1948, they initiated three studies on stem decays (which represented
about 50% of their total research program), partly because of requests received from the province and
the forest industry. It soon became clear that in Ontario, as elsewhere, the incidence of decay in
individual tree species could differ greatly among locations as a result of several factors, including tree
age, diameter, site conditions, geographic region, cover type, and stand history. In a cooperative study
conducted from 1952 to 1957, federal and provincial researchers felled, dissected and carefully
measured the extent of decay in 22,739 trees of commercial size throughout Ontario’s Boreal and Great
Lakes-St. Lawrence forest regions. Though designed primarily for forest-inventory purposes, this survey
provided the first accurate cull (decay) factors and relationships for most of the commercially important
forest tree species in Ontario. In the early 1970s, questionnaires sent to 182 hardwood-processing
industries in southern Ontario south of the Canadian Shield formed the basis of a report on decay
problems in hardwood tree species in the Deciduous Forest Region of Ontario (Basham 1973a).
I was involved in stem-decay investigations in Ontario for roughly 30 years. In addition, I studied the
deterioration of dead stems after fire and insect outbreaks. This report includes my research results,
both published and unpublished, on stem decay, as well as those of many of my colleagues in this field.
It deals only with decay in living trees, not in dead stems. Except for some of my research on aspen, all
of my experience is in stands of natural origin. Future harvests, particularly in spruce and pine, will
increasingly be of plantation origin; others will have their origin in unplanted cutovers. Nevertheless, for
the next three or four decades, harvesting will likely continue to be carried out predominantly, or at
least frequently, in natural stands. Furthermore, in determining stem-decay relationships in a stand of a
particular species originating from a plantation and/or cutover, a knowledge of stem-decay relationships
in natural stands is a valuable asset.
This report is concerned only with stem decay and stain, i.e., with internal defects within the
merchantable portion of the stem. The merchantable portion is now considered to start 15 cm above
ground. Readers should bear in mind that in the aforementioned provincewide decay survey of the
1950s, and most other decay studies carried out before 1970, 30 cm above ground was regarded as the
merchantable limit. Hence, in those studies, decay in the butt regions between 15 and 30 cm was
missed, and the total volume of stem decay was slightly underestimated. Decay in the root systems,
generally called root rot, and decay within the stumps, are referred to but are not discussed
quantitatively in this report. Root rot is widespread in Ontario’s forests, and is responsible for
considerable damage in the form of windfall, reduced tree increment and tree mortality (Whitney 1988).
The fungi responsible for root rot can spread from infected to healthy trees via root grafts, root-system
wounds, dead roots, or subterranean strands of fungal material. The decay caused by these fungi can
extend into the basal stem region, although the majority of infections probably do not extend above
stump height. Hence, fungi such as Armillaria mellea (now believed to be mostly A. ostoyae plus other
Armillaria species [Dumas 1988]), one of the most widespread and serious of the decay-causing fungi or
groups of fungi in Ontario’s forests, can have a far greater impact than their incidence as decay within
merchantable stems would indicate.
The scientific names (i.e., Latin binomials) of the various tree species in this report are not used
throughout the text, but are provided in Appendix A. Scientific names of the fungi responsible for stem
decay in Ontario’s forests will neither concern nor interest many readers of this report. However, they
will be important to some, and hence have been included, particularly since common names for many of
the decay-causing fungi either do not exist or are virtually meaningless. No attempt was made to list all
of the fungi known to cause decay in each species; instead, only those fungi responsible for the major
(i.e., most serious) stem-decay problems are included. A more comprehensive list of the occurrence of
fungi in Ontario has been provided by Myren and Davis (1989) for the pines, and by Davis and Myren
(1990) for conifers other than pines; similar reports for hardwood species are being prepared by these
authors.
Unfortunately, most fungi included in this report have undergone at least one name change since the
1940s. Some readers will be familiar with the older but not with the newer name, whereas the reverse
may be true for other readers. Therefore, it is imperative that both names be given. In such cases, the
older name appears first, and is followed within parentheses by the new (proposed or accepted) name.
Because some readers may read only those parts of the report dealing with one or two species, when
the same twice-named fungus caused decays in two or more species it was necessary to repeat this
information under each species. All fungi with two scientific names are listed in Appendix B.
The first sections of this report deal with the general stem-decay problem and opportunities for
reducing it. The remaining sections deal with stem decay in individual tree species. A more-or-less
standard format is used in the latter sections, in which the sequence of topics is roughly as follows: the
relative amount of defect present; the relationship between tree age and stem decay; the pathological
rotation age; the relationship between decay and site, growth rate, diameter, geographic location, etc.;
the relative proportions of trunk and butt decay; the main fungi responsible for decay; a description of
major decays; the entrance courts of decay fungi; external indications of stem decay; problems with
respect to wood utilization; and the avoidance of excessive losses to decay through silvicultural or
management procedures.
Stem Decay: Causes, Processes And Characteristics
“Decay” and “rot” are the terms used to describe wood within the stem of a living tree that has been
noticeably weakened by the breakdown of some or all of its cell walls. Decay or rot occurs in pockets or
columns of all sizes, from tiny pockets little larger than a cubic centimetre to columns that occupy
almost all of the xylem for several metres of stem length. All tree species in Ontario’s forests are
susceptible to stem decay.
Several members of a group of fungi called the Hymenomycetes, which belong to the class
Basidiomycetes, are the cause of most stem decay. They are referred to as decay fungi, and are capable
of degrading and metabolizing cell-wall substances. These fungi frequently pass from cell to cell through
bore holes in the walls, which they form by enzyme action. The subsequent enlargement of the bore
holes results in a gradual, progressive reduction in the mechanical strength of the invaded woody
tissues. In the advanced stage of decay, the wood loses virtually all structural strength.
When decay fungi initially invade stem wood, sometimes there is no visible evidence of infection and
they can be detected only with a microscope or by careful isolation of the fungi in a laboratory. More
frequently, there is a color change in the wood, particularly in deciduous trees, that ranges from slight to
pronounced. However, the discolored wood may remain just as hard and firm as sound wood for a time.
There is a tendency, even among some forest pathologists, to call this discolored wood decay or rot. This
can be very misleading, because there are other types of discoloration in firm wood that are very similar
in appearance but that are not caused by decay fungi. In some tree species, the central core of the stem
is eventually discolored because of the normal aging process and death of the cells. This “true”
heartwood is just as strong as clear, sound wood. In most species, stem wounds or branch stubs that
result in exposure of the xylem to the atmosphere can lead to pronounced discoloration, partly as a
result of the oxidation of certain chemicals.
Microorganisms other than decay fungi, namely bacteria, yeasts and non-decay fungi, can also invade
stem wood and cause discoloration; again, these are more common in deciduous trees. But of all these
types of discoloration, only that caused by decay fungi will eventually weaken (decay) the wood unless,
of course, the other discolored areas are subsequently invaded by decay fungi. All discolored, firm wood
can be used with few or no drawbacks in most manufacturing processes, such as chemical pulping.
Therefore, I recommend that all firm, discolored wood, regardless of type, be referred to in terms of
discoloration or stain. When the softening or weakening of the wood can first be detected, the term
“incipient decay” should be used, to distinguish it from stain and from the very soft, weak wood of the
advanced-decay stage.
Stem decays are frequently classified as either trunk decays (trunk rots) or butt decays (butt rots). Trunk
decays are located in the main and upper portions of the stem, although they sometimes extend down
almost to ground level. Butt decays occur within the basal 2 m or so of the stem. They are generally
widest at or near ground level, and extend upwards in the shape of a cone.
Decay fungi can be divided into two broad classes, called “white rots” and “brown rots”, on the basis of
their effects on wood. The basic difference between the two is that white rots degrade the lignin
component of cell walls, whereas brown rots leave lignin virtually undigested. White-rot fungi degrade
cellulose and hemicelluloses at roughly the same rates, but lignin is usually decomposed at a somewhat
faster rate. Brown-rot fungi degrade and utilize only the cellulose and hemicellulose of the cell wall.
These differences result in decays distinctly different in appearance. White rots are generally yellow or
orange, with a stringy or spongy texture, and in some cases they contain white pockets composed of
almost pure cellulose. Brown rots are pale to medium brown, with a dry, cracked, cubelike appearance,
and when they are in the advanced stage, affected wood can be crumbled between the fingers.
Although two or more Basidiomycetes may invade the stem through a single wound, one of them will, as
a rule, be the most aggressive or most suited to the microenvironment of the colonized wood, and will
inhibit or even eliminate the others. Hence, a decay pocket or column that originated from a wound will
generally have a uniform appearance and characteristics that depend on the identity of the dominant
fungus.
Factors Influencing The Occurrence And Spread Of Decay
Most stem decay originates from the germination of spores, usually air-borne, of decay-causing fungi
after their deposition on suitable host substrates. The exceptions are those cases in which a decay
originates from an already established decay, either by moving up into the stem from the root system or
by moving from one stem to another via stems that are connected at their basal region.
Fungal spores are produced by specialized structures of the fungi called “fruiting bodies” (sporophores).
These can be the familiar hoof-shaped, or inverted bowl-shaped, conks on tree stems or logs, crusts of
matted fungal material on wood surfaces, or, in the case of some butt-decaying fungi, mushrooms
growing on the forest floor. Some sporophores have been found to produce many billions of spores
daily. Because they are so small and light, spores can be carried great distances in the air. To germinate
successfully, they must be carried by air currents (or in some cases by insects or animals) and deposited
on trees of species that they are capable of infecting. However, even then, spore germination will by no
means ensure infection of the host tree, since the hyphae (narrow, tubelike fungal filaments) cannot
penetrate intact bark or living sapwood and soon die unless they happen to be deposited on exposed
and consequently dead sapwood or heartwood.
On living trees, bridges that enable the spores to bypass intact bark and healthy sapwood occur in
branch stubs, dead branches, broken or dead tops, and stem wounds caused by fire, falling trees,
sunscald, cankers, frost cracks, lightning, animals, etc., in which the bark is scraped or knocked off, or
dies and sloughs off with time. But even when spores are deposited in such areas and germinate, the
hyphae have numerous obstacles to overcome before reaching, colonizing, and decaying the stem
heartwood. Many other fungal spores and bacteria are present in the air, and several microorganisms
can be deposited on the same tissue, all competing for the same substrate and nutrients. Bacteria and
non-decaying fungi (usually non-Hymenomycetes) frequently establish themselves first, and cause
discoloration of the tissue. Some of these “pioneer” microorganisms appear to alter the substrate,
making it either more or less suitable for the decay fungi. Some decay-causing Basidiomycetes are
stopped or slowed by pioneer microorganisms, whereas others appear to be dependent on the presence
of certain pioneer species before they can become established.
Apart from the intense and complex interactions among the invading microorganisms, the host tree
itself is by no means passive. Living trees attempt to cover up exposed wood through external closure of
the wound by the formation of callus tissue. However, this is a relatively slow process, far too slow to
prevent massive invasion by microorganisms in all but the tiniest wounds or branch stubs. A second
healing mechanism, internal compartmentalization, is far more effective and allows trees to survive
countless invasions by microorganisms during their lifetime. The process is far too complex to explain
here in detail. Basically, the living parenchyma cells in the vicinity of a wound or branch stub react
chemically and anatomically to form barriers around the wound or stub. This can be regarded as an
attempt to isolate or “compartmentalize” the wound and protect the wood behind the barrier both
from invasion by microorganisms and from further moisture loss. This process involves the production of
substances that inhibit, or are toxic to, the invading microorganisms. Some of these substances plug the
vessels and tracheids as part of the barrier. Many of the parenchyma cells die, the phenolic compounds
that are formed are oxidized, and the barrier zone frequently is considerably discolored and darkened.
The tree has another defense mechanism against microorganisms that succeed in penetrating the series
of protective barriers that form successively towards the stem center. The callus, mentioned earlier, that
develops over exposed wood or branch stubs is composed of wood (produced by the cambium) that has
been stimulated by the nearby wound to form xylem tissue differing markedly from normal stem tissue.
The callus wood has a far higher proportion of living parenchyma cells, other cells have thicker walls,
and there are more of the inhibitory substances mentioned previously. This is a very effective antifungal barrier, and as a result, invading microorganisms and wound- related discolorations are
frequently confined to wood already formed when the stem wound occurred or when the branch died.
Before World War II, it was generally assumed that the majority of stem-decay infections occurred via
branch stubs, simply because they were present on all mature trees and were usually far more
numerous than stem wounds. In the two decades after the war, many intensive stem-decay
investigations were carried out in North America. In most cases, relatively little stem decay appeared to
have originated at branch stubs, whereas stem wounds were increasingly revealed as the main culprit.
This outline of the decay infection process and the defensive reactions of trees help to explain why this
is so. Most branches die from suppression when they are of relatively small diameter. The “wound area”
on the stem associated with a branch stub is seldom larger than 4 to 5 cm2. Consequently, the
protective barriers formed by the living xylem tissue at the base of the dead branch, combined with the
relatively rapid callus closure over small branches that break off flush or nearly flush with the stems, are
more likely than stem wounds to prevent invasion by decay fungi, as stem wounds frequently involve a
much greater wound surface area. In some tolerant hardwoods, dead branch stubs are often associated
with columns of discoloration that can extend into the central core of the stem, but these are very
seldom decayed. The situation is different with dead branches of relatively large diameter. Before dying,
large branches have relatively few living cells, if any, in their central core, so that if a protective barrier
forms in the base of the branch, it is relatively weak and often penetrated by decay fungi. In addition,
branch stubs of large diameter take considerably longer to be completely enclosed by callus.
The sequence of events that leads to the development of an extensive decay column associated with a
stem wound is generally believed to be somewhat as follows. After the wound is inflicted, hundreds,
perhaps thousands, of different microorganisms reach the exposed wood. The majority probably die
with very little or no biological activity. Bacteria, yeasts and molds do best on the dead, somewhat
desiccated, exposed tissue, as they can directly utilize the simpler compounds found there. Slowly,
another group of fungi becomes dominant; these belong to the class Ascomycetes and are capable of
utilizing some of the more complex compounds present. The Ascomycetes are probably the first
organisms to test the tree’s protective barriers, and some are capable of penetrating the barriers by
breaking down and detoxifying the inhibitory compounds. The invaders may even utilize the byproducts
of this breakdown. This barrier penetration triggers an attempt by the tree to form another chemical
barrier, or reaction zone, ahead of the invaders. The interaction between the invading Ascomycetes and
the tree continues, but as the “battle zone” moves inwards, the proportion of living to dead xylem cells
usually decreases steadily, and thus the chemical barriers get progressively weaker. Meanwhile, the
Ascomycetes thrive and inhabit the invaded zone at increasing densities. Despite intensive competition
among themselves for available nutrients, eventually they completely overcome the ability of the tree to
arrest their inward (radial), vertical, and, to a lesser extent, tangential spread. The only persistent barrier
is that between the wood formed before and after wounding.
About this time, the Basidiomycetes are able to compete with the Ascomycetes after detoxification of
the chemical barriers by the latter organisms. Whereas Ascomycetes stain the wood, they cannot attack
the cell walls, and therefore decay does not take place until Basidiomycetes move in. As a rule, one of
the Basidiomycetes eventually dominates the central core of the stem in the vicinity of the wound,
almost to the point of excluding all other microorganisms. A zone of stained wood frequently surrounds
the decay column; this is frequently inhabited by a few of the Ascomycetes and even by some yeasts
and bacteria.
Massive stem decay generally develops from a stem wound only if the wound exposes a relatively large
area of wood, as often occurs with fire scars, severe felling wounds, sun scald, large cankers, and manmade wounds such as blazes or skidding scars. Even in these cases the tree has a chance to prevent or
compartmentalize the decay if it is healthy and vigorous and therefore can react efficiently to wounding
and fungal invasion. Clearly, anything that reduces the vigor of a tree or stand, as happens naturally with
increasing age and competition or as a result of man’s activities (e.g., some types of harvesting
operations, air pollution, fire, etc.), will lower the ability of the tree(s) to fend off the invasion of decaycausing fungi. It is not surprising that in almost all tree species, age is the factor most closely related to
the extent of internal stem decay. Besides becoming less vigorous, trees, as they age, are much more
likely to suffer severe stem wounds (Fig. 1) and to have more large branch stubs, which are the principal
entry points for decay. As stands become overmature the percentage of stem volume decayed may even
decrease, simply because of the progressive removal, through breakage, windfall, and mortality, of the
most extensively decayed individual trees. Relatively poor sites, which result in below-average tree
vigor, will also tend to increase the susceptibility of trees to stem decay.
Figure 1. Stem decay associated with a severe stem wound on aspen. (a) standing tree, (b) felled tree
with extensive advanced decay at the wound.
The inner stem core of mature or overmature trees invaded by decay-causing Basidiomycetes has no
living xylem cells, or very few, above and below the decay column. Therefore, the decay column spreads
mainly vertically. The average annual rate of spread in Ontario is relatively slow, ranging from 3 or 4 to
11 or 12 cm. Decay can continue until the inner stem is completely hollow. Eventually, when decay is
very advanced, many Basidiomycetes produce fruiting bodies (conks, etc.) on the outer surface of the
stem, frequently on branch stubs. Only a few Basidiomyetes produce fruiting bodies on living trees; the
majority do so only after the tree is dead. These fruiting bodies produce spores that are carried by air
currents or by other means to stem wounds or branch stubs on younger trees, and the disease cycle
continues.
Assessing The Extent Of Stem Decay
Because stem decay has such an adverse effect on most utilization practices, some idea, no matter how
rough, of the extent of decay in different stands is helpful in planning harvesting operations. Clearly, the
closer the estimates are to the actual extent of stem decay, the better the chances for efficient
harvesting and utilization. Because there are so few reliable external indicators of stem decay in most
species, in many instances decisions are made to bypass temporarily stands that appear to be relatively
sound and decay-free. Only later is it discovered that, whereas these trees could have been profitably
harvested in the first instance, stem decay has become so extensive that harvesting is now economically
impractical. Major underestimations of the extent of stem decay over a wide area can have a
devastating effect if a mill has been established at considerable expense and it is discovered that
extensive stem decay has greatly reduced the opportunities for profitable operations. On the other
hand, major overestimations of stem decay can result in decisions not to construct mills and/or harvest
in certain regions that could have supported very profitable operations.
From the preceding section on the occurrence of stem decay, it is obvious that stand age, or the
distribution of age classes in the case of uneven-aged stands, is the first parameter to measure when
one is estimating the incidence of stem decay. In Ontario, tables and graphs have been prepared to
show the average relationships between age and decay for most of the major commercial forest species
(Morawski et al. 1958). This publication is now out of print; however, in 1978, the Ontario Ministry of
Natural Resources (OMNR) reproduced these tables (with measurements in metric units) in pocketbook
form for use in the field (Anon. 1978). With these tables, graphs available from the earlier publication,
and a knowledge of stand ages, a rough estimate of percentages of volume culled for different tree
species can be made. If site, soil conditions, tree growth rate, and other stand parameters indicate that
the stand is of below- or above-average vigor, these estimates can be raised or lowered accordingly.
Although visible external indicators of stem decay are rare on living trees, they should certainly be used
to estimate the extent of internal stem decay when they are present. In the few species in which trees
bear conks or other forms of fruiting bodies of stem decay fungi before they die, this is one of the most
reliable indicators of decay. In some cases, the average vertical extents of decay columns above and
below each conk have been studied and reported (Riley and Bier 1936). However, it is dangerous to
place too much faith in fruiting bodies as indicators of decay. Whereas conks are reliable indicators, the
absence of conks in the same tree species does not necessarily mean the absence of decay. Different
decay fungi produce fruiting bodies in association with very different amounts of stem decay. Fungi that
can grow only on patches of dead sapwood may also produce fruiting bodies on a wound or branch
stub; these indicate superficial decay but not internal stem decay. Large branch stubs, broken or dead
tops, stem wounds, or scars that represent callused-over wounds indicate that stem decay could be
present. Attempts have been made to estimate the extent of decay in living trees, or the percentage of
merchantable volume culled because of decay, on the basis of the presence, type, size, severity and
location of external indicators of decay. There are several drawbacks to estimating the extent of stem
decay in a stand solely from external indicators. In many cases, and in virtually all cases for certain tree
species, extensive columns of advanced stem decay are not reflected by any externally visible sign or
symptom. Furthermore, stem abnormalities such as excessive branching, galls and burls are not usually
associated with stem decay. Finally, a stem wound or large branch stub may appear to be a likely source
of extensive stem decay, but unless the tree is felled and dissected, or the wound area is probed in some
way, there is no external indication of the outcome of the battle between the invading microorganisms
and the tree’s protective mechanisms.
The desirability of developing a nondestructive method of detecting decay within the stems of living
trees has been recognized for some time. Increment borers can detect widespread decay, but can miss
pockets that are off-center. Other methods that have been researched include X-ray scanners, ultrasonic
devices, electrical-resistance meters, microwaves and magnetic resonance. Most of these methods can
detect the presence and perhaps even the extent and stage of decay in the vicinity of the portion of
stem tested. However, they are of limited practical value in forest stands because they are expensive,
many are not very mobile, and it is difficult or impossible to get readings at heights above 2 m, where
the decay situation may well be quite different from that below 2 m.
Until a quick, non-destructive method of assessing the extent of stem decay throughout the
merchantable length of a living tree has been developed, the best estimate is still based on the
extrapolation of data obtained from intensively measured, felled trees selected to represent as closely
as possible the stands to which the results are to be applied. To be of the greatest value, data should be
collected, and decay relationships calculated, on the basis of tree and stand age, history, site, diameter
class, height class, and growth rate (as an indication of vigor). Decay or cull factors can then be assigned
to stands for which some or all of those parameters are known. Since the impact of certain stains and
incipient decays frequently depends on utilization practices, all such defects throughout the
merchantable stem should be mapped and described as accurately as possible. Indeed, all internal
defects in addition to decay and stain should be recorded, as well as stem wounds and other external
indicators of decay. Because the extent of stem decay can vary so widely among individual trees, even
within even-aged stands on uniform sites, the accuracy and reliability of the results generally increase
with the number of trees sampled. For the same reason, the results are applicable to extensive stands
but are of limited value in predicting stem decay in only a few trees.
Effects of Decay on Utilization
Most readers of this report who are likely to apply the results will be familiar with how decay and stain
affect their particular utilization procedures. Consequently, this section presents merely a general
overview of the situation. In subsequent sections that deal with individual species, more details will be
presented.
As far as the pulp and paper industry is concerned, the utilization of decayed timber involves several
disadvantages, and no apparent advantages. Because brown-rot fungi decompose the cellulose while
leaving the lignin component of the cell walls virtually untouched, wood that they have decayed should
never be used, even in the incipient stage. The fact that cell walls in decays caused by white-rot fungi
are partially delignified suggests that those fungi may be beneficial in pulping. White rots frequently
produce pulp that differs very little in yield, on a weight basis, from pulp produced from sound wood.
However, the decomposition of the lignin by white-rot fungi is always accompanied by some
decomposition of the cellulose and the hemicelluloses. Consequently, the fibers tend to be shorter and
weaker than normal, even in the case of fungi that cause decays containing white pockets of almost
pure cellulose. The result is pulp of inferior quality. Interest is growing in the development of techniques
for using white-rot fungi or their delignifying enzymes in biological pulping processes. Some of these
biotechnology studies show considerable promise for the future. For example, using mutants of whiterot fungi that have minimal effects on cellulose to remove even small amounts of lignin from wood or
from mechanical pulp reduces the energy required for mechanical refining (Kirk et al. 1983). However,
inclusion of naturally decayed wood almost always has a detrimental effect on the manufacture of pulp
and paper.
The groundwood pulping process appears to be the most seriously affected by the presence of decay.
Stained wood that is as firm and hard as sound wood has little effect on fiber strength, since even if the
stain is of fungal origin, the fungi responsible do not decompose the cell walls. However, staining causes
such losses in brightness that such wood is generally not used by groundwood mills. Decay, even in
incipient stages, causes serious brightness problems and pronounced reductions in groundwood pulp
strength. Groundwood pulp yield also decreases with increasing amounts of decay. Processing problems
as a result of foaming and sticking have also been reported.
Although few studies have been carried out on the relatively new process of thermomechanical pulp
(TMP) production, such pulp appears to be far less seriously affected by decayed wood than is
groundwood pulp. Decays caused by white-rot fungi appear to have little effect on pulp yields or on
brightness. Strength properties are reduced, but far less than in the case of groundwood pulps.
As far as chemical pulps are concerned, the results of different tests do not always agree, probably
because of differences in the methods used, tree species, stages and types of decay, and proportions of
decayed to sound wood. The general consensus appears to be that sulfate (kraft) pulps suffer noticeable
reductions in yield but only moderate reductions in quality when decayed wood caused by white-rot
fungi is used. Sulfite pulps generally show relatively little reduction in yield and moderate-to-slight
reduction in quality; however, appreciable losses in brightness are frequently reported. In both sulfate
and sulfite pulps, strength is reduced because the decay fungi and the chemical pulping processes
combine to shorten the fibers and make them more flexible; tear strength is the property most seriously
affected. Besides causing quality, yield and brightness problems, the use of decayed wood in chemical
pulping processes can result in increased alkali consumption, non-uniform pulping, and increased
recovery-boiler loading. If a decision is made to allow a certain proportion of decayed wood in chemical
pulping, such wood should be mixed as uniformly as possible with sound wood to minimize problems
with cooking, pulp freeness control, and energy consumption.
In lumber manufacturing, reductions in product value and increases in sawmill processing costs are likely
as the amount of decay in logs increases. Decayed material is avoided in veneer manufacture because of
serious product-value reductions and because of the difficulty of holding such material in a lathe. Logs
that contain decay can be used in the manufacture of waferboard, largely because much of the decayed
wood breaks up and is separated out as “fines”.
Other Economic Impacts of Stem Decay
A prerequisite for determining the economic impact of stem decay is some idea of the losses it causes,
either as wood volume rendered unmerchantable or in terms of the dollar value of that wood. Losses in
the form of seedling, tree or stand mortality caused by forest fires or by forest pests can be determined
fairly easily. Losses in the form of stem deformities and reduced increments caused by pests that seldom
or never kill trees can also be determined, albeit with greater difficulty. However, losses from decay
within the stems of living trees are extremely difficult to quantify or put a value on, for several reasons.
For most tree species in Ontario, there are few or no reliable, externally visible signs of internal stem
decay. For reasons already outlined, it is impossible to obtain an accurate assessment of the overall
extent of stem decay in Ontario’s forests and the rate at which that volume changes annually. Even
when estimates based on available knowledge and data are made, other questions arise. Should decay
in overmature stands that are so defective that harvesting is financially impractical, or in mature stands
that are so far away from the mills and so inaccessible that they will never be harvested, be included or
disregarded as irrelevant? Should the annual increase in volume of stem decay in the total accessible
forest resource be considered, or only the decay volume in the average annual resource that is
harvested? In many cases it is not practical to attempt to use the remaining sound wood in logs or trees
that contain considerable decay; consequently, the loss in commercial wood volume is much greater
than the actual volume of decayed wood. Furthermore, wood affected by incipient decays and even by
some types of advanced decay can be used to a limited degree for certain purposes but not for others.
Finally, it is generally assumed that stem decay does not kill trees because the decay fungi do not attack
the phloem or cambium, and seldom the outer sapwood, of the stem. But how safe is this assumption?
When a tree dies, some harmful agent conspicuous at the time of death is usually blamed. It is
reasonable to believe that in some cases this agent could not have caused death if the tree’s vigor had
not been substantially reduced by years or decades of stress involved in attempting to
compartmentalize several decay columns.
Despite all of these reasons why losses attributable to stem-decay fungi are impossible to quantify
accurately, forest pathologists are frequently asked to provide some estimate of overall losses caused by
stem decay, usually on an annual basis. Consequently, there are numerous reports of annual losses
caused by stem decay in various parts of North America (in some cases, values were converted to million
m3 for ease of comparison): United States, 1952, 33 million m3 (Anon. 1958); eastern and southern
United States, 1961(?), 28 million m3 (Hepting and Fowler 1962); Canada, 1965-1966, 24 million m3
(Anon. 1967); Canada, 1976, 25 million m3 (Anon. 1979); British Columbia, 1964-1973, 11 million m3
(Dobie 1976); and Ontario, 1977-1981, 9 million m3 (Gross 1985). Few details are provided in these
reports as to how these figures were calculated. The figures are estimates of annual losses from stem
decay within the total forest resource, and are clearly of considerable magnitude.
After completing the Ontario-wide decay study in the 1950s, referred to in the Introduction, my
provincial colleagues and I calculated annual stem losses in Ontario. However, in contrast with the
above reports, our calculations were confined to losses incurred during harvest operations, and were
based on summaries of the volume of each tree species cut annually in Ontario that were contained in
the 1960, 1961 and 1962 Annual Reports of the Minister of Lands and Forests of Ontario. Both the
designation of ages considered most likely to approximate average harvesting ages for each species and
decay-study data indicating the percentage of total merchantable volume affected by stem decay for
each species at those harvesting ages were used in these calculations; this was carried out in
consultation with senior officers of what was then the Timber Branch, Department of Lands and Forests.
After the decayed volume percentages had been converted to percentages representing volumes culled
in accordance with the Ontario timber-scaling regulations in effect at that time, the volume of annual
harvest that would be culled because of stem decay was calculated. This volume, which was 6.3% of the
annual gross merchantable volume cut, amounted to 620,000 m3.
Since the annual revenues from Crown stumpage charges by species were also available from the
Minister’s Annual Reports, we were able to calculate that the theoretical loss of harvested volume
caused by stem decay represented a loss in revenue of $880,000. Details of all these calculations, with
tables and other supporting information, have been published (Basham and Morawski 1964). As this
paper is no longer in print, the tables and the text that accompanies them have been reproduced in
Appendix C.
Clearly, these figures, 620,000 m3 of culled wood and $880,000 in lost stumpage revenue, are not
particularly meaningful. First of all, they are based on cutting and revenue data that are about 30 years
old. Even if the lost stumpage revenue could be updated and increased to represent the actual mill or
market value of the wood volume lost, it would not mean a great deal. The figure of 6.3% of harvested
timber culled because of stem decay is useful because it has not likely changed appreciably over the
years. However, the wood required to satisfy market or mill demands will usually be obtained,
regardless of the amount of stem decay present in the stands harvested. Hence, there will be no real
loss of stumpage revenue. The real economic impact of stem decay lies in the fact that decay renders
the part of the tree it occupies useless for most purposes, and more trees or stands must be cut to
obtain the required volume of wood for the mill. This raises the cost and lowers the efficiency of logging
operations. Furthermore, it is usually impossible to avoid including some decayed timber in the harvest.
At the mill, it is costly to separate this decayed timber from the sound timber, and some or all of it is
used, with the result that the yield and value of the product are reduced.
The fact that decay is present in all stands and usually increases steadily with age has additional
economic consequences. Mills with a high proportion of stands that reach rotation age at roughly the
same time, or that are in inaccessible areas, may be forced to bypass some of those stands, which in
time become too decadent for profitable harvesting. Areas that support such stands are considered
unproductive and are therefore abandoned until they burn or break up naturally, which may take
several decades. In other areas in which the timber resources are limited or the annual allowable cut is
being used fully, bypassing stands that are marginally defective in favor of relatively sound stands could,
in the long run, effectively reduce the resource base, with serious economic consequences.
In view of the difficulty of assessing the overall economic effect of stem decay in the forest, and the
wide variety of utilization practices and standards, any calculations of decay impact on a national or
provincial basis, or even attempts to quantify the volume of wood lost because of stem decay, are not
particularly meaningful except that they provide rough estimates of the overall seriousness of the stemdecay problem.
Combating Stem Decay
We know how to prevent or minimize stem decay in individual trees. Because some cost is usually
involved, such procedures are generally limited to accessible areas in which the health of each tree is of
some concern (e.g., urban regions, public campsites, etc.). In forest stands or extensive woodlots,
treatment of individual trees is usually not practical, and the elimination or prevention of stem decay is
virtually impossible. However, by using information on the relationships between the occurrence of
stem decay and other factors, losses attributable to decay can to some extent be predicted and avoided,
and the impact of stem decay can be minimized.
Although the prevention of stem decay is unlikely to be the principal factor that governs decisions about
silvicultural and management procedures, forest managers should nevertheless be aware of how those
procedures can minimize decay. As a rule, any treatment that reduces competition and improves tree
vigor will tend to reduce the extent of stem decay. Thinnings and improvement cuts should remove
trees that bear conks or large stem wounds, as well as trees with crooked or malformed trunks. Pruning
branches before they reach a diameter of 2 cm will greatly reduce the chance of their becoming a source
of stem decay. This can be done artificially or naturally (self-pruning), by maintaining a relatively high
stand density while stands are young and the branches are relatively small. The latter should be
followed by a release thinning to increase the growth rate and vigor of the remaining potential crop
trees.
Prevention of stem wounding is an obvious means of minimizing stem decay. Some wounds are
unavoidable, but many of the most serious types are caused by man. In thinning or any harvesting
procedures other than clearcutting, care should be taken that the residual trees are not wounded by the
trees that are felled or by the harvesting machinery. Suddenly exposing trees to the sun’s rays from the
south or west, particularly trees of thin-barked species, can result in sunscald injuries. Felling as little as
is silviculturally necessary in a stand will reduce the risk of decay among residual trees.
Because stem decay is so closely related to the age of a stand, the simplest means of combating it is to
harvest stands before they reach an age at which the extent of decay is likely to become economically
unacceptable. With many species, the volume of stem decay will eventually begin to increase faster than
the volume of sound wood if stands are left uncut. Stands should be harvested before then if serious
losses from decay are to be avoided. The maximum age at which a stand should be cut on this basis is
called the pathological rotation age, and it will vary with the site, general stand vigor, and utilization
practices. Rotation ages are probably very seldom determined exclusively by the progressive
development of stem decay, but in the case of relatively defective, short-lived species, decay should be
seriously considered along with other factors in reaching a decision.
A recent approach to combating stem decay, and one which holds great promise in the future, is the
biological control of stem-decay fungi. A few bacteria and fungi isolated from clear, sound stems of
living trees have been found to be distinctly antagonistic towards decay-causing fungi, both in the
laboratory and when inoculated in standing trees. These organisms appear to do very little, if any, harm
to the tree. Attempts are being made to introduce them into trees by inoculation of seedlings. Strains
are being sought that are particularly antagonistic to decay fungi and will spread systemically from the
seedlings throughout the tree. In this way, it may eventually be possible to produce mature, relatively
decay-resistant trees at reasonably low cost.
Stem Decay In Ontario, By Species
Conifers
White Pine
White pine blister rust and the white pine weevil are generally considered the major pest problems of
white pine. With trees or stands less than 125 years old, this is usually true. However, when stands more
than 125 years old are harvested, stem decay can be an even more serious problem. I am aware of only
one extensive decay study of white pine in or near Ontario in which many trees of different ages were
felled and carefully dissected to determine the extent of decay in each stem. This study was carried out
between 1947 and 1949 by White (1953), who examined 1,012 trees with a minimum DBH of 15 cm in
overmature, mature and younger stands. White’s results indicate that until trees are in the 101- to 120year age class, white pine stems are fairly sound, and that decay is certainly not a problem in trees less
than 100 years old (Table 1). However, in stands between 120 and 200 years old, from 14 to 17% of the
stem volume is composed of decay or stain (although White found relatively little stain). The 33% figure
in Table 1 for trees in the 201- to 220-year age class is suspect because of the small number of trees (8)
sampled. Although decay increased dramatically after age 120, because of rapid tree growth and the
accumulation of sound wood for the next few decades, White suggested that stands could be left until
trees entered the 160- to 170-year age class before stem decay would have a serious economic impact
(Fig. 2).
Table 1. Occurrence of decay and stain in the stems of 1,012 white pine in Ontario. Based on data from
Table 5 in White (1953). Trees were in stands in the Temagami Lake and Ottawa Valley regions.
Age class
No. of Avg. stem
Avg. decay and Stem vol.
(years) trees
vol. (dm3)
stain vol. (dm3) defective (%)
41-60 113
303.0 8.50
2.6
61-80 490
371.0 11.33 3.0
81-100
51
484.3 16.99 3.5
101-120
10
393.6 28.32 7.1
121-140
57
909.1 158.59 17.5
141-160
120
1367.9 240.72 17.6
161-180
110
1821.0 266.21 14.6
181-200
53
2347.7 345.50 14.7
201-220
8
2449.7 809.95 33.1
Figure 2. Average total volume, decay volume, and net volume of white pine stems in relation to tree
age. Volume-age data obtained from curves in White’s (1953) figure 5.
White pine (and red pine) were not included in the provincewide decay survey of the 1950s referred to
in the Introduction, because they were considered too valuable to sacrifice the number of trees that
would be required to provide reliable estimates of decay relationships. I suspect that this explains, to
some extent, why no other white pine decay studies have been carried out in or near Ontario. The only
other detailed examination of white pine stem decay that I am aware of involved trees killed in the vast
Mississagi fire between Blind River and Chapleau, Ontario in 1948. Between 1950 and 1953, 156 killed
white pine trees in 10 stands from 100 to 185 km north of Blind River were felled to study the rate of
development of sap stain and sap rot in the dead stems (Basham 1958a). The occurrence and extent of
decay in heartwood, almost all of which would have been present before the death of the trees, were
also recorded. All of the trees were in the 140- to 160-year age class, and an average of 14.1% of the
stem volume was composed of decay or stain. (Again, this included very little stain.) These results are
comparable with those obtained by White (1953) for this age class in the Lake Temagami and Ottawa
Valley areas. However, the Mississagi white pine at this age had an average merchantable volume of
1.05 m3 in comparison with 1.37 m3 in White’s study. This suggests that a somewhat-younger
pathological rotation age than White’s recommended 160 to 170 years may apply in the northern
Algoma region of Ontario.
White’s study revealed that there was no relationship between tree diameter and the extent of decay
within single age classes of white pine. However, when trees in even-aged stands were divided into fastgrowing and slow-growing groups (trees with average growth rates were excluded), both the percentage
of trees with stem decay and the percentage of stem volume decayed were greater in the slow-growing
trees.
Trunk decay was far more widespread than butt decay, and accounted for 87.6% of the total stem-decay
volume. Approximately 85% of the total decay was caused by Fomes pini (renamed Phellinus pini [Fig.
3]) (White1953). This fungus accounted for all of the trunk rot in white pine, and was occasionally found
in the butt region. It belongs to the white-rot group of fungi; in the advanced stage, the decay consists
of numerous spindle-shaped pockets or cavities parallel to the wood’s grain, separated by fairly firm
reddish-stained wood. These pockets are frequently filled with soft, white masses of almost pure
cellulose (Fig. 3). The remainder of the decay was primarily butt decay caused by five or six species of
fungi. Yellow-orange butt decays caused by white-rot fungi, with a soft, stringy texture, were somewhat
more common than the brown, cubical butt rots caused by brown-rot fungi. These butt decays occupied
much of the central stem region at stump height but seldom extended more than 2 to 2.5 m above that
height.
Figure 3. White pine stem decay caused by Fomes pini (Phellinus pini). (a) transverse section of
advanced decay, (b) closeup of radial section, showing pockets of cellulose in decayed wood.
In a later report, White (1960) stated that F. pini frequently enters white pine stems through leaders
killed by the white pine weevil. Others have found evidence that as much as 80% of F. pini stem decay
has its origin in weevil injuries (Ostrander and Foster 1957; Brace 1971). A study of weevil-damaged
white pine, roughly 37 years old, in a plantation near Thessalon, Ontario, revealed no evidence of decay
associated with leaders killed 17 to 20 years earlier (Basham 1971). However, Brace noted that although
very little decay occurs until 30 years after weevil injury, thereafter it increases rapidly. In well
established F. pini infections of white pine in northern New York state, the average annual vertical
spread of decay columns was 25 cm (Silverborg and Larsen 1967). In a study on the effects of logging
wounds on residual white pine stems during a partial cutting to release pole-sized trees, F. pini decay
was found associated with one skidder gouge wound (Whitney and Brace 1979). Although very little
stem decay was associated with all wounds examined 5 years after logging, the presence of decay fungi
in the exposed wood of felling scrapes, skidder scrapes and gouges, and broken tops suggests that such
logging wounds could have serious consequences as far as decay is concerned when the trees reach
harvestable age.
Since F. pini seldom forms sporophores on the stems of living white pine, trees that appear healthy may
have extensive trunk decay. The rare occurrence of F. pini conks, irregular brownish growths usually
shaped somewhat like brackets or hooves, indicates extensive decay above and below the conks. Other
external indicators of decay are white pine weevil injuries in the form of crooks, swollen or punky knots,
bleeding branch stubs, large woodpecker holes, and any other noticeable stem wounds or scars. One of
the fungi that causes a brown, cubical butt rot, Polyporus schweinitzii (renamed Phaeolus schweinitzii),
may produce conks at the base of infected trees or on the ground nearby. These are thin, bracketshaped protrusions with velvety upper surfaces when fresh.
In the management of white pine, any steps that can be taken to minimize weevil damage and stem
wounds will promote healthier, less decadent stands. In any case, serious decay losses are unlikely if
trees are cut before they reach 120 to 130 years of age.
Red Pine
In Minnesota, red pine has long been considered one of the most disease- and insect-resistant trees in
natural stands (Eyre and Zehngraff 1948). The same is true in Ontario and, largely on the basis of logging
and sawmill experience, it is generally regarded as virtually free of stem decay. For this reason, and
because of the relatively high value of the species, no extensive red pine stem-decay studies have been
carried out in or near Ontario.
The only quantitative data available on red pine stem decay are those collected in the study of the rate
of deterioration of fire-killed jack pine, red pine, and white pine trees in the Mississagi region between
Blind River and Chapleau, Ontario, which was discussed in the section on white pine. In all, 462 red pine
trees from six stands located roughly 100 km north of Blind River were felled, and the stems were
dissected to reveal the extent of sap stain and sap rot (Basham 1958a). The occurrence and extent of
heartwood decay, almost all of which would have been present before the trees died, were also
recorded. All of the trees were in the 141- to 160-year age class. An average of 1.0% of the
merchantable stem volume of these trees was recorded as decayed or stained (very little of this was
stained). This can be compared with the 14.1% figure obtained for white pine of a similar age class in
this study, and confirms the widely held opinion that red pine stems are relatively free of decay. Stem
decay can probably be safely ignored in determining rotation or harvesting ages for red pine stands.
It is of interest to note that whereas only 12.4% of the stem decay in white pine was in the butt region
of the stem (White 1953), 75.0% of stem decay in red pine was butt decay (Basham 1958a). In the trees
sampled in White’s white pine decay study and in the Mississagi fire-killed pine study, butt decay in
mature (141- to 160-year-old) trees was only about twice as common in white pine as in red pine. The
main difference was in trunk decay, which was rarely encountered in red pine.
The fungus responsible for the most stem decay in red pine is Polyporus tomentosus (renamed Inonotus
tomentosus). This fungus causes a white-pocket butt decay very similar in appearance to the decay
caused by Fomes pini (renamed Phellinus pini). For a description of this decay, refer to the previous
section on white pine. The brown-rot fungus Polyporus schweinitzii (renamed Phaeolus schweinitzii)
causes a brown, cubical butt decay, but is only about one-third as common as P. tomentosus. The third
most common cause of stem decay is F. pini, which is responsible for the extremely limited amount of
trunk decay found in red pine. A very small amount of yellow-orange, stringy butt decay is caused
primarily by two other fungi.
Because most stem decay in red pine occurs in the butt region of the stem, one should concentrate on
this region when looking for external indications of decay. Besides basal scars, the presence of fruiting
bodies of the fungi responsible for butt decay, either on the stems or growing on the ground nearby, are
the most reliable signs. Polyporus tomentosus fruiting bodies appear annually, mostly in August,
September and October. They occur on the base of the stem as bracket-shaped protrusions, where they
are tan to dark brown, often with pronounced white margins, and on the ground near the tree as
shallow, funnel-shaped sporophores on short stalks, of the same color as those growing on the tree but
usually with a somewhat narrower whitish margin (Whitney 1977). Fruiting bodies of P. schweinitzii may
also be present; these are described in the previous section on white pine. Regardless of the age at
which stands are cut, it is improbable that stem decay in red pine will have a serious economic impact.
Jack Pine
Jack pine is sometimes regarded as a relatively decadent tree species. This reputation is undeserved,
and is based for the most part on operations carried out in overmature stands more than 120 to 130
years old, in which stem decay can be extensive. Only black spruce was sampled in greater numbers
than jack pine in the provincewide decay survey of the 1950s. Table 2 shows the relationship between
age class and the percentage of merchantable stem volume decayed in 4,287 jack pine sampled
throughout the Boreal Forest Region of Ontario. Comparing the impact of stem decay in jack pine with
that in white pine is difficult because white pine is a much longer-lived and faster-growing species than
jack pine. However, if one assumes an average desirable harvesting age of 80 to 90 years for jack pine
and 120 to 130 years for white pine, trees at roughly the same stage of maturity can be compared. From
Tables 1 and 2 it can be seen that, at these ages, roughly five times as much stem decay, on a
percentage-volume basis, can be expected in white pine as in jack pine. Table 2 and Figure 4 show
clearly that, beyond age 100, stem decay in jack pine increases rapidly. Under average conditions in the
Boreal Forest Region of Ontario, it is recommended that jack pine stands be left no longer than 100 to
105 years if serious losses from stem decay are to be avoided. However, it will be shown later that this
pathological rotation age should be lowered or raised somewhat depending on the location of the trees
within the Boreal Forest Region and on site and soil conditions.
Table 2. Occurrence of decay and stain in the stems of 4,287 jack pine sampled in the Boreal Forest
Region of Ontario. Based on trees examined as part of the federal-provincial decay survey of the 1950s.
Trees were in stands throughout the Boreal Forest Region.
Avg.
Avg. decay
Stem vol.
Stem vol.
Age class
No. of merch. and stain
as advanced
defective
(years) trees
vol. (dm3)
vol. (dm3)
decay (%)
(%)
21-40 275
54.8
0.07
0.0
0.1
41-60 533
95.9
0.88
0.1
0.9
61-80 930
202.9 3.20
0.4
1.6
81-100
1,073 265.4 9.59
101-120
678
1.1
393.0 40.18 3.0
3.6
10.2
121-140
560
503.8 80.21 4.7
15.9
141-160
129
586.6 144.37 7.6
24.6
161+
725.3 262.31 23.0
109
36.2
Figure 4. Average total merchantable stem volume, volume culled as a result of decay, and net volume
of jack pine in relation to tree age. Volume-age data obtained from curves in Morawski et al.’s (1958)
figure 8, courtesy of the Ontario Ministry of Natural Resources.
Two other investigations of stem decay in jack pine were carried out, both in the Lake States before
World War II. Although detailed results are not presented, Weir (1915) reported that, on dry pine
barrens, “jack pine reaches its normal age without much defect in the wood... although exceptionally old
trees of 90 years and more frequently show considerable decay.” He also stated that, in mixed stands,
Fomes pini (renamed Phellinus pini) “causes considerable heart-rot in trees of 60 years and older. In
general, however, this fungus is in negligible quantities.” Weir concluded that stem decay fungi “... do
not produce any appreciable decay till after the tree reaches its period of decline”, which he placed at
approximately 60 to 80 years. In another study, carried out in Michigan, Watson (1937) made increment
borings in 2,000 jack pine trees and found evidence of stem decay in roughly 25% of them. There was a
distinct relationship between age and decay, but decay was more than twice as common in fire-scarred
trees as in trees with no fire scars (Watson 1937). Watson recommended that rotations should be 10 to
20 years shorter in jack pine stands in which light surface fires have occurred repeatedly.
The amount of stem decay in jack pine in the Boreal Forest Region of Ontario was strongly related to
tree growth rate, which in turn was closely linked to site: the drier the site, the slower the growth rate
(Morawski et al. 1958; Basham 1967). For similar age classes, stands more than 80 years old had the
most decay on sites with soil moisture regime 0 (very dry) and the least on sites with soil moisture
regime 2 or 3 (moderately fresh) (Table 3 and Fig. 5). Furthermore, in stands on moisture regime 0 sites,
57.9% of stem decay was in the advanced stage; on moisture regime 1 sites, advanced decay was 56.6%
of the total, and on moisture regime 2 to 3 sites, only 43.1% of stem decay was in the more serious
advanced form. Although the slower-growing trees tended to have a higher percentage of stem volume
decayed than the faster-growing trees within stands, each on fairly uniform sites, this difference was not
statistically significant. Analysis-of-variance calculations indicated that soil moisture regime was
significantly related to the percentage of stem volume decayed in jack pine in Ontario (Basham 1967). In
Ontario and in the Lake States, the fact that jack pine grows more slowly, on average, on very dry sandplain sites with relatively deep water tables than on less dry sites has been known for some time (Weir
1915; Rudolf 1958; Chrosciewicz 1963; Benzie 1977). In the more than 4,000 trees sampled in Ontario in
the provincewide decay survey, the fastest growth occurred on sites with soil moisture regimes 3 and 2,
followed by regimes 1 and 0, in that order. Since growth rate is largely a reflection of tree vigor, this
relationship suggests that site may be related to the amount of stem decay in jack pine at least partly
because of its effect on tree vigor.
Figure 5. Average percentage of merchantable volume culled as a result of decay, in relation to tree age,
for jack pine growing on three different sites in Ontario. Soil moisture regimes within parentheses.
Percentage-age data obtained from curves in Morawski et al.’s (1958) figure 11, courtesy of the Ontario
Ministry of Natural Resources.
Table 3. Relationship between soil moisture regime, age and stem decay in 4,034 jack pine in the Boreal
Forest Region of Ontario (curved values). Trees sampled on sites with moisture regimes 4 and 5 and
trees more than 160 years old (253 trees) constituted samples that were too small to show relationships
and are not included.
Soil
Avg.
moisture
Stem decay
tree age
in advanced
Merch. stem vol. defective (%) by age class (years)
regime (years) stage (%)
41-60 61-80 81-100 101-120
0 (dry) 82
0.9
1.6
5.2
12.0
20.1
26.2
56.6
0.3
1.3
3.7
7.7
13.6
23.9
43.1
1.1
1.6
2.3
4.1
10.0
19.7
57.9
1 (moderately 93
121-140
141-160
fresh)
2-3 (fresh)
97
An even more statistically significant relationship than that between site and the amount of stem decay
was found between the geographical location within the Boreal Forest Region and the amount of stem
decay in jack pine (Basham 1967). The sample plots containing significant numbers of jack pine were
divided into three groups on the basis of their location. Northwestern Ontario, that part of the province
west of a line running north from Thunder Bay, was roughly the same as the present Northwestern
Region of OMNR. A total of 1,612 jack pine, with an average age of 91 years, was sampled there. Northcentral Ontario, from northwestern Ontario to a line running north from Sault Ste. Marie, is roughly the
same as OMNR’s present North Central Region. In the decay survey, 1,294 trees with an average age of
91 years were sampled there. The area from north-central Ontario east to the Quebec border, i.e.,
northeastern Ontario, approximates OMNR’s Northern Region. There, 1,381 jack pine, with an average
age of 86 years, were sampled. In each age class from 61-80 to 120-160 years, two to three times as
much decay was present in the trees sampled in northwestern Ontario as in trees sampled in
northeastern Ontario. Jack pine in north-central Ontario were consistently more defective than
northeastern jack pine and less defective than northwestern jack pine (Fig. 6). In addition to having
significantly less stem decay on a percentage-volume basis than trees in the other two regions, jack pine
in northeastern Ontario had the smallest proportion of stem decay in the more serious advanced stage.
Figure 6. Average percentage of merchantable volume decayed, in relation to tree age, for jack pine
growing in three regions of Ontario. Percentage-age data obtained from curves in Basham’s (1967)
figure 2.
Although many possible reasons have been discussed (Basham 1967), no satisfactory explanation has
been given for the significantly different levels of stem decay in jack pine in the three zones of the
Boreal Forest Region. Soil moisture-regime differences were suspected, as trees from regimes 2 and 3
were sampled more frequently, and from regime 0 less frequently, in northeastern Ontario than in
north-central or northwestern Ontario. However, analyses of variance indicated that, when site was
eliminated as a variable, differences in the extent of stem decay among the three regions remained
statistically significant.
In view of the significant effects of soil moisture regime and of geographic location on the occurrence of
stem decay in jack pine, it is clear that modifications are required in the recommendation made earlier
that jack pine stands be harvested no later than age 100-105 if serious losses from stem decay are to be
avoided. It is probably safe to leave jack pine stands growing on sites with any soil moisture regime
other than 0 in northeastern Ontario until age 120, whereas in northwestern Ontario, stands on sites
with soil moisture regime 0 are likely to develop serious stem decay problems after age 90.
Trunk decay in the 4,287 jack pine sampled in the Ontario decay survey accounted for 80.9% of the total
stem-decay volume; the remainder was butt decay. This can be compared with 87.6% for white pine and
25.0% for red pine. As in the two other pines, very little stain (firm, discolored wood) was found. In all
age classes up to 160 years, incipient decay was slightly more common than advanced decay; in trees
more than 160 years old, almost all stem decay was in the advanced stage. Two fungi, Fomes pini and
Peniophora pseudopini (formerly named Stereum pint), were responsible for all but 2.5% of the decay
volume (Fig. 7). Both fungi cause trunk decay primarily, although both were also associated with some
butt decay in this study. Most of the remaining 2.5% of the decay was butt decay caused by Polyporus
tomentosus (renamed Inonotus tomentosus) and Corticium galactinum (renamed Scytinostroma
galactinum). Almost all of the advanced decay was white pocket rot caused by F. pini and P. tomentosus,
which are described in detail in the section on white pine. Incipient decay was slightly softened
(weakened) wood, predominantly red but ranging from light orangey-pink to brownish-red. About 60%
of this incipient decay was caused by F. pini, the remainder by P. pseudopini, which belongs to the
white-rot group of fungi and rarely causes advanced decay. A relatively small number of jack pine were
infected with white pocket or yellow stringy butt decays, caused mainly by P. tomentosus and C.
galactinum, respectively (both white-rot fungi). Very few trees that were sampled had brown cubical
butt decay. Polyporus schweinitzii (renamed Phaeolus schweinitzii), a brown-rot fungus reported to be
one of the major causes of stem decay in jack pine in the Lake States (Weir 1915), was isolated only
from four of the 4,287 trees.
Figure 7. Jack pine stem decays. Transverse stem sections showing (a) advanced decay caused by Fomes
pini (Phellinus pini), and (b) incipient stem decay caused by Peniophora pseudopini (Stereum pini).
Fomes pini, by far the major cause of advanced decay in jack pine, appears to enter the trunk through
stem wounds such as felling or fire scars, through rust cankers, or through dead or broken tops, but
seldom through dead branches (Basham 1975). The fungus was not found entering broken tops 8 years
after a severe ice storm that occurred near Chapleau, Ontario, in May of 1960 (Basham 1971). In this
case, tree tops had been broken off at diameters ranging from 2.5 to 9 cm, and a light-red stain that
extended down about 40 cm into the stem was associated with trees examined 6 to 8 years after the
damage. No decay fungi were isolated from the stain; however, the results of other studies indicate
that, had the tops been broken off in late fall or winter, decay would probably have occurred (Davidson
and Etheridge 1963). Peniophora pseudopini is an occasional invader by way of dead branch stubs
(Basham 1975), but the majority of infections probably originate at stem wounds. The butt-decay fungi,
including P. tomentosus and C. galactinum, enter the basal stem regions from infected root systems or
through basal stem wounds such as fire scars.
There are few reliable external indications of stem decay in living jack pine. Fruiting bodies of F. pini and
P. tomentosus, described in the sections on white pine and red pine, respectively, occur very rarely, and
visible fruiting bodies of P. pseudopini and C. galactinum almost never occur. Stem wounds such as fire
scars, felling scars, rust cankers (particularly those of the sweetfern rust, Cronartium comptoniae), and
broken tops are the most reliable signs that some internal stem decay is probably present.
Except in the groundwood process, stem decay in jack pine is not a serious problem for the pulpwood
industry. Because stained wood causes brightness losses and incipient decay causes some losses in yield
in groundwood pulp, mills employing the groundwood process should use relatively short rotations on
the poorer sites (such as those with soil moisture regimes of 0), on which some stain and even a small
amount of incipient decay can occur in stands as young as 40 years. As far as chemical pulps are
concerned, stem decay is not a serious problem, as the two fungi responsible for trunk decay both
belong to the white-rot group and cause only some delignification. Furthermore, at customary rotation
ages for jack pine, virtually all the decay they cause is in the incipient stage and seldom amounts to
more than 3% of the merchantable volume. For sawlog production, dry sites (soil moisture regime 0)
should be avoided if possible because of the slower growth of the trees and the more rapid
development of stem decay on such sites.
As mentioned earlier, to avoid significant losses to stem decay, jack pine stands should be harvested no
later than between 90 and 120 years of age, depending on the site and the region of the province.
Regardless of how the harvested trees are utilized, stem decay will have less impact if young stands are
sufficiently dense to promote good self-pruning, and if stands are subsequently protected as much as
possible from stem wounds such as fire scars, felling scars, rust cankers, and broken tops.
Black Spruce
In general, black spruce is second only to red pine among the commercial forest tree species of Ontario
in having the lowest percentage of its merchantable stem volume affected by decay and stain. Only 3.0%
of the merchantable volume of the 6,269 black spruce examined in the Boreal Forest Region of Ontario
in the decay survey of the 1950s was in the form of decay or stain. Unlike in other species, the
percentage of defective stem volume in black spruce does not increase with age up to the oldest age
classes. Instead, defect peaks at ages 121 to 160 and then begins a steady decrease (Table 4). This is
contrary to the accepted theory that the number of entrance courts for decay fungi tends to increase as
trees age, while existing decay pockets expand and tree growth tends to slow down; for these reasons,
decay as a percentage of tree volume should increase continually. Black spruce does not follow this
general pattern for two reasons: first, there is a very strong relationship between site (as expressed by
soil moisture regime) and stem decay, and second, a high proportion of advanced decay in black spruce
occurs in the form of butt decay. Indeed, ages at which stem decay becomes serious cannot be
discussed without these two factors being considered first.
Table 4. Occurrence of decay and stain in the stems of 6,269 black spruce sampled in the Boreal Forest
Region of Ontario. Based on trees examined as part of the federal-provincial decay survey of the 1950s.
Trees were in stands throughout the Boreal Forest Region.
Avg.
Avg. decay
Stem volume as
Stem volume
Age class
No. of merch. and stain
advanced decay
(years) trees
vol. (dm3)
vol. (dm3)
(%)
21-40 24
13.1
0.00
0.0
0.0
41-60 383
48.0
0.62
0.3
1.3
61-80 1,036 71.3
0.72
0.4
1.0
81-100
1,284 85.1
1.01
0.7
1.2
101-120
1,421 107.8 2.68
1.3
2.5
121-140
1,156 119.2 5.61
2.0
4.7
141-160
582
146.5 6.31
2.1
4.3
161-180
254
141.7 5.39
1.2
3.8
181-200
80
129.4 5.04
1.7
3.9
201-220
38
121.2 1.58
1.1
1.3
221+
122.9 3.70
11
2.8
defective
(%)
3.0
Butt decay accounted for 58.2% of the stem-decay volume and 71.8% of the advanced stem decay in
black spruce (Basham and Morawski 1964). Had the 30-cm stumps been examined and included, these
percentages would have been higher, as the vast majority of butt decays are upward extensions of
extensive root-system decays. In a survey of the root systems of 570 black spruce in northwestern
Ontario, Whitney (1976) found root decay in 530 (93%) of them. Black spruce has a relatively shallow
root system (Vincent 1965). As black spruce age, more and more of the infected root systems are
subject to advanced decay, more roots die, and the trees with the most extensive decay in the root
system and butt regions are uprooted or sustain wind breakage. Hence, as stands become overmature,
the majority of trees that are eliminated in this way are those with relatively extensive stem decay, and
the overall defectiveness of the remaining stand can actually decrease with age.
The strong relationships between site (soil moisture regime) and the incidence of stem decay in black
spruce, as well as tree growth rate and longevity, provide additional explanations for the unusual
relationship between age and extent of decay in this species. Statistical analysis (ANOVA) conducted on
the 6,269-tree sample from the Boreal Forest showed that both age and soil moisture regime were very
significantly (P<0.01) related to the extent of stem decay in black spruce, but that the extent of decay
was much more strongly related to moisture regime than to age (Basham 1973b). This is not surprising
for a species in which such a high proportion of stem decay in the butt region originates as root rot,
since the fungi responsible for such decays are primarily subterranean organisms. A greater proportion
of the merchantable volume of black spruce stems was decayed on the drier sites than on the wetter
sites (Fig. 8). Except for borderline cases, black spruce within the 6,269-tree sample were separated into
two groups, those on upland, relatively well drained dry-to-fresh sites, and those on lowland, moist-towet sites with somewhat impaired drainage. After 80 years of age, considerably more decay, primarily
butt decay, was found on the upland sites than on the lowland sites (Morawski et al. 1958). Similar
relationships have been reported in the Lake States (LeBarron 1948; Heinselman 1957; Johnston 1977).
In northwestern Ontario, decay within the root systems of black spruce was far more extensive on drier
(moisture regime 0 to 3) sites than on wetter (moisture regimes 4 to 8) sites, with the least decay found
on wet (moisture regimes 7 and 8) sites (Whitney 1976). Black spruce grows faster in Ontario on upland
sites with predominantly mineral soils than on lowland sites with organic soils (Vincent 1965; Arnup et
al. 1988), a relationship that held true for the black spruce sampled in the decay survey (Morawski et al.
1958; Basham 1973b). In the cull survey, an attempt was made to select stands for sample plots that
were representative of all sites, cover types, and age classes for each species in all regions of Ontario. Of
the 6,269 black spruce sampled, the majority of trees older than 150 years were on lowland sites on
which the incidence of stem decay was much lower than on upland sites. This is perhaps the principal
explanation for the unusual decrease in the extent of stem decay with age in the older black spruce age
classes.
Figure 8. Average percentage of merchantable volume of decayed, in relation to tree age, in black
spruce growing on three different sites in Ontario. Soil moisture regimes are within parentheses.
Percentage-age data were obtained from curves in Basham’s (1973b) figure 6.
On wetter lowland sites with somewhat impaired drainage, stem decay is seldom a serious problem in
black spruce. Because of its slower growth and greater longevity on such sites, rotation ages are
necessarily long but it is highly unlikely that more than 5% of stem volume in stands, regardless of age,
would ever be decayed. On well-drained upland sites in Ontario, on the other hand, Whitney (1976)
stated that “more than one-third of the volume of average upland black spruce stands 75 years of age,
was lost because of root rot”, primarily as a result of windfall and mortality. Fortunately, faster growth
on such sites compensates for these losses to some extent; in many cases, trees reach merchantable
pulpwood size before they reach that age.
Within soil-moisture-regime groups in the Boreal Forest of Ontario (7 and 8 = wet, 4 to 6 = moist, and 0
to 3 = dry-fresh), it was found that black spruce trees with average diameter growth rates greater than
the stand average had greater-than-average amounts of stem decay, whereas trees with below-average
diameter growth rates had lower-than-average amounts of decay (Basham 1973b).
Advanced, soft decay accounted for roughly two-thirds of all decay found in 6,269 black spruce (Basham
and Morawski 1964). The predominance of decay in the butt region rather than in the trunk has already
been pointed out. The principal organisms causing butt decay in black spruce in Ontario are Fomes pini
(renamed Phellinus pini) and Polyporus tomentosus (renamed Inonotus tomentosus), which are
responsible for white pocket decay (Fig. 9), and Corticium galactinum (renamed Scytinostroma
galactinum), which causes a yellow stringy decay. Fomes pini is the principal cause of the less common
trunk decay, but, over all, is associated with more stem decay in black spruce than any other fungus in
Ontario (Basham and Morawski 1964). In an examination of root systems and 30-cm stumps of 570 black
spruce in northwestern Ontario, Whitney (1978) found Armillaria mellea (now believed to be mostly A.
ostoyae) to be the principal cause of decay. This fungus was rarely isolated above the 30-cm stump
height in black spruce in the provincewide decay survey, a reflection of the fact that although Armillaria
is the primary cause of root decay in black spruce in the Boreal Forest Region of Ontario, it seldom
extends into merchantable stems. Appreciable amounts of a reddish trunk decay in black spruce caused
by Stereum sanguinolentum: (renamed Haematostereum sanguinolentum) have been reported in the
Prairie provinces (Whitney and Denyer 1970), Quebec (Lavallée 1965), and the Lake States (Lorenz and
Christensen 1937). Very few infections caused by this fungus in Ontario were found in the decay survey
of the 1950s (Basham and Morawski 1964). Brown cubical butt decays are rare in Ontario; of those
encountered in the decay survey, most were caused by the brown-rot fungus Coniophora puteana.
Figure 9. Black spruce stem decays. (a) transverse and radial views of incipient Fomes pini (Phellinus
pini) decay, (b) transverse section of advanced F. pini decay, (c) radial closeup view of advanced decay
caused by Polyporus tomentosus (Inonotus tomentosus).
Some 300 stem wounds on 190 black spruce in Quebec were examined as possible entry points for trunk
decay (Lavallée 1965). Broken tops were found to be the most common point of entry, followed by
felling wounds. Branch stubs were of minor importance. Fomes pini was most frequently isolated from
stem decay associated with the wounds, followed by S. sanguinolentum. In Ontario, F. pini was rarely
found in black spruce branch stubs (Basham 1973c), and it is presumed to enter mainly through stem
wounds of other kinds. Although F. pini was the fungus most frequently associated with butt decay in
black spruce in Ontario, it differed from the other butt-decay fungi in that, in most cases, it extended
downwards into the butt region from higher entry points. The other butt-decay fungi (P. tomentosus, C.
galactinum, etc.) frequently extend upwards into the butt region after infection of the root system. Basal
stem wounds such as fire scars provide exceptions to these rules and permit entry of both F. pini and
the root-decay fungi, and result in butt decay.
Reliable external indications of internal stem decay in living black spruce are very rare. Apart from
fruiting bodies of P. tomentosus in late summer and early fall (described in the section on red pine),
fruiting bodies of decay-causing fungi are seldom present. Broken tops, felling scars, and fire scars,
unless they are relatively recent, are indications that stem decay has probably formed. However, it
should be remembered that the most serious kind of decay in black spruce, root and stump decay, is
completely hidden for the most part (Whitney 1988).
Practically all stem decay in black spruce is caused by fungi that belong to the white-rot group, so that in
the incipient stage of decay, at least, the wood can be used for chemical pulps with little harmful effect.
Most butt decays, particularly those that originated as root rots, have relatively short incipient stages
and, at stump height, frequently appear as extensive advanced decay. However, these decays seldom
extend more than 1 m above ground and can be avoided by “jump butting” and removing the
lowermost 0.5 to 1 m.
Polyporus tomentosus root rot and butt decay of black spruce can, under certain circumstances, become
exceptionally heavy and cause serious losses in the form of stand openings as a result of mortality and
windthrow. This condition can occur on acidic soils low in nutrients and in moisture-holding capacity,
and where the rooting depth is restricted by shallow or compact soils (Whitney 1977). In such stands,
Whitney recommended clearcutting and conversion of the stand to less susceptible species such as
pines, balsam fir, or hardwoods. The occurrence of root rot can be minimized by taking care that
residual trees are not severely wounded during partial cutting with large multi-operation machinery, by
exposing buried, infected, dead material during site preparation, and by removing as much dead
material as possible from the site (Whitney 1988). Upland sites should be harvested before lowland sites
where age classes are the same or similar, as mentioned earlier. Rotation ages of 50 to 60 years on
sandy upland sites, and 70 to 80 years on finer-textured upland soils, have been recommended for black
spruce to avoid root-rot and butt-decay losses (Whitney 1979). Because faster growth in black spruce is
frequently associated with more stem decay (Basham 1973b), procedures to accelerate the growth rate
of black spruce, such as fertilization or site improvement by drainage, may well raise productivity but are
also liable to increase the incidence of stem and root decay appreciably.
White Spruce
The percentage of merchantable stem volume affected by decay or stain, by age class, in the 564 white
spruce examined in the provincewide decay survey of the 1950s is shown in Table 5. A comparison of
this table the older age classes been sampled, the incidence of stem decay would have negligible effects
on the selection of rotation ages for either pulpwood or lumber.
Table 5. Occurrence of decay and stain in the stems of 564 white spruce sampled in Ontario. Based on
trees examined as part of the federal-provincial decay survey of the 1950s. Of the 564 trees, 481 were in
the Boreal Forest Region and 83 were in the Great Lakes-St. Lawrence Forest Region.
Age class
No. of Avg. merch.
Avg. decay and Stem volume
(years) trees
vol. (dm3)
stain vol. (dm3) defective (%)
41-60 93
78.7
0.31
0.4
61-80 106
152.8 1.54
1.0
81-100
95
212.7 4.67
101-120
179
301.2 10.25 3.4
2.2
121-140
67
141+
805.5 33.01 4.1
24
489.5 11.27 2.3
The relationship between site and the extent of stem decay in white spruce sampled in the decay survey
of the 1950s was not analyzed because too few trees were sampled to negate the influence of other
factors such as age, cover type, region, etc. However, white spruce damage from root decay (butt decay,
windthrow, etc.) has been reported to be greatest on dry sites and least on wet or moist sites (Whitney
1976). The relationship was similar to that in black spruce, but was not as strong.
Butt decay accounted for 62.3% of the stem-decay volume and 72.9% of the advanced decay present in
the 564 white spruce examined in the provincewide decay survey. Similar results were found in the
Maritime provinces, where 72% of the decay volume was composed of butt decay (Davidson and
Redmond 1957). In Ontario, almost three-quarters of the stem decay was in the advanced stage
(Basham and Morawski 1964). Almost half of the advanced decay was white pocket decay, caused
primarily by Fomes pini (renamed Phellinus pini) in the trunk and Polyporus tomentosus (renamed
Inonotus tomentosus in the butt regions (Fig. 10). Most of the incipient decay was red, and was also
caused by these two fungi. A detailed description of white pocket decay is presented in the section on
white pine. Most of the rest of the stem decay was yellow stringy butt decay, a yellow-orange to yellowbrown decay with pockets in the spring wood that sometimes coalesce and cause separation of the
annual rings. In the more advanced stages of infection, the wood is reduced to a loose, stringy mass of
fibers, and eventually cavities form in the center of the stems. Corticium galactinum (renamed
Scytinostroma galactinum) was the principal cause of this defect (Fig. 10), although several other fungi
caused decays similar in appearance. The principal cause of root decay was Armillaria sp. (probably A.
ostoyae) (Whitney 1978), although it was never isolated from the 564 white spruce in the decay survey
of the 1950s. As in the case of black spruce, this is a reflection of the fact that Armillaria generally stays
within the root system or does not extend very far up into the stem.
Figure 10. White spruce stem decays. (a) radial close up view of advanced decay caused by Fomes pini
(Phellinus pini) showing pockets of cellulose, (b) transverse view of advanced decay caused by Polyporus
tomentosus (Inonotus tomentosus), (c) transverse section of basal stem region with advanced decay
caused by Corticium galactinum (Scytinostroma galactinum).
In a study of the association of stem scars caused by logging with stem decay in white spruce in British
Columbia, it was found that, after 15 years, practically all root and ground-contact scars were infected,
as were 70% of the scars in the butt region and 38% in the upper bole (Parker and Johnson 1960).
However, nearly 100% of scars with an area greater than 0.09 m2 (1 ft2) were infected, regardless of
position. Scars on relatively large-diameter trees were more frequently infected than scars on smallerdiameter trees. As in black spruce, decayed white spruce frequently look exactly the same as sound
trees. The only useful external indicators of decay are stem wounds, broken tops, and fruiting bodies of
P. tomentosus on the lower stems or on the ground nearby in late summer and early fall (for a
description, see the section on red pine).
All stem decays in white spruce, with the exception of relatively rare brown cubical butt decays, are
caused by white-rot fungi, and therefore wood in the incipient stage of decay can be used in chemical
pulping processes, as can small amounts of wood in the advanced stage, provided it is mixed as
uniformly as possible with sound wood. The volume of stem decay in white spruce is seldom extensive
enough to be of concern, regardless of age when harvested. Windthrow and mortality caused by root
and butt decay can be serious in stands over 120 years of age. This danger can be minimized by reducing
the likelihood that basal stems and roots will be injured, particularly by fire or during harvesting
operations, and by minimizing exposure of trees or stands to wind.
Balsam Fir
Of Ontario’s coniferous species, balsam fir is the most susceptible to stem decay. This is evident in Table
6, which shows the percentage of merchantable stem volume decayed or stained, by age class, for the
1,388 balsam fir sampled in the provincewide decay survey. Only very overmature jack pine, older than
140 years, had higher percentages of decay volume. Changes with age in average volumes culled as a
result of decay, as well as changes in total and net merchantable stem volumes for the 1,388 balsam fir,
are shown in Figure 11.
Table 6. Occurrence of decay and stain in the stems of 1,388 balsam fir sampled in Ontario. Based on
trees examined as part of the federal-provincial decay survey of the 1950s. Of the 1,388 trees 1,139
were in the Boreal Forest Region and 249 were in the Great Lakes-St. Lawrence Forest Region.
Age class
No. of Avg. merch.
(years) trees
volume (dm3) stain vol. (dm3) defective (%)
21-40 17
31.9
0.23
0.7
41-60 222
57.3
4.51
7.9
61-80 568
92.7
5.67
6.1
80-100
352
132.3 13.50 10.2
101-120
148
132.5 26.22 19.8
121-140
55
169.9 25.56 15.1
141+
187.5 43.30 23.1
26
Avg. decay and Stem volume
Figure 11. Average total merchantable volume, volume culled as a result of decay, and net volume of
balsam fir in relation to tree age. Volume-age data obtained from curves in Morawski et al.’s (1958)
figure 14, courtesy of the Ontario Ministry of Natural Resources.
Because of the high incidence of decay in balsam fir, a relatively large number of studies of stem decay
in this species had been carried out by 1957 (McCallum [1928] and Pomerleau for Quebec, Kaufert
[1935] for the Lake States, Spaulding and Hansbrough [1944] for New England and New York, Basham [
1950] for Ontario, and Davidson [1957] for the Atlantic provinces). Despite differences in climate, soil
conditions, tree growth rates, etc., the researchers conducting these studies drew remarkably similar
conclusions about the age at which balsam fir should be harvested to avoid serious decay losses,
namely, 70 to 80 years. Their results were based on the progress of decay within individual trees, but in
a study of balsam fir stem decay in the Lake States, a similar pathological rotation age was arrived at on
a stand basis (Gevorkiantz and Olsen 1950). In most of these studies it was mentioned that tree
mortality and windthrow as a result of butt and root decay were not fully taken into account, and that
had this been done, somewhat lower rotation ages would probably have been recommended. Redmond
(1957), studying root rot in young balsam fir stands in New Brunswick, observed that windthrow was
often common in stands by age 75, and therefore recommended the shortest rotation that would
produce trees of merchantable size. The first study of balsam fir decay that included careful
observations of mortality and windthrow caused by root and butt decay was carried out in Upper
Michigan by Prielipp (1957). He recommended three rotation ages, depending on site and soil conditions
(discussed below), with an average rotation age of 55 to 60 years. In the first study in which root decay
was examined and measured in the Boreal Forest of Ontario, Whitney (1989) found that root decay in
stands up to age 90 was more extensive in balsam fir than in spruce, and total losses to windthrow and
butt decay were higher. He recommended a rotation age for balsam fir of less than 65 years when
potential crop-tree mortality, windthrow and stem-decay losses are considered.
Prielipp (1957) found that balsam fir in Upper Michigan grew best but had the most decay and losses to
decay on uplands, whereas it was relatively sound, but grew more slowly, on wet sites. He
recommended earlier rotation ages on upland sites for that reason. Other investigators found that stem
decay in general, and butt decay in particular, were more extensive in balsam fir growing on upland sites
or “mixedwood slopes” than on lowland sites or “softwood flats” (Kaufert 1935; Heimburger and
McCallum 1940; Basham et al. 1953). Brown cubical butt decays, in particular, were rarely found in
balsam fir on softwood flats (Basham et al. 1953). Whitney (1976) reported that root decay in balsam fir
was more extensive on dry or fresh sites than on moist or wet sites in the 31- to 60-year age class, was
most extensive on dry sites in the 61- to 90-year age class, but was of roughly the same intensity on all
sites at ages above 90 years. This very likely reflects the fact that many of the balsam fir trees that
develop the most extensive root decay on dry and fresh sites are eliminated from the stands by the time
they reach 90 years of age.
According to Whitney and MacDonald (1985), there is a relationship between the presence of butt
decay 15 cm above ground level and the growth rate of balsam fir trees in northern Ontario. In 1,612
trees of all ages, these researchers reported that trees with butt decay had average height and diameter
increments over the most recent 3 years that were 13.5 and 10.9% smaller, respectively, than trees with
no butt decay. Spaulding and Hansbrough (1944) and Basham (1950) reported higher percentages of
decay in merchantable stem volume of balsam fir in slower-growing than in faster-growing trees up to
about age 70 in the northeastern United States and in Ontario, after which the situation is reversed.
Both of those studies showed that the extent of stem decay increases with tree diameter, not only in
volume but also as a percentage of the merchantable stem volume. Balsam fir grew much faster in the
northeastern United States than in northern Ontario, with a 70-year-old tree averaging 210 dm3 in the
former region and 93 dm3 in the latter. Therefore, whereas Spaulding and Hansbrough (1944)
recommended harvesting stands before average diameters of over 11 in. (28 cm) were reached in the
northeastern United States because of stem decay, Basham (1950) recommended 7 to 8 in. (18-20.5 cm)
as the diameter limit in Ontario.
Trunk decay accounted for 74.6% of the stem decay encountered in the 1,388 balsam fir sampled in the
provincewide decay survey of the 1950s (Basham and Morawski 1964). In another study in which 933
balsam fir in Ontario were examined, the percentage of trees with butt decay was greater than that of
trees with trunk decay up to age class 61-80 years, after which the reverse was true (Basham 1950). In
Michigan, Prielipp (1957) found that the percentage of the merchantable stem volume of balsam fir
affected by butt decay was greater than that affected by trunk decay until 80 years, after which the
situation was reversed.
The most extensive type of stem decay in balsam fir is a reddish-brown decay frequently called “red
heart rot”. In its incipient stage, it is red to red-orange. Primarily a trunk decay, it is occasionally found in
the butt region. This decay is caused by Stereum sanguinolentum (renamed Haematostereum
sanguinolentum), which belongs to the white-rot group of fungi (Fig. 12a,b,c). On the transverse face of
infected logs, rays often extend outward from the central core of the decay, or the decay can appear as
irregular patches. In an advanced stage of decay, wood becomes dry and friable, and develops a stringy
texture. Trees with advanced “red heart” frequently have decay extending for a considerable length
within the stem. This type of decay accounts for roughly 80% of the defect in balsam fir stems in Ontario
(Basham and Morawski 1964). The remainder is butt decay, most of which is yellow-orange with a
stringy texture and is caused by several fungi that belong to the white-rot group. Corticium galactinum
(renamed Scytinostroma galactinum) is the most common of these (Fig. 12d,e), followed by Odontia
bicolor (renamed Resinicium bicolor), Armillaria sp. (probably A. ostoyae), and Poria subacida. Brown
cubical butt decay is more widespread in balsam fir than in any other conifer in Ontario. In eastern
North America, this decay was found in approximately 10% of 2,800 trees sampled, but on mixedwood
slopes (uplands) the percentage increased to 15.3% (Basham et al. 1953). In the early stages of brown
cubical decay, the wood becomes yellowish to light buff in color, and is slightly softened. As the decay
progresses, the wood becomes dark brown and breaks up into irregular cubical sections. In the
advanced stage, these cubes can be crushed easily to a fine powder. Three fungi - Coniophora puteana
(Fig. 12f), Polyporus balsameus (renamed Tyromyces balsameus), and Merulius himantioides (renamed
Serpula himantioides)-cause brown cubical butt decay in balsam fir, apparently with roughly the same
frequency. These are all members of the brown-rot group of wood-decaying fungi. In examining root
systems and 15-cm stumps of 650 balsam fir in northwestern Ontario, Whitney (1978) isolated, in order
of frequency, A. mellea, C. galactinum, O. bicolor, C. puteana and S. sanguinolentum, as well as several
other fungi.
Figure 12. Balsam fir stem decays. (a) transverse and radial views of “red heart” caused by Stereum
sanguinolentum (Haematostereum sanguinolentum), (b) and (c) transverse sections of “red heart”
caused by S. sanguinolentum, (d) transverse view and (e) radial view of yellow stringy butt decay caused
by Corticium galactinum (Scytinostroma galactinum), (f) transverse radial views of brown cubical butt
decay caused by Coniophora puteana.
For many years it was believed that S. sanguinolentum, the cause of virtually all of the trunk decay in
balsam fir, entered stems via dead branches and branch stubs. In the early 1960s, Davidson showed
that, although most infections entered by way of live branches, the fungus rarely infected dead
branches or branch stubs; the fungus became established in living branches through wounds on those
branches, or through dead and broken branch terminals (Davidson and Newell 1962; Davidson and
Etheridge 1963). Branches more than 2.5 cm in diameter had six times as many infections as branches
less than 1.3 cm in diameter. Stillwell (1956) found that balsam fir leaders more than 1.2 cm in diameter
that were killed as a result of defoliation by spruce budworm were almost invariably entrance points for
S. sanguinolentum decay. This fungus can also gain entry to stem heartwood through forks, frost cracks,
felling scars and broken tops, but large wounded or tip-killed branches are by far the most common
means of entry. The discovery by Whitney (1978) of S. sanguinolentum in about 6% of the balsam fir
root systems he examined does not necessarily mean that the fungus can also infect trees through root
systems. The decay is known to spread vertically in the stem relatively rapidly, and as mentioned earlier,
was sometimes observed extending down to stump level. Its presence in root systems very likely
represents further downward extensions from stem infections.
In tracing the origin of balsam fir butt decays, Spaulding and Hansbrough (1944) determined that 91 %
entered through root systems and the remainder through basal stem wounds such as frost cracks or
mechanical wounds. Because balsam fir is a shallow-rooting tree, lateral roots near the stem are
frequently exposed, predisposing them to wounding and infection by butt-decay fungi. Redmond (1957)
reported that stone bruises in the root systems were major courts of entry for butt decays in balsam fir.
Because balsam fir is a relatively defective, widespread tree of some economic importance, the search
for reliable external indicators of internal decay in living trees has involved balsam fir more than any
other species in northeastern and north-central North America. The largely negative results reflect the
general situation for forest trees, that stem decay is frequently a hidden disease condition. Kaufert
(1935) found stem decay in 59% of the balsam fir he examined in Minnesota, but only 18% had visible
wounds or indications of decay, and a minority of these latter trees had no stem decay. In New England
and New York, Spaulding and Hansbrough (1944) found that 88% of the balsam fir with stem decay had
absolutely no external evidence of that fact. Of the trees with suspicious signs (such as frost cracks,
mechanical wounds or forks), an average of 30% had completely sound stems. These authors reported
that dead branches or branch stubs with much larger than average diameters are likely entrance courts
for decay, but that these were as common in sound as in decayed trees. In more recent studies of
external signs of balsam fir stem decay, Basham (1950) in Ontario, Prielipp (1957) in Michigan, and
Lortie (1968) in Quebec basically agreed that the best indicators are exposed, damaged roots,
mechanical injuries, large branches, frost cracks, forks and woodpecker holes.
Hunt and Whitney (1974) tested yellow stringy butt decay and “red heart” decay (mostly incipient) of
balsam fir for use in the kraft-pulping process. They concluded that both defects had “somewhat lower
kraft pulp yields and pulp strength values than the corresponding sound wood”, but that there would be
no economic losses and the harmful effects would hardly be noticed if defective wood were limited to
10% of total mill chip supply. Such decayed wood should never be used in groundwood pulping, even
when the decay is in the incipient stage, and brown butt decays should never be used in any pulping
process. Although he did not state which pulping process(es) he was referring to, Mook (1966) claimed
that incipient yellow butt decays in balsam fir “do not appreciably reduce wood-fiber strength, and little
bleaching is needed”. He also stated that S. sanguinolentum red heart, unless in the advanced stage, can
be pulped “without appreciable loss in product strength”.
As with other conifers, butt decays in balsam fir that appear extensive at stump height usually extend
less than 1 m up the stem, and can be largely eliminated by bucking short lengths (often as little as 0.5
m) from the base of the stems. Because large-diameter branches are the main source of trunk decay,
relatively high-density young stands that promote early self-pruning will help to minimize this problem.
Any steps that promote tree vigor and rapid growth will also reduce the incidence of stem decay. Where
small balsam fir sawlogs are produced, treatments to induce faster growth are almost essential.
Releasing balsam fir overtopped by hardwoods, and periodic thinnings in which wounded, forked, or
large-branched trees are removed, are also recommended, but injuries to uncut trees should be kept to
a minimum. To avoid extensive stem decay, and mortality or windthrow as a result of root and butt
decay, balsam fir should not be left much beyond 60 years on upland sites, 70 years on “transition” sites,
and 80 years on lowland sites. In pulpwood operations, accessible balsam fir stands are generally
harvested before these ages are reached because many trees attain merchantable size before those
ages and early harvesting reduces the chance that they will be destroyed by the spruce budworm. If
stands must be left beyond those ages, serious losses from root and stem decay and from budwormcaused mortality are almost inevitable.
Larch
To my knowledge, no studies have been carried out in Ontario on stem decay in larch (tamarack). When
the provincewide decay survey was carried out in the 1950s, larch was not included. At that time,
mature trees were rare because of severe decimation of the species by the larch sawfly some 50 years
earlier, and there was some doubt that the species would ever be of commercial importance in the
future. At the present time, the introduction of larch sawfly parasites appears to have reduced the
impact of this pest in Ontario to the point at which the restoration of larch as a useful and commercially
important species can be anticipated.
In a survey of forest-tree diseases in the Lake States, Lorenz and Christensen (1937) concluded that stem
decay in larch was less serious than it was in other conifers. They found some trunk decay caused by
Fomes pini (renamed Phellinus pini), some butt decay (with the brown cubical type apparently more
common than the yellow, stringy type), and root decay caused by Armillaria sp.
Hemlock
For the 387 hemlock sampled in Ontario in the provincewide decay survey, the percentage of
merchantable volume that was affected by stem decay within various age classes is shown in Table 7.
Although hemlock is more defective than many other conifers in the province, particularly in the
younger age classes, the increase with age in the percentage of stem volume decayed is relatively
gradual. There is no dramatic increase as trees pass from maturity to overmaturity as there is in jack
pine, white pine and balsam fir. This fact, coupled with the longevity of hemlock and the relatively rapid,
steady increase in merchantable volume with age even in older trees, makes stem decay of relatively
minor importance in the selection of harvest age.
Table 7. Occurrence of decay and stain in the stems of 387 hemlock sampled in Ontario. Based on trees
examined as part of the federal-provincial decay survey of the 1950s. Trees were in stands throughout
the Great Lakes -St. Lawrence Forest Region, mostly in the Algonquin ecological section.
Age class
No. of Avg. merch.
(Years) trees
vol. (dm3)
stain vol. (dm3) defective (%)
61-80 8
15.0
0.25
5.0
81-100
29
33.0
1.19
5.2
101-120
40
56.1
4.55
8.1
121-140
38
95.1
8.63
9.1
141-160
46
173.6 14.77 8.5
161-180
66
379.0 38.29 10.1
181-200
64
469.2 56.29 12.0
201-220
43
866.4 99.64 11.5
221-240
28
1,085.8 148.77 13.7
241+
2,069.3 384.85 18.6
25
Avg. decay and Stem volume
The sample of 387 trees was too small for meaningful comparisons of the development of stem decay in
hemlock on different sites. The data did suggest that variations in the extent of decay on different sites
were minor and of little practical significance (Morawski et al. 1958). As tree diameter increased there
was a fairly uniform increase in the volume culled as a result of stem decay and in the volume rendered
unusable by the presence of shake (separation of wood along the boundary between annual rings) (Fig.
13).
Figure 13. Average total merchantable volume, volume culled as a result of decay and shake, and net
volume of hemlock in relation to tree diameter. Volume-diameter data obtained from curves in
Morawski et al.’s (1958) figure 38, courtesy of the Ontario Ministry of Natural Resources.
Trunk decay accounted for 81% of the volume of stem decay in the 387 hemlock sampled. Ninety
percent of the trunk decay was advanced “red heart” decay or incipient red decay caused by Stereum
sanguinolentum (renamed Haematostereum sanguinolentum [Fig. 14]). These decays have been
described in the section on balsam fir. The remaining 10% of trunk decay was a yellow stringy decay
caused by several different fungi.
Figure 14. Hemlock stem decay caused by Stereum sanguinolentum (Haematostereum sanguinolentum).
Transverse views of (a) incipient-to-advanced decay, and (b) advanced decay, with a lateral decay pocket
associated with a branch-stub protuberance.
Slightly more than half of the butt decay was made up of S. sanguinolentum “red heart” or extensions of
incipient red decay downwards into the butt region. Most of the remainder was yellow stringy butt
decay, caused by Corticium galactinum (renamed Scytinostroma galactinum) and other members of the
white-rot group of fungi. This type of decay has been described in detail in the section on white spruce.
Brown cubical butt decay was extremely rare. Shake was quite common in the lower trunks of the larger
overmature trees; though not caused by fungi, this condition reduces recoverable volumes.
Little is known about how hemlock stem-decay fungi enter the host trees. It is safe to assume that C.
galactinum and the other butt-decay fungi enter through the root system and perhaps through basal
stem wounds. Stereum sanguinolentum probably uses the same entry points as in balsam fir, namely
wounds or dead tips on living branches (especially large-diameter branches), broken or dead tops, and
other stem wounds. Again, the prevention of stem and branch wounds, excessively large branches, and
dead tops will help to minimize the extent of stem decay in this species.
Eastern White Cedar
A relatively small sample of 116 white cedar trees was processed in the provincewide decay survey of
the 1950s, entirely within the Great Lakes-St. Lawrence Forest Region. The occurrence of stem defect in
the sample, by age class, is shown in Table 8. Only one age class, 41 to 60 years, was adequately
sampled. However, the results do give an indication of how much stem decay can be expected in white
cedar in south-central Ontario.
Table 8. Occurrence of decay and stain in the stems of 116 white cedar sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Merchantable
Age class
No. of merch. Avg. decay and volume
(years) trees
vol. (dm3)
stain vol. (dm3) defective (%)
21-40 11
39.6
0.0
0.0
41-60 45
70.6
0.21
0.3
61-120
16
118.1 5.41
121-140
12
175.6 34.60 19.7
141-160
10
246.4 63.84 25.9
161+
401.6 122.48 30.5
22
4.6
Table 8 shows that, whereas white cedar stems under age 60 years were virtually defect-free, trees aged
between 60 and 120 years had roughly 4.6% of their merchantable stem volumes decayed, and trees
more than 120 years old were quite heavily (>20%) decayed. Most of the decay was in the advanced
stage, and brown cubical decay was the most common type; it accounted for about 70% of the
advanced decay in this species. The remaining advanced decay was either a reddish stringy decay or a
yellow-brown stringy decay. These three types of advanced decay were present in both trunk and butt
regions of the stem. About 10% of the entire defective volume in white cedar was a reddish-brown
incipient decay, present in the butt region but much more common in the trunk region. Several decaycausing fungi were isolated from these decays in white cedar stems, with no single fungus dominant in
frequency of occurrence.
White cedar was encountered mostly on wet-to-moist sites. It was observed that trees on the drier
portions of swamps and on knolls tended to have more decay than trees on wetter sites. Because cedar
is a relatively shallow-rooted tree, windthrow caused by butt and root decay is fairly common. According
to Baxter (1943), woodpecker holes and unusually rough bark are two of the most reliable external
indicators of internal stem decay.
Hardwoods
Trembling Aspen
The presence of stem decay and stain in living trembling aspen is a major reason that this species is
underutilized in Ontario and elsewhere. Stain (discolored but firm wood) accounts for 50 to 65% of the
stem-defect (decay plus stain) volume in aspen 20 to 60 years of age in Ontario, and for 35 to 48% in
aspen more than 60 years old (Basham and Morawski 1964). Unfortunately, gross overestimations of
the extent of stem decay in aspen have been published because authors did not differentiate between
stain and decay, and referred to both as decay (or rot). Nevertheless, the second-last column of Table 9
shows that decay alone is more extensive in aspen, at comparable age classes, than decay plus stain is in
many of Ontario’s major coniferous species (Tables 1 to 8). Table 9 and Figure 15 are based on the 2,458
aspen sampled throughout Ontario in the decay survey of the early 1950s. Figure 15 indicates that,
within individual aspen, the increase in decay and stain volume is so relentless that the average net
(sound) merchantable volume begins to decrease after age 125.
Table 9. Occurrence of decay and stain in the stems of 2,458 trembling aspen sampled in Ontario. Based
on trees examined as part of the federal-provincial decay survey of the 1950s. Of the 2,458 trees, 2,343
were in the Boreal Forest Region and 115 were in the Great Lakes-St. Lawrence Forest Region.
Avg.
Avg. defective
Age class
No. of merch. (decay and stain)
(years) trees
vol. (dm3)
vol. (dm3)
21-40 28
61.7
2.6
4.81
7.8
Merch. vol.
decayed (%)
Merch. vol.
defective (%)
41-60 638
136.4 18.17 6.3
13.3
61-80 666
291.2 50.64 9.2
17.4
81-100
538
516.8 122.50 12.9
23.7
101-120
186
803.3 261.05 21.1
32.5
121-140
350
705.6 262.49 19.9
37.2
141+
907.3 382.86 25.9
52
42.2
Figure 15. Average total merchantable volume culled as a result of decay and net volume of aspen, in
relation to tree age. Volume-age data obtained from curves in Morawski et al.’s (1958) figure 17,
courtesy of the Ontario Ministry of Natural Resources.
About the same time the provincewide decay survey was initiated, the federal forest pathology
laboratory in Ontario received requests from the pulp and paper industry for more information on aspen
stem decay. Consequently, a separate investigation directed specifically at aspen decay was carried out
in the Caramat-Stevens-Manitouwadge region of northern Ontario (Basham 1960). This was on the
timber limits of one of the companies that was pioneering the use of aspen for pulp at that time,
Marathon Paper Mills of Canada Limited. The results of this study are shown in Table 10, which indicates
that somewhat less total defect at ages above 100 years and much less decay at all ages were found in
aspen in this region than in the Boreal Forest Region as a whole (Table 9). The differentiation of stain
and early, very incipient decay is somewhat subjective, and this may account for some of the differences
in the reported extent of decay. However, observations and discussions with others indicate that soil,
climate and other conditions in the the Caramat-Stevens-Manitouwadge region are particularly
favorable for aspen development and growth. It is not surprising, therefore, that the aspen in this region
have a smaller percentage of merchantable stem volume containing defects than the provincial average.
Table 10. Occurrence of decay and stain in the stems of 1,754 trembling aspen sampled in the CaramatStevens-Manitouwadge region of Ontario from 1952 to 1955.
Avg.
Avg. defective
Age class
No. of merch. (decay and stain)
(years) trees
vol. (dm3)
41-60 131
180.1 24.50 1.0
13.6
61-80 271
373.2 64.93 2.7
17.4
81-100
553
461.4 106.59 5.0
23.1
101-120
357
548.1 147.96 8.1
27.0
vol. (dm3)
Merch. vol.
decayed (%)
Merch. vol.
defective (%)
121-140
165
874.1 276.23 8.0
31.6
141-160
238
1,150.9 428.11 14.6
37.2
161-180
39
1,141.1 470.15 16.8
41.2
In the Caramat-Stevens-Manitouwadge region, the percentage of aspen with stem decay increased
steadily with age (Basham 1958b). In the 41- to 60-year age class, 27% of the trees had some stem
decay, and by the 161- to 180-year age class, 100% were decayed, with the biggest increase occurring
between age classes 81-100 (58%) and 101-120 (89%) years. Of perhaps greater significance is the fact
that when only trees with stem decay were considered, the average volume of decay per tree was 8.5
dm3 in age class 41- 60 years in comparison with approximately 200 dm3 in trees more than 140 years
old (Basham 1958b). On a stand basis, when defect deductions were made in accordance with Ontario’s
scaling regulations, the net merchantable volume per hectare reached a peak at age 90 years and the
net merchantable mean annual increment peaked at age 60 (Basham 1960). Undoubtedly, some tree
mortality as a result of windfall and suppression is reflected in these results.
For Ontario as a whole, a rotation age of not more than 80 years has been recommended for trembling
aspen to avoid extensive losses to stem decay and stain (Basham and Morawski 1964). For pulpwood, an
even shorter rotation of 60 years has been suggested (Morawski et al. 1958). In the Lake States,
pathological rotation ages (i.e., the ages at which trees should be harvested to minimize the volume lost
to decay) of 55 to 60 years (Strothmann and Zasada 1957) and 50 years (Anderson et al. 1978) have
been recommended for aspen.
Before the relationships between stem decay in aspen and factors other than age are considered, the
clonal growth habit of this species warrants attention. The majority of aspen stands in Ontario originate
from suckers that develop from tree root systems. Many, perhaps most, of those stands are composed
primarily of groups (clones) of genetically identical trees. Each clone originated, perhaps centuries ago,
from a single tree of seedling origin. Hence, whereas each tree is an individual and unique genotype for
most other tree species, all the trees in a single group may be of identical genotype for trembling aspen.
Pronounced interclonal variability has been documented for several traits, including growth rate, stem
form, phenology and wood properties (Kemperman 1977). In Manitoba, Wall (1971) found highly
significant differences among aspen clones in the percentage of stem decay, and in decay volume, gross
tree volume and net tree volume. In northern Ontario 60 clones in six different aspen stands (10 clones
in each stand) were studied, and several clones with relatively fast growth rates and superior stem form
were easily identified. However, the majority of these superior clones had excessive stem decay, and
only two of the 60 clones could be classed superior as far as growth rate, stem form, and stem
soundness (relatively little decay) were concerned. In Manitoba, Wall (1971) also found that relatively
fast tree growth combined with relatively little stem decay was seldom found in a single clone.
It is clear that, in aspen stands composed largely of clones, the clone rather than the individual tree
should be the basic sampling unit. The fact that this was not done in most studies before 1970 casts
doubt on the validity of results concerning relationships between the extent of stem decay in aspen and
factors such as site, tree growth rate, and diameter. It is not surprising that most attempts to relate the
extent of aspen stem decay to site in such studies yielded inconclusive results. Using height growth of
trees to classify sites, Riley (1952) and Morawski et al. (1958) found no relationship between site and
stem decay in Ontario. When soil moisture regime was used to differentiate sites, the drier sites tended
to have the most stem decay, but this relationship was not particularly strong (Strothmann and Zasada
1957; Basham 1958b; Morawski et al. 1958). In the provincewide decay survey of the 1950s, the
majority of the 2,343 aspen sampled in the Boreal Forest Region were on fresh sites (moisture regimes 2
or 3), whereas almost all of the 115 aspen sampled in the Great Lakes-St. Lawrence Forest Region were
on dry sites (moisture regimes 0 or 1). Most trees in the latter region were in the 41- to 60-year or 61- to
80-year age classes. The average percentage of merchantable stem volume affected by decay or stain
was greater for aspen in both of these age classes in the Great Lakes-St. Lawrence Forest Region than in
the Boreal Forest Region. This suggests that aspen on sites with moisture regimes of 0 or 1 are more
defective than aspen on sites with moisture regimes of 2 or 3, although other factors such as climate,
soil depth, soil nutrients and, of course, clonal differences may have been partly or wholly responsible
for the observed difference in average extent of stem decay. In one study of a single aspen clone that
had grown to cover three adjacent but distinctly different sites (on the basis of soil moisture regimes),
analysis of variance revealed that the only significant difference was in tree height; differences in the
extent of decay were not significant (Weingartner and Basham 1985). In Manitoba, Wall (1971) found
that, where aspen from the same clone grew on different sites, differences in the percentage of stem
volume decayed were not significant. Consequently, it appears that if site has any influence on the
extent of stem decay in trembling aspen, it is of minor importance in comparison with clonal (genetic)
influences.
In the aspen-decay study carried out in the 1950s in the Caramat -Stevens -Manitouwadge region of
Ontario, the 1,754 trees sampled were divided into two groups, those <24 cm DBH and those ³24 cm
DBH (Basham 1960). Figure 16 shows that a greater percentage of the gross merchantable volume of the
smaller trees than of the larger trees within even-aged stands was culled because of stem decay
(Ontario scaling regulations). The difference increased with increasing stand age, and was particularly
pronounced in stands more than 90 years old. Clones were not considered in that study, but this result
fostered the hope (later dashed) that faster-growing clones would be more decay resistant than slowergrowing clones. From more recent studies of aspen clones and stem decays, we can now postulate that,
within clones, the trees with lower diameter-growth rates have higher percentages of stem decay than
do faster-growing trees, because the occurrence and rate of spread of stem decay is not dependent
upon tree growth rate and is roughly the same in slow- and fast-growing trees.
Figure 16. Average percentage of merchantable volume culled as a result of decay, in relation to stand
age, in aspen trees <24 cm DBH and ³24 cm DBH. Volume-diameter data obtained from curves in
Basham’s (1960) figure 31.
All of the foregoing studies of aspen decay in Ontario were carried out on the Canadian Shield. Replies
to a questionnaire were received from 39 hardwood industries that process poplar south of the
Canadian Shield; these indicated that stem decay and stain in southern Ontario are not serious problems
(Basham 1973a).
In the 2,458 aspen sampled across Ontario in the federal-provincial decay survey of the early 1950s, an
overall average of 15.2% of the merchantable stem volume was decayed and 11.9% was stained
(Basham and Morawski 1964). In the Caramat-Stevens-Manitouwadge study, which involved 1,754
aspen, these figures were 8.7% for decay and 19.9% for stain (Basham 1958b). When decay and stain are
combined, the two studies yield quite similar results, 27.1% of the merchantable stem volume in the
former study and 28.6% in the latter. Butt decay accounted for 12.5% of all stem decay, and 20.3% of
the stain was in the butt region.
In both Ontario studies of aspen decay and stain, three broad types of decay and two distinctly different
stains were observed. About 85% of the stain ranged from light brown to dark, grayish brown. A band of
this stain usually surrounded decay columns; this band was relatively wide when associated with small
or incipient decays but much narrower when it bordered extensive, advanced decays. Brown stain was
usually extensive at stump height. The remaining 15% of stain volume was predominantly red, though
usually mottled in appearance, with yellow, brown, and green hues as well. Occasionally, this mottled
stain replaced brown stain around decay columns, and in many relatively old defective trees it was the
only defect present in the smaller top logs cut in the crown region. Mottled stain was also frequently
associated with knots and branch stubs in trees of all ages. Bacteria, yeasts, and non-decay fungi were
frequently isolated from both stains, although Sucoff et al. (1967) have presented evidence that the
initial development of these stains involves physiological and biochemical processes that take place
without the presence of microorganisms. Similarly, the so-called “wetwood” commonly seen in freshly
cut aspen logs is of non-microbial origin, but once formed, it supports a large bacterial population
(Knutson 1973). Wetwood does not develop into decay, and in many cases it virtually disappears with
time on exposed log faces.
The most common and most serious form of advanced stem decay in aspen in Ontario is a white spongy
decay caused by Fomes igniarius var. populinus (renamed Phellinus tremulae [Fig. 17a,b,c]). This decay is
sometimes called “white trunk rot”, and accounts for approximately 75% of advanced stem decay in
aspen. It occurs primarily as a trunk defect, but is also found in the butt region. Fomes igniarius belongs
to the white-rot group of fungi. Columns of this decay are usually quite extensive, possibly because
some originate from multiple infections. The average volume of white spongy decay in infected trees in
Ontario has been estimated at 96 dm3 (3.4 ft3) (Basham 1958b). In the incipient stage, the wood is
yellowish-white and slightly softened, often separated from the surrounding stained or sound wood by
dark zone lines. The wood quickly becomes very soft, punky, or spongy, and more yellowish, often with
irregular black zone lines in the decayed portion. Most of the remaining advanced stem decay in aspen is
a yellow or yellow-brown stringy decay that occurs in both the butt and the trunk regions. In the trunk it
is caused by Radulum casearium (Fig. 17a,d), which also causes some of the butt decay. Other yellowbrown stringy butt decays are caused by Pholiota spectabilis (renamed Gymnopilus spectabilis [Fig. 17e])
and Armillaria sp. (probably A. ostoyae [Fig. 17f]).
Figure 17. Trembling aspen stem defects. (a) transverse sections showing lightly stained wood (upper
left), incipient decay (upper right), advanced decay caused by Radulum casearium (lower left) and by
Fomes igniarius (Phellinus tremulae) (lower right), (b) conks of F. igniarius below stem breakage caused
by advanced decay. (c) transverse view of decay caused by F. igniarius, (d) transverse and two radial
views of decay caused by R. casearium, (e) bisected stem section, showing advanced stringy decay
caused by Pholiota spectabilis (Gymnopilus spectabilis), (f) advanced stringy butt decay caused by
Armillaria. sp.
The above mentioned relative frequencies of decay-causing fungi in aspen are based on studies carried
out in Ontario in the 1950s, when stems were not examined below 30 cm above ground level, the
average stump height at that time. More recent studies have revealed that Armillaria sp. is of far more
relative importance in aspen than was indicated by its detection in those earlier studies. Decay caused
by Armillaria has been found in the roots and root collars of dominant and codominant aspen suckers at
ages 13 (Basham 1988) and 14 (Basham 1982a) years. Weingartner and Basham (1985) found
considerable butt decay in mature aspen when trees were examined down to ground level. Although the
extent of stem decay caused by Armillaria in merchantable stems of aspen is limited, its principal
impacts are undoubtedly on tree growth rate and on the vulnerability of trees to windthrow.
Trunk decay in aspen caused by F. igniarius can begin as early as age 30 to 35 years, but yellow stringy
trunk decay caused by R. casearium seldom occurs in aspen less than 70 years old. A third Basidiomycete
fungus frequently isolated from defective wood in aspen trunks is Corticium polygonium (renamed
Peniophora polygonia). This fungus is widespread in trees less than 60 years old, then gradually
decreases in abundance until it is virtually nonexistent in trees more than 120 years old. It was
frequently isolated from brown stain in very young trees, and from incipient yellow or yellow-brown
decay. It appears incapable of causing advanced decay, as it was rarely isolated from such wood.
Slightly more than half of the stem decay in aspen in Ontario was classified as incipient decay (Basham
and Morawski 1964). Brown or brown cubical decays, caused by fungi that belong to the brown-rot
group, are extremely rare in this species.
In Ontario, 56 out of 1,754 aspen examined for stem decay had visible basal scars; yellow stringy butt
decay was found in all 56 of them (Basham 1960). Some butt decays, particularly those caused by F.
igniarius and R. casearium, which are normally trunk-decay fungi, enter through such scars, which
appear to be caused primarily by fire, falling trees, or frost. The majority of butt decays, including most,
if not all, of those caused by Armillaria and P. spectabilis, enter through root wounds and
interconnected roots. Since most aspen originate as root suckers, one possible route is from the
decayed stump or roots of the parent tree, through the sucker-producing root into the root system and
basal stem region of the sucker. Branch stubs are evidently the main avenue of entrance to the stem for
C. polygonium (Etheridge 1961). Little is known about the means of entry of R. casearium.
Since aspen is a relatively decadent tree species, and the major cause of decay is F. igniarius, there are
many references in the literature to the means by which this fungus gains entry to aspen stems. In
Ontario, 75 of 1,754 aspen had pronounced trunk wounds or abnormalities, mostly mechanical injuries,
frost cracks, or forked crowns; stem decay was associated with 63 (85%) of these, and many of the
decays were the white spongy type caused by F. igniarius (Basham 1960). However, 90% of the trunk
decays could be traced only to branch stubs, and the majority were F. igniarius spongy decays.
Researchers disagree about whether the primary avenue of stem entrance for F. igniarius is branch
stubs or stem wounds. In one clonal study (Weingartner and Basham 1985), 160 trees in an aspen stand
approximately 40 years old in the Fort Frances region were examined. Small zones of decay
characteristic of F. igniarius were present in 21 of the trees. We carefully dissected each of these
recently developed decay zones, and without exception they appeared to have originated at branch
stubs. More published reports support the idea that branch stubs are the principal point of entry for F.
igniarius than support the view that trunk wounds are the main source. It is probably safe to conclude
that F. igniarius can gain entry to aspen stem wood through both branch stubs and relatively severe
stem wounds. Because branch stubs are so much more common than severe stem wounds on aspen
stems, the majority of F. igniarius infections probably enter through branch stubs.
Trembling aspen differs from most forest tree species of Ontario in that it does have a fairly reliable,
external and easily visible indicator of the extent of internal stem decay. About three-quarters of the
advanced decay in aspen is the white spongy type caused by F. igniarius. In the 1930s Riley and Bier
(1936) reported that conks (sporophores or fruiting bodies) of F. igniarius (Fig. l7b) on 11 aspen in the
60- to 70-year age class at Petawawa, Ontario, were invariably associated with advanced stem decay.
The decay extended a mean distance of 30 to 180 cm above and below the highest and lowest conks.
More recent studies not only confirmed this, but revealed that most of the aspen trees with moderateto-large amounts of advanced F. igniarius decay had one or more conspicuous sporophores of the
fungus growing from their stems. The sporophores are typically hoof- or shelf-shaped, with dark-brown
to black ridged upper surfaces and tan to light-brown undersurfaces that contain small holes or pores
visible to the naked eye.
Sporophores are usually formed at branch knots. In our study in the Caramat-Stevens-Manitouwadge
region of northern Ontario we found that a series of F. igniarius sporophores on a single tree, or
sporophores more than 10 cm wide, were invariably associated with extensive spongy decay (Basham
1958b). In the age classes between 60 and 180 years, from 79 to 97.6% of the aspen infected with F.
igniarius stem decay bore one or more sporophores. Anderson and Schipper (1978) examined this
relationship for aspen in Michigan, Wisconsin and Minnesota. They devised a nondestructive method for
predicting the extent of F. igniarius stem decay in a stand that was based on the basal area of the trees
that bore sporophores.
It should be borne in mind that the absence of F. igniarius sporophores in aspen does not necessarily
mean that the trees have no stem decay. About 20% of trunk decay in aspen more than 70 years old is
caused by R. casearium, which does not produce sporophores on the stems of living trees, and
consequently this decay can be quite extensive in healthy-looking stems. Forked crowns or butts,
mechanical injuries that produced stem scars, fire scars, frost cracks, and unsound knots are frequently
associated with stem decay in aspen. The small, white, flat fruiting bodies of C. polygonium on or near
branch stubs are a sign that extensive stain or incipient decay is likely present in the stem above and
below the stub. Any basal wound, unless very recently inflicted, is almost certainly associated with
yellow stringy butt decay. The presence of Armillaria sporophores at the base of aspen stems or on the
ground nearby is a sign that the root system and perhaps the basal stem is decayed. These sporophores,
or mushrooms, usually appear in clusters and have yellow to golden caps with brownish scales on top
and white gills on the undersurface, and are supported by yellow to brown stalks that can be up to 20
cm tall.
Although trembling aspen is used in many manufacturing processes, including those used to produce
veneer and sawlogs, it is employed mainly by the pulp and paper industry. Because its fibers are not as
long as those of spruce and balsam fir, it lacks the strength of coniferous kraft pulp and is therefore
usually combined with it, often at roughly 10% of the mix. In kraft-pulping tests carried out on sound
and defective aspen wood from Ontario, the yield of oven-dry pulp from decayed (incipient and
advanced) wood was 9.7% less on average than that from sound wood (Hunt et al. 1978). When only
advanced decay was tested, the decrease in yield was 11.5%. The strength of pulp obtained from wood
with incipient decay differed little from that of pulp obtained from sound wood. Advanced decay was
responsible for substantial decreases in pulp strength, with tear factors 20 to 29% lower than for sound
wood. Jackson et al. (1985) have shown that aspen can produce high-yield chemithermomechanical
pulps displaying properties comparable with those of mechanical softwood and chemical hardwood
pulps. However, they pointed out that decayed aspen wood produces pulp of inferior strength and poor
brightness, deficiencies that cannot be compensated for by subsequent bleaching.
Harvesting aspen stands before they reach an age at which excessive stem decay has developed is
essential if serious losses to decay are to be avoided. That age will largely depend on the product
involved. For pulpwood in Ontario, 60 years is recommended. For sawlogs and veneer, where tree size is
important, it is probably safe to allow stands to grow to 80 years except on drier sites, where decay may
develop earlier in some clones. For waferboard production, in which some decayed wood can be used
with little or no deleterious effect on the end product, a rotation age of 90 or even 100 years is feasible.
The extent of stem decay in aspen stands can be reduced by maintaining fully stocked stands in which
the crowns of adjacent trees touch. This promotes early natural pruning, which generally reduces the
number and size of branch stubs, the main avenue of entrance to the stem for F. igniarius decay. Stem
wounding by fire, logging, etc., should be prevented as much as possible. Although clonal management
of aspen stands in Ontario has been proposed (Heeney et al. 1975), the difficulties involved in
identifying relatively decay-resistant clones and the apparent scarcity of clones that combine this with
other desirable characteristics appear to render clonal management unfeasible at present for reducing
the incidence of stem decay in aspen. As far as post-harvest treatments are concerned, Perala (1971) in
the Lake States and Basham (1982b) in Ontario have shown that herbicide spray treatments in young
aspen stands may kill most leaders and some branches, but few trees are killed and the survivors will
apparently produce crop trees with little or no reduction in quality. However, recent studies indicate
that considerable stem and root decay is associated with scarification wounds of 3-year-old aspen
suckers (Basham 1988). Suckers 2 years old or less sustain relatively little damage, and hence decay,
from scarification treatments (Basham, data not yet published). For these reasons, the scarification of
aspen suckers 3 years old or more is not recommended.
Other Poplars
Because largetooth aspen, balsam poplar, and eastern cottonwood are relatively uncommon in Ontario,
insufficient trees have been examined to determine stem-decay patterns and relationships. In the Lake
States, stem decay in balsam poplar caused by Fomes igniarius (renamed Phellinus tremulae) and by
Armillaria mellea (now believed to be mostly A. ostoyae) has been reported (Lorenz and Christensen
1937). In Alberta, Thomas et al. (1960) studied stem decay in balsam poplar and trembling aspen. They
found balsam poplar to be subject to a moderate amount of stem decay, but considerably less than
trembling aspen. More than twice as much decay, on a volume-percent basis, was encountered in aspen
than in balsam poplar. Pholiota spectabilis (renamed Gymnopilus spectabilis) was the fungus most
frequently associated with butt decay in balsam poplar, followed by A. mellea. Fomes igniarius was the
most common cause of trunk decay.
White Birch
White birch has one of the lowest incidences of stem decay among the deciduous species of Ontario.
The second-to-last column of Table 11 shows that the percentage of the merchantable stem volume
decayed in Ontario in trees less than 100 years old averages less than 5%. However, Table 11 also shows
that stain is quite widespread in white birch stems. Indeed, 70% of the volume of defect in the 936 trees
sampled in the provincewide decay survey was a reddish-brown stain. This is commonly known as “red
heart”, and most white birch in a study of 293 trees in Massachussetts had this stem defect by age 50
(Campbell and Davidson 1941 a). Table 11 shows a steady increase, with age, in the extent of defect in
white birch stems up to age class 121-140 years, then a decrease as trees get older. However, the small
sample of 13 trees more than 140 years old casts doubt on the reliability of that result. When white
birch grows where red heart is not a problem, the influence of decay on harvest age or rotation will be
of little consequence (Table 11). However, red heart develops fairly early and can be a problem in trees
used for products that require clear wood. Campbell and Davidson (1941a) report that red heart has
little effect on wood strength or hardness, but tends to check and crack more than clear wood during
drying. They report considerable red heart in white birch more than 70 years old.
Table 11. Occurrence of decay and stain in the stems of 936 white birch sampled in the Boreal Forest
Region of Ontario. Based on trees examined as part of the federal-provincial decay survey of the 1950s.
Avg.
Avg. defective
Age class
No. of merch. (decay and stain)
(years) trees
vol. (dm3)
vol. (dm3)
21-40 2
35.3
0.00
-
-
41-60 77
43.7
1.70
0.9
3.9
61-80 304
81.1
4.86
1.2
6.0
81-100
284
148.9 16.84 2.3
11.3
101-120
165
296.4 61.04 6.7
20.6
121-140
91
253.7 52.28 8.2
20.6
Merch. vol.
decayed (%)
Merch. vol.
defective (%)
141+
13
541.7 95.87 7.7
17.7
The 936 white birch sampled throughout the Boreal Forest Region in the federal-provincial decay survey
of the 1950s grew mostly in mixedwood stands. All but 6% of them grew on either fresh (59%) or dry
(35%) sites (classified on the basis of soil moisture regime). Up to age 80 years, there was little
difference in the extent of stem decay in trees growing on the two sites. However, after 90 years there
was appreciably more decay in trees on the fresh sites; this was partly compensated for by the fact that
tree growth was somewhat faster there than on the dry sites.
Replies to a questionnaire were received from 26 hardwood industries that process white birch in
Ontario south of the Canadian Shield; these indicated that stem decay and stain were not serious
problems in this region (Basham 1973a).
As already mentioned, stain or “red heart” accounted for about 70% of the stem defect in white birch.
The remainder was decay, with advanced decay slightly more common than incipient decay. Butt
defects accounted for 20% of all defective wood; as far as stain was concerned, 17.2% occurred in the
butt region. Red heart has a water-soaked appearance when freshly cut, and is clearly different from
true heartwood discoloration in that it has a higher moisture content than the surrounding sapwood.
Although it usually occurs by itself, in columns that surround the stem pith, when decay was present it
was generally surrounded by a narrow collar of red heart radially, and by extensive red heart vertically.
Siegle (1967) has shown that red heart in white birch is generally triggered by the enzymes of non-decay
fungi, which usually enter the stem through mechanical injuries or frost cracks. This was confirmed by
studies in which very few decay fungi were isolated from red heart (Basham and Morawski 1964).
The most common type of advanced decay in white birch stems was white spongy decay caused by
Fomes igniarius (renamed Phellinus igniarius) (Basham and Morawski 1964). The appearance of this
decay has been described in the section on trembling aspen. Though primarily a trunk decay in most
tree species, including aspen, almost one-third of this defect was in the butt region in white birch. The
remaining advanced decay was a yellow-brown stringy decay; slightly more than one-third of this defect
occurred in the butt region. It was caused mainly by two fungi, Stereum murraii (renamed Cystostereum
murraii), which was more common in the trunk than in the butt, and Pholiota aurivella (often incorrectly
identified as P. adiposa before 1965), which was more common in the butt than in the trunk. Most of
the incipient decay was yellowish and appeared to be caused by several different fungi, including S.
murraii.
It is likely that F. igniarius enters white birch stems through branch stubs and, to a lesser extent, stem
wounds, as in aspen. Stem wounds are probably entry points for the other decay fungi, and are
implicated in the development and spread of red heart stain (Siegle 1967). Most butt infections
originate in basal wounds and root systems. Fomes igniarius produces sporophores on the stems of
living white birch, but far less frequently than on aspen; consequently, there are few external indications
of internal defect in birch. Visible stem wounds certainly indicate that stem decay or at least red heart is
present. However, trees with no visible wounds may also contain considerable defect. To minimize the
impact of red heart, Cooley (1962) recommended partial cutting, with the least vigorous, slowest-
growing trees removed first, and the removal of trees in the upper crown canopy that show signs of top
death. Pruning (either natural or artificial) young trees when branches are small, and growing white
birch only on appropriate sites, are also recommended (Marquis et al. 1969).
Yellow Birch
The sample of 1,418 yellow birch trees in Ontario dissected to measure the extent of stem decay and
stain during the federal-provincial decay survey of the 1950s indicated that this is one of the most
defective tree species in Ontario’s forests (Table 12). Comparison of Tables 12 and 13 shows that yellow
birch is generally more defective than sugar maple, with which it is frequently associated. It would
appear, from Table 12, that approximately one-third of the merchantable stem volume of yellow birch
between ages 100 and 160 years can be expected to be defective, and above age 160 years, about half
may well be defective. Much of this defect is in the form of stain (70%); nevertheless, the average extent
of decay alone is sufficient to rank yellow birch among the most decadent species in Ontario. Again, if
serious economic consequences of stem defectiveness are to be avoided, the maximum harvest or
rotation age will depend on how yellow birch is used. To prevent significant amounts of decay, trees
should be harvested before age 140 years, but if stain is an important consideration, yellow birch should
be harvested before age 101 to 110 years. Because of the relatively high value of yellow birch logs, trees
at those ages may in many instances be considered too small to harvest for veneer and sawlog
operations. Postponing the harvest until the trees are larger will result in higher percentages of decay
and stain, but this may well be compensated for by the increased value of the trees and their products.
Table 12. Occurrence of decay and stain in the stems of 1,418 yellow birch sampled in the Boreal Forest
Region of Ontario. Based on trees examined as part of the federal-provincial decay survey of the 1950s.
Avg.
Avg. defective
Merch. vol.
Age class
No. of merch. (decay and stain)
(years) trees
vol. (dm3)
vol. (dm3)
21-60 108
68.7
0.2
61-80 119
134.2 19.44 1.6
81-100
166
309.4 68.08 4.3
22.0
101-120
143
463.7 139.13 4.6
30.0
121-140
182
689.1 257.03 10.0
37.3
141-160
125
897.7 327.64 9.1
36.5
161-180
139
1,087.4 505.65 17.1
46.5
181-200
97
1,403.9 602.25 12.0
42.9
2.68
Merch. vol.
decayed (%)
3.9
14.5
(%)
defective
201-220
113
1,591.0 747.78 12.8
47.0
221-240
66
1,874.2 864.00 12.3
46.1
241-260
89
2,171.8 1,170.58
16.5
261+
2,588.1 1,426.07
71
21.8
53.9
55.1
The 1,418 yellow birch were sampled in what Halliday (1937) classified as the Algoma and Algonquin
forest ecological sections of Ontario. The 241 trees sampled in the Algoma section grew much more
slowly than those in the Algonquin section; trees of the same diameter were as much as 30 to 40 years
older in Algoma (Morawski et al. 1958). At comparable ages, yellow birch in the Algoma section were
more defective than those in the Algonquin section. For example, trees sampled in the Algoma section
at age 150 years averaged 34 cm (13.4 in.) DBH and 44% of their merchantable stem volume was
defective, in comparison with 40 cm (15.7 in) DBH and 35% of stem volume defective in the Algonquin
section.
Replies to a questionnaire were received from 27 hardwood industries that process yellow birch south
of the Canadian Shield; these indicated that stem decay and stain in this region of Ontario were not
serious problems (Basham 1973a).
The influence of site (soil moisture regime) on the extent of stem decay and stain in yellow birch was
examined in both the Algoma and the Algonquin ecological sections. Trees were separated on the basis
of dry, fresh, and moist moisture regimes. In neither section was there any clear correlation between
site and stem defect (Morawski et al. 1958).
When the 241 yellow birch in the Algoma section and the 1,177 trees in the Algonquin section were
analyzed separately, there was a strong correlation between tree age and diameter. Consequently, it is
not surprising that there was a good positive correlation for each section between tree diameter and
the extent of stem defect (Morawski et al. 1958).
In the 1,418 yellow birch examined for stem defect in the Great Lakes-St. Lawrence Forest Region, 70%
of the defect was stain and the remainder was decay. About 71% of the decay was in the advanced
stage, and just over 23% of the decay was in the butt region of the stem. About 25% of the stain was in
the butt region.
The stained wood in yellow birch was brown or reddish-brown. Almost all trees more than 60 years old
had some stain at a height of 30 cm, the stump height used in the survey. In trees more than 100 years
old the cross-sectional stained area at stump height was frequently quite extensive. In trees with decay
columns, the columns were almost invariably surrounded by narrow stain zones. Much of the stain in
yellow birch is believed to be of physiological-biochemical origin, and to require no microorganisms for
its initiation and development. However, the frequency with which the decay fungus Stereum murraii
(renamed Cystostereum murraii) was isolated from the stained wood (Basham and Morawski 1964)
suggests that an appreciable proportion of yellow birch stain represents early incipient stages of S.
murraii decay.
The most common form of decay in the 1,418 yellow birch trees was a yellow-brown stringy type that
accounted for 71 % of the advanced decay. It occurred in both trunk and butt regions. In the trunk
region, S. murraii (Fig. 18) was the principal cause, distantly followed by Pholiota aurivella (often
incorrectly identified as P. adiposa before 1965). In the butt region, P. aurivella was the decay fungus
most frequently isolated from yellow-brown stringy decay, closely followed by Armillaria sp. (probably
A. ostoyae) and Flammula alnicola (renamed Pholiota alnicola). Practically all of the remainder of the
advanced decay in yellow birch was of the white spongy type, already described in the section on
trembling aspen. This was caused primarily by two very closely related fungi, Fomes igniarius (renamed
Phellinus igniarus (Fig. 181), and Fomes igniarius var. laevigatus (renamed Phellinus laevigatus); a small
amount of this decay was caused by Fomes fonentarius. Fomes igniarius occurred in both butt and trunk
regions, F. igniarius var. laevigatus occurred primarily in the trunk region, and F. fomentarius was limited
to the trunk region. A very small amount of brown cubical butt rot was found; of the four identifiable
isolations made from this defect, three were Coniophora puteana and the other was Poria cocos
(renamed Wolfiporia extensa). The latter fungus was the most common cause of butt decay in a study of
yellow birch stem decay in Nova Scotia (Stillwell 1955). Almost all of the incipient decay in the 1,418
yellow birch examined in Ontario was yellowish. The only decay fungus consistently associated with
incipient decay was S. murraii.
Figure 18. Yellow birch stem decays, (a) transverse view of advanced decay caused by Stereum murraii
(Cystostereum murraii), associated with a severe stem wound, (b) transverse view of advanced decay
caused by Fomes igniarius (Phellinus igniarius).
Several studies conducted outside of Ontario have shed some light on the means by which decay fungi
enter the stems of yellow birch. Shigo (1966) examined defective stem wood associated with logging
wounds in 116 yellow birch in New Hampshire. He found the most common decay fungus in these
associations to be “Pholiota squarrosa-adiposa”; there can be little doubt that this was the fungus
mycologists now call Pholiota aurivella. Davidson and Lortie (1970) examined defective stem wood
associated with stem wounds in eight yellow birch trees in Quebec. They found P. aurivella to be the
only decay fungus consistently associated with decay and stain. From these results it appears likely that
most P. aurivella infections in yellow birch originate from stem wounds. The two other major causes of
stem decay in yellow birch, S. murraii and F. igniarius, were not found in yellow birch by Davidson and
Lortie (1970) and were isolated only once each by Shigo (1966) from 116 wounded yellow birch. These
results support the generally held view that, whereas S. murraii and F. igniarius can invade stems
through stem wounds if conditions are suitable, their usual mode of entry is through dead branch stubs.
In Nova Scotia, Stillwell (1954) found considerable decay caused by F. fomentarius in large yellow birch
branches killed by the “birch dieback” syndrome. The fact that F. fomentarius decay was found only in
the trunk region and never in the butt region of the stems of yellow birch in Ontario suggests that many
stem infections by this fungus originate in large dead branches.
Probably because of the relatively high value of yellow birch and its high incidence of stem decay and
stain, several studies on the relationships between the extent of stem defect and external signs of
defect in living trees have been carried out. The decay-causing fungi seldom produce easily visible
sporophores (fruiting bodies) on living yellow birch trees. Stereum murraii sporophores are small, flat,
and difficult to detect, particularly when they occur high up in the trunk, which is their usual location.
Furthermore, they are not common on living trees. Sporophores of P. aurivella occasionally appear on
living yellow birch, but they are fleshy, annual organs that are present for a relatively brief period in late
summer or fall. The tough, perennial sporophores of the F. igniarius group seldom occur on living yellow
birch, and when they do they are generally flattened against the trunk, unlike the more visible shelf-like
sporophores on trembling aspen.
In various parts of the northeastern and north-central United States, yellow birch stem cankers have
been frequently associated with stem decay. The cankers are generally described as sunken areas with
the bark firmly attached, often impregnated with dark, hardened fungal material, and with slightly
swollen borders. They are reported to be associated with decay caused by S. murraii (Davidson et al.
1941), F. igniarius (Ohman and Kessler 1964), and F. igniarius var. laevigatus (Campbell and Davidson
1941b). Yellow birch cankers of this nature appear to be far less common or noticeable in Canada; they
were not observed as a major indicator of stem decay in the Ontario decay survey of the 1950s, nor are
they mentioned in other Canadian studies of external indicators of stem decay in yellow birch.
Logging wounds inflicted on yellow birch stems are frequently associated with internal stem decay, but
“decay and discoloration following logging wounds... definitely cannot be explained or predicted on the
basis of external characters or features alone” (Shigo 1966). Appreciable decay was associated with
large basal logging scars 4 years after they were inflicted (Benzie et al. 1963). Felling scars or other
mechanical injuries that involve death of the cambium would likely have similar effects. Lavallée and
Lortie (1968), in a study of external features and stem decay in living yellow birch in Quebec, concluded
that mechanical injuries are more reliable indicators of stem decay than are the more frequently
occurring branch stubs and broken branches. They found that, in general, the larger the wound surface
area, the more decay, and that besides mechanical injuries, frost cracks and large holes were also
frequently associated with stem decay. Poorly healed branch stubs more than 6.3 cm (2.5 in.) in
diameter or dead branches in that size class were usually associated with some stem decay; however,
stubs or dead branches 3.8 cm (1.5 in.) in diameter or less were seldom associated with stem decay
(Lavallée and Lortie 1968).
Shigo (1965a) and Lavallée and Lortie (1968) suggested that the abundance, size and distribution of
branch stubs on individual trees is the most reliable external indication of the amount of stain in the
central core of yellow birch stems. Extensive stain columns were frequently associated with several
branch stubs that were fairly close together Lavallée and Lortie 1968), or with relatively large-diameter
branches that died late in the life of the tree (Shigo 1965a). In both of these studies it was observed that
trees with little stem stain were generally those that self-pruned their branches at a relatively early age,
when the branches were small. Hence, any practice that results in young stands in which yellow birch
are sufficiently close to their neighbors that self-pruning takes place should minimize the occurrence of
stain in the stems of mature, crop-size trees.
Because stain frequently becomes extensive in yellow birch as early as age 101 to 110 years in Ontario,
and decay becomes extensive at age 140 years under average conditions, yellow birch should be
managed to avoid serious stain and decay problems and to promote vigorous, fast-growing trees that
will attain merchantable size before they reach these ages. Clearly, doing as much as possible to prevent
stem wounding of potential crop trees, particularly during logging operations, will also help to minimize
the impact of stem decay on yellow birch. On the basis of defect indicators in second-growth yellow
birch (as well as sugar maple and beech) in Quebec that had resulted largely from past clearcuts or
partial cuts, Winget (1969) recommended clearcutting tolerant hardwood stands to improve the quality
of potential crop trees. Skilling (1959) studied the effects of pruning 20-year-old yellow birch on tree
growth rate and quality. He found that pruning had no adverse effects on tree growth rate 10 years
after treatment, and that as long as branches were less than 5 cm (2 in.) in diameter and were pruned
flush with the bark, “lumber defects” commonly associated with natural pruning (unsound stubs,
ingrown bark, loose knots and pockets of decay) did not occur.
Sugar Maple
Of the fourteen major commercial tree species examined for the existence of stem-defect/age
relationships in the Ontario decay survey (Basham and Morawski 1964), sugar maple was unique in its
relatively high incidence of defect in immature trees. Table 13 shows that in trees 21 to 60 years of age,
an average of 14.8% of the merchantable stem volume was defective, much higher than in any other
species at comparable stages of maturity. However, Table 13 also shows that, above age 100 years, the
increase in extent of defect levelled off, defect accounted for 26.2% of the merchantable stem volume in
age class 81-100 years and increased only to 32.3% by age class 221-240 years. In the 3,922 sugar maple
trees sampled, 80% of the defect was in the form of stain, a figure exceeded only by that for black ash
(84%). Most of the defect in sugar maple less than 60 years old was stain; very little was decay. Because
sugar maple and yellow birch occur so frequently together, comparisons of the extent of defect in stems
of the two species are of interest. The decay survey data indicate that stem decay and stain are more
extensive in sugar maple up to age 80, but in trees more than 100 years old, they are less extensive than
in yellow birch. When only stem decay is considered, there is little difference in the extent of decay (on
the basis of percentage of stem volume) in the two species before age 90 years (Fig. 19). However, as
trees pass that age, yellow birch quickly develops more decay than sugar maple, and after 180 years,
yellow birch has almost twice as much stem decay as sugar maple.
Table 13. Occurrence of decay and stain in the stems of 3,922 sugar maple sampled in the Great LakesSt. Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
21-60 408
38.9
5.75
1.3
14.8
61-80 696
90.4
18.81 2.3
20.8
81-100
858
218.7 57.29 3.5
(%)
26.2
defective
101-120
537
453.2 111.96 2.7
24.7
121-140
399
532.0 145.25 4.5
27.3
141-160
290
881.9 268.95 6.9
30.5
161-180
252
920.7 267.91 7.0
29.1
181-200
172
1,026.5 318.23 8.8
31.0
201-220
143
1,087.2 352.25 7.6
32.4
221-240
91
1,284.7 414.94 7.9
32.3
241+
1,554.1 559.50 10.1
76
36.0
Figure 19. Comparison of the extent of decay in the merchantable stem portions of yellow birch and
sugar maple trees at similar ages. Decay-age data obtained from curves in Basham and Morawski’s
(1964) figure 27.
Beyond age class 81-100 years, the extent of stain in sugar maple stems remained at between 22 and
25% of the merchantable stem volume, whereas the percentage of decay continued to increase slowly.
The result was that there was less stem defect in mature and overmature sugar maple than in most of
the other deciduous species included in the decay survey (Basham and Morawski 1964). With less than
6% of the merchantable stem volume decayed in trees under age 140, and only about 8% at 240 years
(Table 13), it is clear that stem decay will generally have little impact, regardless of the age at which
sugar maple stands are harvested, and that considerations other than the development of decay will
generally determine cutting ages. Furthermore, the average extent of stain is 22.5% in trees more than
80 years old, regardless of age (Table 13). In most cases, therefore, there is no such thing as a
pathological rotation age for sugar maple.
Nordin (1954) carried out a major study of sugar maple decay in Ontario in basically the same regions as
the federal-provincial decay survey of the 1950s. He examined 606 trees, and although he described
stem stains and the microorganisms isolated from them, he did not include stained wood in his
measurements of stem defect. In comparable age classes, he reported stem decay at roughly double the
percentages of stem volume that were reported in the provincial decay survey. Although his sample size
was much smaller than that of Morawski et al. (1958), it is highly unlikely that the actual difference in
the extent of decay was of that magnitude. A more reasonable explanation is that, because of the
subjectivity involved in distinguishing between stain and early incipient decay, Nordin categorized some
of the defect that Morawski et al. classified as stain under incipient decay. In any case, Nordin’s results
were similar to those of Morawski et al. in that he found the extent of “decay” surprisingly high in his
youngest age class, which he gives as 40 years; from that point on, the extent of decay increased at a
relatively slow rate until about age 220 years. Nordin examined 21 trees more than 300 years old, and
reported a relatively rapid increase in the extent of decay from age 220 years to age 320 years. In the
decay survey, only one tree more than 275 years old was sampled and, consequently, only the beginning
of this trend at about age 240 years was detected.
The decay survey of sugar maple in the federal-provincial study of the 1950s was carried out in the
Algoma and Algonquin ecological sections (Halliday 1937) of the Great Lakes-St. Lawrence Forest Region.
The 784 trees sampled in the Algoma section exhibited appreciably lower average growth rates than the
3,138 trees sampled in the Algonquin section. For example, sugar maple sampled in the Algoma section
at age 140 years averaged 22.5 cm (8.9 in.) DBH in comparison with 141.5 cm (15.9 in.) for trees in the
Algonquin section. Attempts to relate the development of stem decay in sugar maple to site
characteristics were made separately in each ecological section; however, no relationships of any
practical importance were evident (Morawski et al. 1958).
The sample of 3,922 sugar maple was also divided by land type. All 784 trees sampled in the Algoma
ecological section, and 2,831 of the 3,138 trees sampled in the Algonquin section, grew on land of the
Sherborne type. The remaining 317 trees of the Algonquin section grew on land of the Limerick type.
These land types are based on parent soil material and are defined by Hills (1952) as silty-sand till
derived from granitic bedrock (Sherborne) and sandy till derived from basic igneous rock or schists in
which limestone may or may not be present (Limerick). Practically all of the Limerick sample was located
in the easternmost sample plots, near where the three counties of Renfrew, Frontenac and LennoxAddington meet. The Limerick land type has somewhat richer soils than the Sherborne land type. Within
the Algonquin ecological section, the sugar maple sampled on the Limerick land type, in comparable
diameter classes, had somewhat better height growth and a corresponding slightly greater volume than
those on the Sherborne land type (Morawski et al. 1958). The Limerick trees also had a slightly lower
incidence of stem decay. A comparison of maple of similar diameters on the Sherborne land type
indicated that trees in the Algoma section were somewhat more defective than trees in the Algonquin
section.
The two studies of sugar maple decay in the 1950s, those by Nordin and the federal-provincial decay
survey, were carried out in Ontario on the Canadian Shield. Because of the deeper, richer soils south of
the Shield it was generally believed the sugar maple there were faster growing and less defective than
trees growing on the Shield. An opportunity to test this belief arose in the early 1970s in connection
with a thinning and fertilization study carried out by the Great Lakes Forestry Centre (Sault Ste. Marie) in
two typical sugar maple stands in Sydenham Township, Grey County. The thinning involved the felling of
300 sugar maple trees ranging in DBH from 8.9 to 45.7 cm (3.5 to 18 in.), and subsequent bucking into
lengths that corresponded as closely as possible to those in a commercial operation. The average age of
the 300 trees was 65 years, the average DBH was 21.6 cm (8.5 in.), and an average of 4.5% of the
merchantable stem volume was decayed or stained (Basham 1973a). At a comparable age (65 years) in
the federal-provincial decay survey, sugar maple on the Shield had an average DBH of 14 cm (5.5 in.) and
approximately 20% of their merchantable stem volume was defective. These results confirm the belief
that sugar maple south of the Canadian Shield in Ontario tends to be much faster growing and less
defective than sugar maple on the Shield.
Most of the respondents to the questionnaire sent to hardwood-processing industries in southern
Ontario, 70 out of 95, handled sugar maple (Basham 1973a). Twenty-eight of these (35.4%) reported
that stain and decay in this species were serious problems. However, this includes 11 who indicated that
problems were en-Avg. countered only in sugar maple that was grown “to the north”, presumably on
the Canadian Shield. Some of the remainder could well have experienced the same situation but did not
indicate this in their replies. Indeed, in view of the distances between logging sites and manufacturing
plants, it is quite possible that in all problem cases in the three districts bordering the Canadian Shield
(i.e., Lake Simcoe, Lindsay, and Tweed), much of the defective hard maple was cut on the Shield. Replies
from the Lake Huron District suggest a higher-than-average incidence of stain and decay in hard maple
growing on lowland sites in the Bruce and northern Grey counties. Only two of the 31 respondents who
dealt with hard maple in Lake Erie District regarded stain and decay as serious problems in this species.
Nordin (1954) reported a good correlation between sugar maple tree diameter and the loss of
recoverable stem volume attributable to decay and other natural defects. The percentage of
merchantable stem volume decayed increased from 5.6% in the 5-in. (13 cm) diameter class to 18.4% at
26 in. (66 cm). The increase in diameter was accompanied by a gradual, progressive increase in the
percentage of stem volume decayed (Nordin 1954). A similar relationship between sugar maple
diameter and the extent of stem defect was found in the federal-provincial decay survey (Morawski et
al. 1958).
As has already been pointed out, 80% of the stem defect in the 3,922 sugar maple trees studied in the
federal-provincial decay survey was in the form of stain. Approximately 88.5% of the decay was in the
advanced stage and roughly 20% of the decay was in the butt region. Just under 25% of the stain was in
the butt region.
Stained (discolored) sugar maple stem wood frequently occurs in the central portion of the bole where
there is no decay (Fig. 20a). This is not true heartwood in that it is almost invariably the result of a
disturbance such as a dead branch, mechanical wound or fungal invasion. Where fungal decay occurs, it
is surrounded by a collar of stained wood radially and by tapered, stained columns vertically. Most sugar
maple stain is brown, ranging from pale yellowish-brown to dark chocolate brown, but it may also be
greenish-brown, olive green, dark green, or almost black. The term “blackheart” is sometimes used to
describe the chocolate-brown to black stains. All stains, but more particularly those with a greenish hue,
are sometimes called mineral stain. Since the darker stained wood frequently has a higher mineral
(calcium, potassium and magnesium carbonate) content than clear wood and is harder than clear wood
(Scheffer 1954), the term mineral stain is not entirely inappropriate.
Figure 20. Sugar maple stem defects. (a) transverse section of central core of stained wood, (b)
transverse section of advanced decay caused by Polyporus glomeratus, (c) transverse and radial sections
of decay caused by P. glomeratus, (d) transverse section of advanced decay caused by Pholiota
spectabilis (Gymnopilus spectabilis), (e,f) transverse sections of advanced decay caused by Fomes
igniarius (Phellinus igniarius).
The development of stain in sugar maple trees in response to an injury or infection can be regarded as a
defence mechanism on the part of the tree, a modification of the affected tissue to make it less suitable
for, and therefore more resistant to, invasion by microorganisms, particularly decay fungi; for this
reason, it is sometimes referred to as protection wood. Much of the stain is apparently sterile; in
another study, 948 isolation attempts were made in 209 sugar maple trees from stained wood
containing no decay, and 62.3% proved to be sterile (Basham and Taylor 1965). Fungi were isolated in
30.8% and bacteria in 6.9% of the cases. In the same sample of 209 trees, 83 isolation attempts were
made from stained wood associated with decay; 47% of these were sterile, 49.4% yielded fungi and
3.6% yielded bacteria. Most of the fungi were non-decay fungi that are not believed to be capable of
causing discoloration. Clearly, stain in sugar maple is primarily of physiological, not pathological, origin in
most cases. In some cases stain does harbor decay-causing fungi; approximately 25% of the isolations of
the decay fungus Polyporus glomeratus (renamed Inonotus glomeratus) from the 3,922 sugar maple
sampled in the decay survey were obtained from stained wood. Although some of those stains may have
developed as early incipient P. glomeratus decay, it seems likely that in most cases the stain was present
before it was invaded by the fungus.
Roughly 70% of the decay encountered in the 3,922 sugar maple examined in the federal-provincial
decay survey was a yellow-brown stringy type that occurred in both trunk and butt regions. In the trunk,
the main causal organism was P. glomeratus (Fig. 20b,c), followed by Pholiota spectabilis (renamed
Gymnopilus spectabilis [Fig. 20d]). In the butt region, yellow-brown stringy decay was caused mainly by
Armillaria sp. (probably A. ostoyae) and P. spectabilis. About 20% of the stem decay was a white spongy
type in both the trunk and butt regions. This decay was caused by Fomes igniarius (renamed Phellinus
igniarius [Fig. 20 (e,f)]) and Fomes connatus (renamed Oxyporus populinus). The appearance of F.
igniarius decay has been described in the section on trembling aspen. Decay caused by F. connatus is
similar in appearance, but is more greyish-white and does not have black zone lines. Incipient yellow
decay accounted for most of the remaining 10% of the stem decay in the 3,922 sugar maple, from which
several fungi were isolated; the most common of these was P. glomeratus. A very small amount of
brown cubical butt decay, caused by Coprinus micaceus and Poria cocos (renamed Wolfiporia extensa),
was encountered.
In both the federal-provincial decay survey, in which 3,922 sugar maple were examined (Basham and
Morawski 1964), and in Nordin’s (1954) study, in which 606 sugar maple were examined, P. glomeratus
was isolated from stem decay with far greater frequency than any other decay fungus. It accounted for
34% of the isolations of decay fungi in the former study and 25% of such isolations in the latter. In both
studies, the fungus that ranked second in frequency of isolation was Corticium vellereum (renamed
Hypochnicium vellereum). Unlike other decay fungi, which gain entrance to the stem almost exclusively
through stem wounds or broken tops, C. vellereum also enters through branch stubs, where it causes
decay and is an inhabitant of the stained wood that develops in the stem from branch stubs (Basham
and Anderson 1977). Corticium vellereum was isolated repeatedly from stain and from decay of all types
in sugar maple, with the exception of brown cubical decay. It is generally believed that C. vellereum,
though a member of the class Basidiomycetes, to which 99% of stem and root decay fungi belong, is
incapable of causing advanced decay in sugar maple stems. Its presence in decays and stains of all types
probably reflects its ability to invade stained wood or wood already decayed by other fungi.
In his study of stem decay in 606 sugar maple trees in south-central Ontario, Nordin (1954) attempted to
identify the entry point for each decay column or pocket. He concluded that the most common entry
points, in order of frequency, were frost cracks, dead branches and stubs, stem scars (felling, lightning,
fire, etc.) and root systems. More than 90% of decay infections could be traced to those sources. Other
entry points included damaged tops, cankers, burls and parent stumps. Nordin did point out that,
whereas branch stubs were frequent entry points, the volume of decay associated with each stub was
relatively small. In a study of 1,024 sugar maple branch stubs on 275 second-growth trees, Basham and
Anderson (1977) concluded that branch stubs were an insignificant source of stem decay. However,
although the upper age limit of the trees was 114 years, no stubs with diameters larger than 5.1 cm (2
in.) were available for sampling. Six of the 1,024 stubs yielded isolates of P. glomeratus and one yielded
F. igniarius. When seven larger stubs (average diameter 7.4 cm) on four larger trees were subsequently
examined, decay pockets caused by P. spectabilis were found in three of them. In yet another study in
south-central Ontario, Vasiloff and Basham (1963) examined 455 second-growth sugar maple and
concluded that decay fungi entered stems through stem wounds rather than through branch stubs, with
very rare exceptions. From careful examination of what appeared to be frost cracks, they concluded that
the majority were originally “felling scars or sun scald injuries that were followed by repeated separation
of the callus, presumably due to sudden temperature changes, resulting in frost ribs” (Vasiloff and
Basham 1963).
Shigo (1966) found that decay in sugar maple stems entered through logging wounds, and that F.
connatus, the most common decay fungus in this association, was present in four of the 48 trees
studied.
Although a few of the fungi that decay sugar maple produce sporophores on the stems of living trees or
nearby on the ground, the sporophores are either inconspicuous, short-lived, or both. An exception is
Fomes igniarius, whose sporophores are long-lived and very conspicuous; however, they are rare on
living trees. These fruiting bodies have been described in the section on trembling aspen. When they do
occur on living sugar maple, decay generally extends at least 2 m above and below the sporophores.
Fomes connatus sporophores are sometimes produced on the edges of basal stem wounds. They are
small, generally less than 3 cm wide, soft, and yellowish-white, and frequently have green moss growing
on their tops. The volume of internal decay associated with F. connatus sporophores is usually quite
small. Armillaria sp. sporophores have been described in the section on trembling aspen. They form on
the base of stems or on the ground nearby, but are short-lived and occur only in late summer or early
fall. Polyporus glomeratus very seldom produces sporophores on living trees, but the presence of stem
decay is sometimes indicated by swollen, punky knots or linear black seams formed by the fungus. A
small proportion of the white spongy trunk decay in sugar maple is caused by the fungus Hydnum
septentrionale. This fungus is mentioned here because its few occurrences are generally revealed by
prominent clusters of creamy-white, fleshy, shelf-like sporophores with the undersurface covered with
white spines. Their presence usually indicates extensive stem decay.
The most reliable external indicators of stem decay in sugar maple are stem wounds or other
abnormalities, and the size and age of those abnormalities. Branch stubs or dead branches more than 5
cm (Basham and Anderson 1977) or 10 cm (Hesterberg 1957) in diameter are likely entry courts for stem
decay. Little defect is associated with branch stubs less than 2.7 cm (0.5 in.) in diameter. Stubs between
these sizes, though associated with little or no decay, can be responsible for the introduction of
considerable stain into the core of the stem, particularly those stubs that heal relatively slowly and are
near the upper end of the size range (Basham and Anderson 1977).
Vasiloff and Basham (1963) found stem wounds to be the most reliable indicators of the extent of stem
decay in Ontario. They reported that sunscald injuries and felling scars, followed by frost cracks and
dead leaders, were associated with the largest volume of decay. Other common types of wound
associated with stem decay were fire scars, cankers caused by the fungus Eutypella parasitica, skidding
scars, and narrow seams of uncertain origin. Less common types of wound associated with decay were
broken tops, broken crotches and branch-stub seams. Ohman (1968a) found the most reliable external
indicators of stem decay in sugar maple in the United States to be abnormal bole swellings or
depressions, mechanical wounds, cracks, seams, holes, unhealed branch stubs, fungal sporophores,
cankers, bird pecks and insect holes. Lavallée (1968) listed mechanical injuries, frost cracks, and large
broken branches as the most reliable signs of decay in sugar maple in Quebec. He also noted that the
size of the injury was related to the volume of decay. In a study of sugar maple deterioration after
logging damage in the Lake States, Hesterberg (1957) reported that logging wounds narrower then 10
cm (4 in.) had far less associated stem decay 20 years later than scars wider than 20 cm (8 in.), which
frequently hid extensive decay. Basal scars caused by either skidding or felling have been shown to
cause more butt decay when in contact with the ground than when not in contact with the ground
(Anon. 1973). The same report indicated that exposed, light-colored wound surfaces usually have very
limited stem decay, whereas darker surfaces usually indicate extensive decay. Two abnormalities that
are fairly common on sugar maple stems in south-central Ontario, cankers caused by E. parasitica and
irregular, deep lesions caused by the sugar maple borer, Glycobius speciosus, are associated with a
limited amount of internal stem defect (decay in the former case, but primarily stain in the latter). They
also signal a risk of stem breakage at the point of disfigurement.
The many research studies carried out on the development of stain and decay in sugar maple stems
have formed the basis for several recommended silvicultural and management practices that can
appreciably reduce their impact. Because much of the stem stain enters through unhealed branch stubs,
any practice that promotes self-pruning when the trees are relatively young and vigorous and the
branches small will minimize stain development. Clearly, this is preferable to young, relatively opengrowing stands in which most self-pruning occurs decades later, after crown encroachment, when the
branches are large; at this point, tree vigor is declining and healing of stubs is very slow. Though labor
intensive and therefore costly, artificial flush pruning of vigorous selected crop trees, concentrated on
live branches less than 5 cm (2 in.) in diameter to promote rapid healing, has been shown to improve
tree quality with no reduction in tree growth rate (Skilling 1958; Zeedyk and Hough 1958).
Sugar maple stand decadence can be reduced by the removal of high-risk trees, i.e., those with the most
serious external indicators of stem decay, as early as is possible in conjunction with other practices. In
most cases, stem decay that arises from stem wounds is forever confined to a central column of a
diameter equal to that of the tree at the time of wound infliction. Therefore, a stem wound on a large
tree is potentially much more serious than a wound on a small tree. In the latter case, prevention of
further injury and promotion of a satisfactory growth rate should result in a crop tree with a very small
proportion of defective stem wood.
The incidence of many stem wounds of the type that result in the most stem decay can, to a great
extent, be minimized by modifying management procedures. Sunscald wounds are caused by frost injury
induced by warming of the bark by the sun on the southwestern side and subsequent rapid cooling at
night. Partial cutting to avoid drastic reductions in basal area largely eliminates sunscald hazards in
residual trees. Forest-fire prevention and careful logging supervision to reduce logging damage to the
residual trees are other steps that can be taken to reduce the impact of stem decay. Finally, harvesting
stands before they become overmature will obviously reduce somewhat the extent of decay in sugar
maple logs. The observation that “harvest ages of 80 to 120 years for saw-timber are feasible on most
sites under good management” (Ohman 1968b), though aimed primarily at forest managers south of the
border, should also be appropriate for most sugar maple stands in Ontario.
Other Maples
The provincewide decay survey of the 1950s was carried out on the Canadian Shield, on which silver
maple is relatively rare and black maple almost never occurs; this explains why these two species were
not sampled. Red maple is more common than silver maple on the Shield, and 66 red maple trees were
sampled in the decay survey. This sample was considered too small to provide meaningful stem-decay
relationships, and it was not included in the two publications that dealt with the survey (Morawski et al.
1958; Basham and Morawski 1964). However, because of the scarcity of information on red maple stem
decay, results obtained from the 66 trees are presented herein.
The 66 red maple were widely scattered throughout the Algoma and Algonquin ecological sections.
Usually only one or two trees larger than the minimum sampling size grew in each plot, and for the most
part red maple was a minor component of stands composed mainly of sugar maple, yellow birch, beech
and hemlock. Table 14 shows that, at comparable ages, red maple stems were considerably more
defective than those of sugar maple, and somewhat more defective than those of yellow birch. In age
class 101-120 years, the average merchantable volumes for red maple, sugar maple, and yellow birch
were 348, 453 and 464 dm3, respectively; the approximate average percentages of those volumes that
were defective were 40, 25 and 30%, respectively.
Table 14. Occurrence of decay and stain in the stems of 66 red maple sampled in the Great Lakes- St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Age class
Avg. defective Merch. vol.
No. of merch. (decay and stain)
Merch. vol.
decayed
defective
(years) trees
vol. (dm3)
41-60 15
82.1
16.25 1.0
19.8
61-80 18
144.4 40.69 7.2
28.6
81-100
9
209.5 91.80 18.6
43.8
101-120
11
348.3 140.35 12.3
40.3
121-140
5
444.6 207.14 8.1
46.6
141+
767.5 397.61 19.2
8
vol. (dm3)
(%)
(%)
51.8
Although the sample was small, the data in Table 14 show that, in red maple, the percentage of
merchantable stem volume affected by decay and stain increased with age, and averaged more than
40% after age 80 years. Decay accounted for 31 % of the defect in red maple in comparison with 20% in
sugar maple. Stem decay apparently begins at a relatively early age in red maple. Table 14 shows that
7.2% of stem volume was decayed in the 18 trees in age class 61-80 years, in comparison with only 1.6%
in yellow birch (Table 12) and 2.3% in sugar maple (Table 13) in the same age class.
Stained wood in red maple stems was medium- to dark-brown and occurred alone in the central core or
at the boundaries of decay columns. Most of the decay (88.5%) was of the advanced yellow-brown
stringy type, mainly in the trunk but also fairly common in the butt region. Smaller amounts of white
spongy decay, virtually limited to the trunk region, and of incipient yellow-brown decay in both trunk
and butt regions, were found in the stems of the 66 red maple sampled.
The principal decay fungus in red maple stems in Ontario, as it is in sugar maple, is Polyporus glomeratus
(renamed Inonotus glomeratus). This fungus is associated with most of the yellow-brown stringy trunk
decay and occasionally with the same type of butt decay. Some isolations of P. glomeratus were
obtained from brown trunk stains, which were most likely early incipient stages of P. glomeratus decay.
A small proportion of the yellow-brown stringy trunk decay was caused by Stereum murraii (renamed
Cystostereum murraii) and Pholiota spectabilis (renamed Gymnopilus spectabilis). The yellow-brown
stringy butt decay was caused primarily by Armillaria sp. (probably A. ostoyae), P. spectabilis and
Pholiota aurivella. The relatively small amount of white spongy decay found in red maple was caused by
Fomes igniarius (renamed Phellinus igniarius). Virtually the same fungi have been reported as the causes
of most stem decay in red maple in the northeastern United States (Campbell and Spaulding 1942; Shigo
1965b), except that those authors also report that Fomes connatus (renamed Oxyporus populinus) is a
major cause of decay in that region.
Stem decay in silver maple has never, to my knowledge, been intensively studied in Ontario. However,
Eslyn (1962) used nondestructive methods (radiation and increment cores) to detect decay and to
identify decay-causing fungi in silver maple stands in Iowa. Because of the techniques used, his results
were confined to the lower stem regions. The most frequently isolated Basidiomycete was Corticium
vellereum (renamed Hypochnicium vellereum), which Eslyn suspected was not a primary cause of decay.
Only one other decay-causing fungus was consistently isolated, P. aurivella, which Eslyn described as of
major importance in butt decay of silver maple.
Of the 95 hardwood-processing industries south of the Canadian Shield in Ontario that responded to the
stem-defect questionnaire, 66 indicated that they handled soft (red or silver) maple (Basham 1973a). Of
those, 30 (45.5%) indicated that they had serious decay and stain problems with those species, which
made soft maple the number-one problem in that respect. The major problem with soft maple,
according to the questionnaire respondents, was “wormy wood” or “worm holes”. Follow-up visits to
sawmills revealed that the “worm holes” were small tunnels 1to 2 mm in diameter that appeared to
occur anywhere throughout the xylem, from the pith to the cambium. These were invariably surrounded
by a fairly extensive greenish-brown stain that formed a more-or-less star-shaped pattern on the faces
of cut logs. One or more species of ambrosia beetle, probably including the genera Xyloterinus and
Corthylus, are responsible for the tunnels. Apparently the insects can invade and damage healthy,
vigorous trees. The stain is probably caused by the fungi carried into the tree and used as food by the
beetles.
Although “wormy” soft maple was by far the most frequently noted defect in this species group, some
respondents reported the occurrence of butt decay. However, from comments on the questionnaire
replies and from visits to southern Ontario mills, it was concluded that this is seldom a serious problem
except in overmature trees or stands.
A study of decay in 324 red maple connected to 72 clumps of sprouts in New Hampshire revealed that
branch stubs were far more important as entry points for decay fungi than were parent stumps (Shigo
1965b). The principal decay fungus that infected trees through branch stubs was Polyporus glomeratus.
Logging wounds in red maple have been shown to serve as points of entry to the stem for Fomes
igniarius, Fomes connatus and Corticium vellereum (Shigo 1966).
Sound, or relatively sound, red maple trees are valuable. However, because they are subject to
considerable stem stain and decay at a relatively early age (Table 14), early pruning (natural or artificial)
followed by rapid growth and harvesting well before age 100 years should help to prevent stem decay
from having a serious economic impact.
Beech
One of the principal reasons beech is generally considered a low-value tree species is because it is
thought to be highly defective. In the federal-provincial decay survey of the 1950s, 393 beech were
sampled, all in the Algonquin ecological section. The percentages of merchantable stem volume affected
by decay and stain are shown, by age class, in Table 15. The beech sample was about as defective as the
sugar maple sampled in the survey (Table 13), and less defective than yellow birch (Table 12) and red
maple (Table 14). Hence, on the basis of the decay survey, beech is certainly no worse than average in
comparison with other tolerant hardwood species of south-central Ontario as far as stem defectiveness
is concerned.
Table 15. Occurrence of decay and stain in the stems of 393 beech sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
41-60 19
23.5
3.31
0.9
14.1
61-80 80
61.7
12.90 7.1
20.9
81-100
99
110.9 31.47 10.0
28.4
101-120
69
298.2 63.79 6.7
21.4
121-140
57
663.4 222.92 9.3
33.6
141-160
38
1,007.0 368.53 13.0
36.6
161+
1,671.3 655.09 18.9
31
(%)
defective
39.2
Roughly 10% of beech stem volume was decayed after trees reached approximately 70 years of age
(Table 15). The extent of defect increased gradually with age until trees reached 140 years; from this age
onward, between 10 and 20% of the stem volume was decayed and close to 40% of the volume was
defective.
Replies to a questionnaire were received from 63 hardwood industries that processed beech in Ontario
south of the Canadian Shield; of these, 23 (36.5%) indicated that stem decay and stain were serious
problems (Basham 1973a). Soft maples were the only species for which a higher percentage of
respondents showed concern. In beech, decay alone was considered a serious problem by 33% of the
respondents, by far the highest percentage of any species. The decay was frequently described by
respondents as butt decay, and occasionally as a trunk decay associated with rough, swollen bark or
with numerous branch stubs.
The percentage of merchantable stem volume that was defective in the 393 beech sampled increased
consistently with tree diameter (Morawski et al. 1958). Most of the trees grew as patchy admixtures in
sugar maple/yellow birch stands on dry and fresh sites, primarily on upper slopes. The sample was too
small for an analysis of the relationship between site and stem defect. However, it was observed that
most defect tended to occur in beech growing on dry, shallow soils (Morawski et al. 1958).
Beech grown in Ontario south of the Shield is generally of poor quality and is utilized only sparingly by
the wood-using industries of that region. Besides the fact that there is a reluctance to use beech for
many products, once a tree is cut the logs are susceptible to relatively rapid development of sap stain. In
addition, the lumber has a tendency to shrink, check, and warp unless dried very carefully. Nevertheless,
beech is present in most stands and woodlots in southern Ontario, often as a major stand component. It
is perhaps significant that one-third of those respondents who processed or dealt with beech felt that
stain and/or decay were serious problems. This suggests that those respondents, at least, believe that
beech is potentially of some commercial value.
The stained stem wood in the 393 beech sampled in the federal-provincial decay survey was brownish
and accounted for 63.6% of the defect in this species. This is a comparatively low figure for tolerant
hardwoods in the Great Lakes-St. Lawrence Forest Region of Ontario. Fully one-quarter of the stain
occurred in the butt region. Stained wood was occasionally the only stem defect, particularly in the
younger trees. More commonly, it surrounded decay pockets or columns in narrow bands radially and in
tapered extensions vertically.
About 84% of the decay was in the advanced stage, and the most common type of advanced decay was
a yellow-brown stringy type that occurred in both trunk and butt regions of the stems. Most of the
remaining advanced decay was white and spongy, and was found in both trunk and butt regions. A very
small amount of brown cubical butt decay was found. The remaining decay was an incipient yellow type
that occurred almost entirely in the trunk region.
Polyporus glomeratus (renamed Inonotus glomeratus) was the principal cause of stem decay (usually a
yellow-brown stringy trunk type) in beech. Yellow-brown stringy butt decay was caused by Armillaria sp.
(probably A. ostoyae) and by Pholiota aurivella (often incorrectly identified as P. adiposa before 1965).
Most of the white spongy trunk and butt decay was caused by Fomes igniarius (renamed Phellinus
igniarius). Corticium vellereum (renamed Hypochnicium vellereum) and P. glomeratus were the fungi
most frequently isolated from the incipient yellow decay and from brown stain.
In New Hampshire, Campbell and Davidson (1939) observed that P. glomeratus infected beech primarily
through dead branch stubs, but also occasionally through stem wounds. Logging wounds have been
shown to serve as entry points to beech stems for F. igniarius, P. aurivella, Armillaria sp. and several
other decay fungi (Shigo 1966). The size of the logging wound was a fairly accurate indicator of the
extent of internal defect in this species. Extensive P. glomeratus trunk decay in beech frequently results
in bark swellings or cankers, and at branch stubs black, roughened fungal material that protrudes as
much as 7.5 cm (3 in.), frequently called “sterile conks”, may appear (Campbell and Davidson 1939).
The results of the federal-provincial decay survey of the 1950s indicated that, at least on the Canadian
Shield, the reputation of beech as a relatively defective species is largely undeserved. Because beech
was almost always bypassed in logging operations in the past, many overmature or wounded, and
therefore defective, beech are growing in our forests today. If care is taken to avoid wounding young
beech during logging operations and if the trees are harvested before the age of 130 years, two-thirds of
the stem, on average, should be free of decay and stain (Table 15).
Basswood
Only 140 basswood of merchantable size were present in the sample plots established in the federalprovincial decay survey of the 1950s. This relatively small sample formed the basis for Table 16, which
indicates that basswood is one of the least defective deciduous tree species in Ontario. Table 16
indicates that very little decay or stain is present in basswood stems until age 120 years, and although
the conclusion is based on relatively few sample trees, it is probably safe to assume that basswood
harvested before age 120 years will not have extensive stem defect. The few (29) trees sampled that
were older than 120 years, on the other hand, were quite defective.
Table 16. Occurrence of decay and stain in the stems of 140 basswood sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
21-40 9
30.4
0.66
0.0
2.2
41-60 33
89.9
2.70
0.4
3.0
61-80 37
490.3 19.10 1.8
3.9
81-100
22
776.8 36.52 3.5
4.7
101-120
10
1,128.5 50.78 2.8
4.5
121-140
12
1,883.2 374.78 15.6
19.9
141-180
11
2,349.4 540.33 10.0
23.0
181+
2,896.6 915.34 23.9
6
(%)
defective
31.6
The majority of the 140 sampled basswood occurred in sugar maple/yellow birch stands in the southern
portion of the Algonquin ecological section, on good sites with deep, loamy soils and fresh-to-moist
moisture regimes. There was insufficient variation in site among the trees sampled for an analysis of the
relationship between site and the extent of stem defect.
Replies to a questionnaire were received from 63 hardwood industries that processed basswood south
of the Canadian Shield in Ontario. When the apparent relative soundness of basswood on the Shield is
considered, it came as a surprise that 16 of the respondents (25.4%) indicated serious basswood decay
and stain problems (Basham 1973a). In terms of defects, this ranked basswood fourth among the 12
hardwood species covered in the questionnaire. Stem stain was identified as the problem by six of the
respondents, whereas the other 10 reported that both stain and decay were cause for serious concern.
Basswood had the lowest (25.4%) percentage of stem defect in the form of stain of all the deciduous
trees in Ontario that were sampled in the federal-provincial decay survey. The stain was generally
brownish, occasionally with a green hue. All of the decay was either yellow-brown stringy advanced
decay or incipient yellow decay. Yellow-brown stringy advanced decay made up two-thirds of the total
defect volume in basswood and was present in both butt and trunk regions.
Pholiota aurivella (often incorrectly identified as P. adiposa before 1965) caused much of the decay in
the 140 basswood sampled (Basham and Morawski 1964). It, along with Pholiota spectabilis (renamed
Gymnopilus spectabilis), caused practically all of the trunk defect. Armillaria sp. (probably A. ostoyae)
was the cause of most of the yellow-brown stringy butt decay; P. aurivella was also responsible for some
of the butt defect.
There are virtually no reliable external indicators of stem defect in basswood except in late summer and
early fall, when the short-lived fruiting bodies of Armillaria, P. aurivella, and P. spectabilis may appear.
Little is known about the entry of these decay fungi into basswood stems; however, it appears likely that
some of the stem decay can be attributed to the fact that basswood regenerates by producing sprouts
from the base of old stumps. The evidence in Table 16 indicates that the only procedure necessary to
ensure that stem decay and stain do not become serious is to harvest basswood before, or soon after, it
reaches age 120 years.
Black Ash
Table 17 shows the occurrence, by age class, of decay and stain in the relatively small sample of 103
black ash trees sampled in the federal-provincial decay survey of the 1950s. The fact that a very high
percentage (62 to 75%) of stem volume is affected by decay and stain in trees more than 100 years old is
tempered somewhat by the fact that most of this defect is in the form of stain. Indeed, the presence of
stain almost throughout the merchantable length of the oldest trees suggests that much of the stain is
true heartwood, and is a result of the normal process and death of cells rather than a result of wounding
(branch death, etc.) or trauma such as invasion by fungi or insects. Nevertheless, the very extensive stain
in the stems of the 35 black ash that were more than 100 years old suggests that, where discolored
wood is objectionable, this species should be harvested by, or soon after, age 100 years. The incidence
of decay, as shown in the second-last column of Table 17, is comparable with that in other tolerant
hardwood species of Ontario.
Table 17. Occurrence of decay and stain in the stems of 103 black ash sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
41-60 24
50.8
3.8
61-80 30
151.5 28.18 6.0
2.23
4.4
18.6
(%)
defective
81-100
14
295.8 67.12 3.6
22.7
101-120
9
402.7 249.24 2.3
61.9
121-140
12
810.4 605.39 14.9
74.7
141+
1,395.3 1,046.47
14
11.3
75.0
Black ash sampled in the decay survey was confined largely to moist and wet sites (Morawski et al. 1958)
in the Algonquin and Algoma ecological sections. Replies to a questionnaire were received from 70
hardwood industries in southern Ontario south of the Canadian Shield that process ash (Basham 1973a).
These indicated that stem decay and stain in ash were not serious problems in that region.
About 84% of the defect encountered in stems of black ash was in the form of stain. All stain in ash was
medium to dark brown; it was present in both butt and trunk regions, and was particularly extensive in
older trees. Most of the advanced decay was a yellow-brown stringy type, and occurred mainly in the
trunk region; the remainder was white, spongy decay in both branch and butt regions. A small amount
of incipient yellow decay was also encountered in the stems of black ash.
Unlike in most other tree species in Ontario, no single fungus stood out as the most common cause of
stem decay in black ash. Stereum murraii (renamed Cystostereum murraii) and Polyporus glomeratus
(renamed Inonotus glomeratus) caused most of the yellow-brown stringy trunk decay, and Armillaria sp.
(probably A. ostoyae) caused most of the yellow-brown stringy butt decay. White spongy decay was
caused mainly by Fomes igniarius (renamed Phellinus igniarius) and Fomes conchatus (renamed
Phellinus conchatus).
Red Oak
Red oak is far more abundant, and therefore a far more valuable resource, in the United States than in
Ontario, or in Canada for that matter. Hence, practically all of the research and literature on red oak
stem decay and stain originates in the United States. Only 42 red oak were present on sample plots of
the federal-provincial decay survey of the 1950s. The extent of stem decay and stain in the stems of
these trees, by age class, is shown in Table 18. Though a relatively small sample, it nevertheless indicates
that stem defect in red oak is not a serious problem. Minor amounts of decay and stain were present in
the 34 trees between the ages of 40 and 140 years that were sampled. Decay was moderately extensive
in the eight sampled trees more than 140 years old, but stain was relatively sparse. The red to reddishbrown normal heartwood of red oak was quite distinct from the wound-initiated brown stain, and was
not included in Table 18.
Table 18. Occurrence of decay and stain in the stems of 42 red oak sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
41-60 9
144.4 2.87
0.0
2.0
61-80 22
232.3 8.83
0.7
3.8
81-140
3
141+
8
947.1 63.44 2.0
1,500.9 199.60 8.4
(%)
defective
6.7
13.3
Replies to a questionnaire were received from 55 hardwood industries that processed red oak south of
the Canadian Shield in Ontario. Only six of the respondents reported serious decay or stain problems, an
indication that stem decay and stain in red oak are not serious problems in southern Ontario (Basham
1973a).
From American reports it appears that red oak stem decay is not a serious problem south of the border
either. In fact, the title of one United States Forest Service paper published in Pennsylvania is “Decay not
serious in northern red oak” (Berry and Beaton 1971). In a study of stem decay in five oak species in
Kentucky, Berry (1969) found that only 0.65% of the volume of red oak stems was decayed. The
percentages of stem volume that were decayed in three of the species of oak were 2.66, 2.35 and
1.84%. Only white oak, with 0.75% decayed, was less defective than red oak.
The brown stain in the 42 red oak sampled in the federal-provincial decay survey appeared to originate
in branch stubs, and comprised only 13% of the total defect volume. All of the decay was in the
advanced stage, and fully 98% was the advanced yellow-brown stringy type, which occurred in both butt
and trunk regions. Small amounts of white spongy trunk decay and brown cubical butt decay were also
encountered. Decay and stain together amounted to only 6.3% of the total merchantable volume of the
42 sample trees.
Data from the decay survey on the identity of the fungi causing decay in the sample of 42 red oak in
Ontario were insufficient to justify their inclusion in this report. In several American studies, fungi that
cause decay in red oak have been identified. From those reports it is clear that several different fungi
are responsible for roughly equal proportions of stem decay. Since the majority of them cause little or
no stem decay in other tree species in Ontario, there is no need to name them in this report. In one
other study carried out in Ontario, near Petawawa, Riley (1947) reported that Polyporus obtusis
(renamed Spongipellis unicolor) caused considerable stem decay of red, white and bur oaks in some
areas. This fungus was not isolated from the 42 red oak sampled in Ontario in the 1950s, and is rarely
mentioned in reports from the United States that deal with stem decay in oak.
In American studies of stem decay in red oak and other oaks, the two major points of entry for decaycausing fungi appear to be basal fire scars and dead branch stubs.
White Elm
In the federal-provincial decay survey carried out in the 1950s, 62 white elm were sampled; it was felt
that this sample was too small to provide meaningful stem-decay relationships and this species was not
included in the two publications that dealt with that survey (Morawski et al. 1958; Basham and
Morawski 1964). The data on stem decay and stain collected from those 62 trees are presented in Table
19. From this table it is clear that neither decay nor stain is a serious problem in white elm until trees are
well over 100 years old.
Table 19. Occurrence of decay and stain in the stems of 62 white elm sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
41-60 26
59.5
0.9
61-80 13
107.6 13.87 1.0
81-100
10
121+
13
3.68
6.2
12.9
478.6 67.98 1.9
1,612.8 688.68 5.6
(%)
defective
14.2
42.7
Most of the stem defect (84.6%) in the 62 white elm was a brown stain. An advanced yellow-brown
stringy decay, which occurred mostly in the butt region, accounted for more than half of the decay
volume. A white, spongy trunk decay and an incipient yellow trunk decay were also encountered in
white elm. The major cause of decay was Pholiota aurivella (often incorrectly identified as P. adiposa
before 1965), which was responsible for most of the yellow-brown stringy decay. Much of the remaining
decay was caused by Pleurotus ulmarius.
Black Cherry
Because the species is rare on the Canadian Shield in Ontario, only 22 black cherry trees of
merchantable size were present in the sample plots established for the federal-provincial decay survey
of the 1950s. Of course, no relationships between the extent of stem decay and stain in these trees and
age, diameter, site, etc., can be assessed from such a small sample. Nevertheless, because black cherry
is a valuable species commercially, the information obtained from the 22 trees is presented as an
indication of how much, and what types of, defect can be expected in black cherry stems in southcentral Ontario.
Of the 22 trees, three were in the 21- to 40-year age class and one was in the 161- to 180-year class.
With the largest age class (101-120 years) represented by only six trees, it was felt that breaking down
the extent of stem decay and stain by age class in the form of a table would be virtually meaningless.
However, there was the usual trend of increasing stem defect, as a percentage of merchantable volume,
with increasing age. The extent of stem decay in the 22 black cherry was greater than the average for
tolerant hardwood species in south-central Ontario. The three trees in the 21- to 40-year age class had
an average of 7% of their stem volume decayed, much more than for trees of any of the other tolerant
hardwood species in the 41- to 60-year age class. The eight trees sampled that were more than 100
years old had an average of 21% of their merchantable stem volume decayed. Because of the normal
reddish-brown heartwood of black cherry, it is difficult to detect pathological or wound-initiated stain
with certainty. It was felt that dark brown stains surrounding decay pockets or associated with dead
branch stubs were not normal heartwood. These comprised roughly 15% of the merchantable stem
volume, on average, with very slight increases with increasing age class.
Replies to a questionnaire were received from 40 hardwood industries that processed black cherry
south of the Canadian Shield in Ontario; only six of those indicated that stem decay was a serious
problem (Basham 1973a). This suggests that black cherry south of the Shield in Ontario may be less
defective than black cherry growing on the Shield.
Decay in the stems of black cherry differed from that in other tolerant hardwoods not only by its
presence at a relatively early age, but in its appearance as well. The greatest volume loss was caused by
a reddish-brown trunk decay that contained scattered, soft white pockets. Brown cubical decay
accounted for much of the remaining decay; it was present in both butt and trunk regions. A limited
amount of advanced yellow-brown stringy decay occurred in both trunk and butt regions of the stem.
Little information was obtained on the identity of the major decay-causing fungi in black cherry from the
22-tree sample. From the few identified isolates, and from the intensive study of black cherry stem
decay carried out in Pennsylvania by Davidson and Campbell (1943), it appears that no single fungus is
the major cause of stem decay in this species. Furthermore, the many fungi that do cause decay are, for
the most part, different from those that cause serious decay problems in the stems of the other
commercially important tree species of Ontario.
Dead branch stubs of relatively large diameter were found to be the main points of entry for decaycausing fungi of black cherry in Pennsylvania (Davidson and Campbell 1943). To reduce the development
of stem decay on a stand basis, they recommended the removal of forked trees and the elimination of
multiple-sprout clumps. In another Pennsylvania study, Grisez (1978) concluded that pruning young
black cherry trees up to about 50% of their total height can increase the quality and value of the trees
thereafter.
Ironwood
Although it is of relatively little commercial value, mainly because of its small size at maturity, ironwood
is widely scattered throughout the Algonquin ecological section of south-central Ontario, and 157 trees
of merchantable size were present in the sample plots of the federal-provincial decay survey of the
1950s. This sample was large enough to yield meaningful decay relationships for this species.
Table 20 reveals that, on the basis of the 157-tree sample, ironwood is a relatively defective species as
far as stem decay and stain are concerned. Of all the species covered in this report, only red maple had
as high a percentage of merchantable stem volume affected by decay as ironwood, in all age classes
sampled. Stained wood, which varied from medium to dark brown, accounted for 62.3% of the defect
volume. The most common type of advanced decay was the yellow-brown, stringy type, which occurred
more in the butt than in the trunk region. White, spongy decay was also present, primarily in the trunk
region. Some brown cubical butt decay was found. An incipient yellow decay was sometimes
encountered in the trunk region, but rarely in the butt region.
Table 20. Occurrence of decay and stain in the stems of 157 ironwood sampled in the Great Lakes-St.
Lawrence Forest Region of Ontario. Based on trees examined as part of the federal-provincial decay
survey of the 1950s.
Avg.
Avg. defective Merch. vol.
Merch. vol.
Age class
No. of merch. (decay and stain)
decayed
(years) trees
vol. (dm3)
vol. (dm3)
(%)
21-60 51
19.8
1.91
1.0
61-80 46
48.4
14.83 9.3
81-100
24
95.2
38.54 12.7
40.5
101-120
18
149.5 52.94 14.3
35.4
121+
237.3 101.43 19.7
18
(%)
defective
9.7
30.6
37.1
The major causes of stem decay in ironwood were Stereum murraii (renamed Cystostereum murraii),
mainly as a yellow-brown stringy trunk decay; Pholiota aurivella (often incorrectly identified as P.
adiposa before 1965), which caused most of the yellow-brown stringy butt decay; and Fomes igniarius
(renamed Phellinus igniarius), the cause of most of the white spongy decay.
Acknowledgments
So many people contributed in various ways to the preparation and substance of this report that it is
impossible to mention all of them. Special thanks are due to George Vasiloff and Wayne Ingram for the
collection of some of the field data and data analyses; to Ed Rayner for processing the photographs; to
the Great Lakes Forestry Centre’s Biometrics and Application Software Services for reproducing the
graphs; to Geoffrey Hart and Constance Plexman for editing the manuscript; and to Dr. Pritam Singh
(Forestry Canada’s Coordinator, Pathology and Entomology) for originally suggesting the concept. The
preparation of a report so comprehensive and detailed would not have been possible without the termemployment program for retired scientists, inaugurated in 1988 by Dr. Jean-Claude Mercier, Deputy
Minister, Forestry Canada.
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Perala, D.
1971. Aspen successfully regenerated after killing residual vegetation with herbicides. USDA For. Serv.,
North Central For. Exp. Stn., St. Paul, Minn. Res. Note NC-106. 2 p.
Prielipp, D.O.
1957. Balsam fir pathology for Upper Michigan. Kimberley-Clark of Michigan, Inc., Mimeogr. Rep. 68 p.
Redmond, D.R.
1957. Infection courts of butt-rotting fungi in balsam fir. For. Sci. 3: 15-21.
Riley, C.G.
1947. Heart rot of oaks caused by Polyporus obtusus. Can. J. Res. C. 25: 181-184.
_________
1952. Studies in forest pathology. IX. Fomes igniarius decay of poplar. Can. J. Bot. 30: 710-734.
Riley, C.G. and Bier, J.E.
1936. Extent of decay in poplar as indicated by the presence of sporophores of the fungus Fomes
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Rudolf, P.O.
1958. Silvical characteristics of jack pine. USDA For. Serv., Lake States For. Exp. Stn., St. Paul, Minn. Stn.
Pap. No. 61. 31 p.
Scheffer, T.C.
1954. Mineral stain in hard maples and other hardwoods. USDA For. Serv., For. Prod. Lab, Madison, Wis.
Rep. No. 1981. 2 p.
Shigo, A.L.
1965a. The pattern of decays and discolorations in northern hardwoods. Phytopathology 55: 648-652.
_________
1965b. Decay and discoloration in sprout red maple. Phytopathology 55: 957-962.
_________
1966. Decay and discoloration following logging wounds on northern hardwoods. USDA For. Serv.,
Northeastern For. Exp. Stn., Upper Darby, Pa. Res. Pap. NE-47. 43 p.
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829-831.
Skilling, D.D.
1958. Wound healing and defects following northern hardwood pruning. J. For. 56: 19-22.
___________
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Spaulding, P. and Hansbrough, J.R.
1944. Decay in balsam fir in New England and New York. USDA, Washington, D.C. Tech. Bull. 872. 30 p.
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1954. Progress of decay in decadent yellow birch trees. For. Chron. 30(3): 292-298.
___________
1955. Decay of yellow birch in Nova Scotia. For. Chron. 31(1): 74-83.
___________
1956. Pathological aspects of severe spruce budworm attack. For. Sci. 2: 174-186.
Strothmann, R.O. and Zasada, Z.A.
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1969. Silvics of white spruce (Picea glauca (Moench) Voss). Dep. Fish. For., Ottawa, Ont. For. Br. Publ.
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1971. Variation in decay in aspen stands as affected by their clonal growth pattern. Can. J. For. Res. 1:
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1953. Studies in forest pathology. X. Decay of white pine in the Temagami Lake and Ottawa Valley areas.
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_________
1960. Insects and diseases and the future of white pine. Timber of Can., December issue. 3 p.
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1976. Root rot of spruce and balsam fir in northwestern Ontario. I. Damage and implications for forest
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___________
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___________
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___________
1979. Minimizing root rot losses in Ontario pulpwood species. Dep. Environ., Can. For. Serv., Sault Ste.
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___________
1988. Root rot: the hidden enemy. Gov’t of Can., Can. For. Serv., Sault Ste. Marie, Ont. 35 p.
___________
1989. Root rot damage in naturally regenerated stands of spruce and balsam fir in Ontario. Can. J. For.
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Whitney, R.D. and Brace, L.G.
1979. Internal defect resulting from logging wounds in residual white pine trees. For. Chron. 55(1): 8-12.
Whitney, R.D. and Denyer, B.G.
1970. Inoculations with Stereum sanguinolentum and Fomes pini in black spruce and balsam fir. For. Sci.
16: 160-164.
Whitney, R.D. and MacDonald, G.B.
1985. Effects of root rot on the growth of balsam fir. Can. J. For. Res. 15: 890-895.
Winget, C.H.
1969. Apparent defect in second-growth tolerant hardwood stands in Quebec. For. Chron. 45(3): 1-4.
Zeedyk, W.D. and Hough, A.F.
1958. Pruning allegheny hardwoods. USDA For. Serv., Northeastern For. Exp. Stn., Upper Darby, Pa. Stn.
Pap. No. 102. 14 p.
Appendix A. Common and scientific names for tree species referred to in the text
Common name Scientific name
Ash, black
Fraxinus nigra Marsh.
Aspen, largetooth
Populus grandidentata Michx.
Aspen, trembling
Populus tremuloides Michx.
Basswood
Tilia americana L.
Beech Fagus grandifolia Ehrh.
Birch, white
Betula papyrifera Marsh.
Birch, yellow
Betula alleghaniensis Britton
Cedar, eastern white
Cherry, black
Thuja occidentalis L.
Prunus serotina Ehrh.
Cottonwood, eastern
Populus deltoides Bartr.
Elm, white
Ulmus americana L.
Fir, balsam
Abies balsamea (L.) Mill.
Hemlock, eastern
Ironwood
Tsuga canadensis (L.) Carr.
Ostrya virginiana (Mill.) K. Koch
Larch, eastern (tamarack)
Larix laricina (Du Roi) K. Koch
Maple, black
Acer nigrum Michx. f.
Maple, red
Acer rubrum L.
Maple, silver
Acer saccharinum L.
Maple, sugar
Acer saccharum Marsh.
Oak, bur
Quercus macrocarpa Michx.
Oak, red
Quercus rubra L.
Oak, white
Quercus alba L.
Pine, eastern white
Pinus strobus L.
Pine, jack
Pinus banksiana Lamb.
Pine, red
Pinus resinosa Ait.
Poplar, balsam Populus balsamifera L.
Spruce, black
Picea mariana (Mill.) B.S.P.
Spruce, white Picea glauca (Moench) Voss
Appendix B. Decay-causing fungi referred to in the text, with proposed or accepted new nomenclature
Name generally used between
World War II and the early 1960s
Corticium galactinum
Proposed or accepted new name
Scytinostroma galactinum
Corticium polygonium Peniophora polygonia
Corticium vellereum
Hypochnicium vellereum
Flammula alnicola
Pholiota alnicola
Fomes conchatus
Phellinus conchatus
Fomes connatus
Oxyporus populinus
Fomes igniarius
Phellinus igniarius
Fomes igniarius var. laevigatus Phellinus laevigatus
Fomes igniarius var. populinus Phellinus tremulae
Fomes pini
Phellinus pini
Odontia bicolor
Resinicium bicolor
Merulius himantioides Serpula himantioides
Pholiota adiposa
Pholiola aurivella
Pholiota spectabilis
Gymnopilus spectabilis
Polyporus balsameus
Tyromyces balsameus
Polyporus glomeratus Inonotus glomeratus
Polyporus obtusis
Spongipellus unicolor
Polyporus schweinitzii Phaeolus schweinitzii
Polyporus tomentosus Inonolus pseudopini
Poria cocos
Wolfiporia extensa
Stereum murraii
Stereum pini
Cystostereum murraii
Peniophora pseudopini
Stereum sanguinolentum
Haematostereum sanguinolentum
Appendix C. Calculations used by Basham and Morawski (1964) to estimate timber and revenue losses in
Ontario as a result of stem decay.
Tables 76 and 77 present the results of calculations designed to give some indication of the economic
importance of heartwood defects of fungal origin to the forest industry of Ontario. They are based on
the three most recent Annual Reports of the Minister of Lands and Forests of the Province of Ontario
(13, 14, 15). These reports contain summaries of the volume of each species cut annually, based on
measurements of the timber following deductions for defect made in accordance with the Ontario
scaling regulations. Measurements are recorded in different units depending upon the product, and all
units are converted into equivalent cubic feet. Table 76 shows the average annual net volume of timber
cut, in cubic measure calculated in this way, for the twelve major commercial tree species of Ontario in
this period (April 1, 1958 to March 31, 1961). Although arbitrary measurements based on scaling
regulations frequently do not coincide with various utilization practices or with manufactured volumes,
they represent a universally recognized standard with which other yields can be compared.
Table 76. The average annual volume cut and revenue from crown stumpage charges for the 12 major
commercial tree species of Ontario from 1 April 1958 to 31 March 1961.
Average annual Percentage of Average annual Percentage of
net volume cut total annual
revenue
Species (thousand ft3) net volume cut (thousand $)
Black spruce
137,066
41.5
5,137 44.3
Jack pine
74,505 22.6
2,118 18.3
total annual
revenue
White spruce
41,438 12.5
1,593 13.7
White pine
19,825 6.0
1,121 9.7
Yellow birch
6,845 2.1
514
4.4
Balsam fir
12,935 3.9
284
2.5
Red pine
4,935 1.5
269
2.3
Sugar maple
4,759 1.4
183
1.6
18,619 5.6
182
Trembling aspen
Hemlock
3,198 1.0
81
0.7
White birch
1,516 0.5
26
0.2
Basswood
384
0.1
22
0.2
and fuelwood 4,262 1.3
57
0.5
1.6
Other species
Total
330,287
100.0 11,587 100.0
Table 77. Theoretical annual loss of revenue in Crown stumpage charges as a result of heartwood
defects of fungal origin in the 12 major commercial tree species of Ontario.
A, Percentage
Theoretical
of volume
B, Percentage
defective
Factor for
volume Revenue
revenue lost
of volume
Selected
culled as a
at felling age
value per
converting
as a result
felling age
thousand ft3
(curved
of defect
from
Species (years) values) A to B age
(thousand $)
Estimated
Average
culled at
felling volume cut
annual
Estimated
annual
annual net
annual gross
volume cut
result of defect
(thousand ft3) (thousand ft3) (thousand ft3) ($)
Yellow birch
140
35.4
0.845 29.9
6,845 9,765 2,920 75
219
White pine
120
9.8
1.606 15.7
19,825 23,517 3,692 57
210
Black spruce
120
2.9
1.238 3.6
137,066
White spruce
110
3.5
1.300 4.6
41,438 43,436 1,998 38
76
Jack pine
90
2.4
1.270 11
74,505 76,889 2,384 28
67
Sugar maple
140
28.5
0.744 21.2
4,759 6,039 1,280 38
49
Balsam fir
80
7.0
1.259 8.8
12,935 14,183 1,248 22
27
Trembling aspen
70
16.4
Hemlock
140
5.5
2.146 11.8
3,198 3,626 428
25
11
Red pine
100
1.0
1.606 1.6
4,935 5,015 80
55
4
Basswood
110
5.0
1.289 6.4
384
26
57
2
White birch
80
6.5
0.400 2.6
1,516 1,556 40
17
1
Average
-
-
-
6.3
-
-
-
Total
-
-
-
326,025
-
0.731 12.0
142,185
5,119 37
18,619 21,158 2,539 10
410
-
-
347,779
21,754 -
189
25
880
The annual revenue from Crown stumpage charges, by species and product, is also summarized in these
reports. The average annual revenue for each of the twelve principal tree species is shown in Table 76.
Stumpage charges vary among different species, and within species according to the product and
location. Of course, they are much less than market values, but are directly related to them. Hence, the
revenue values for each species shown in Table 76 bear roughly the same relationship to one another as
do the market values of the annual cut of each species in Ontario.
Table 77 shows the theoretical annual loss of revenue in Crown stumpage charges due to heartwood
defects of fungal origin in the twelve major commercial tree species of Ontario. In this table for each
species ages were selected that were considered most likely to approximate average harvest ages. For
each species the percentage of the total merchantable volume defective at these ages has been
ascertained from balanced curves prepared from the final columns in the series “B” tables. These
percentages were then converted to percentages representing volumes culled according to the Ontario
scaling regulations. A conversion factor of 1.606 for white pine was obtained from the data presented by
White (16), and, since red pine has such similar defects and uses, the same factor was applied to both
species. For the remaining species, cull volumes for the same samples had been calculated (10), so that
conversion factors were easily computed.
For each species, the average annual net volume cut (Table 76) and the percentage of the volume culled
at the estimated harvest ages were now available. From these, it was a simple matter to compute the
annual gross volume cut, and the annual volume culled due to defect. The latter amounted to
approximately 22 million cubic feet, or 6.3 per cent of the former.
The revenue value per thousand cubic feet of timber for each species was derived from Table 76. By
multiplying these values by the annual volumes culled, figures were obtained which represent additional
revenue that theoretically could have been obtained from each species had these culled volumes been
free of defect. This amounted to $880,000 annually for the twelve major species, of which three-fourths
was attributable to only three species, namely, yellow birch, black spruce, and white pine.
Top Rot In Glaze-Damaged Black Cherry And Sugar Maple On The Allegheny Plateau
Research
Journal of Forestry
W. A. Campbell and Ross W. Davidson, Civilian Conservation Corps and Division of Forest Pathology,
Bureau of Plant Industry
REF# 393
Black cherry and sugar maple damaged in a glaze storm in 1936 were examined 40 and 48 months
respectively after the storm to determine the extent of visible decay. It is believed that the common
wound parasites which caused most of the top rot in cherry will eventually die and the wounds heal.
Black cherry 3 inches in diameter or less at the break is considered to be a good risk for saw timber
production, provided the breaks are confined to the branches and the upper part of the main stem and
are accompanied by vigorous crown regeneration.
The glaze storm of March 1936 caused considerable damage to second-growth hardwoods on the Kane
Experimental Forest and elsewhere in northern Pennsylvania and southern New York. Downs made a
survey of glaze damage on the Kane Experimental Forest and found that 21.5 percent of the hardwoods
in the 21-40 year age class were damaged and that 16.9 percent were damaged severely. Black cherry
(Prunus serotina Ehrhart) was damaged more than any other species chiefly because of its dominant
position in the stands and consequent coarse branchy crowns. Approximately 59 percent of 2,180 black
cherries examined had top breakage and 41 percent were damaged severely. As would be expected the
severity of damage increased with the age and size of the trees.
Nineteen months, after the storm Sleeth examined a limited number of top wounds in living black
cherry and found that white decay had progressed from 3 to 24 inches in the heartwood below the
breaks. The average downward extent of visible decay was 14.0 inches. Isolates from 25 specimens were
mainly Polyporus versicolor Fr. and Stereum rameale Schw. His data suggested that considerable decay
might result from top wounds in black cherry and that the ultimate loss would depend upon the ability
of the above-mentioned fungi, or those that supersede them, to cause heartwood decay.
In August 1939, approximately 40 months after the 1936 storm, 191 top wounds in 66 black cherries
were examined for extent of visible decay. These trees were mostly 40 to 50 years old and were growing
on the Kane Experimental Forest, near Kane, Pa. In addition 94 top wounds in sugar maple (Acer
saccharum Marshall) of the same age were examined 48 months after the storm in order to compare
the type and extent of decay with those in black cherry. The fungi associated with decay were
determined by pure-culture methods.
Cross sections of black cherry tops at or below the breaks showed the decay to be concentrated for the
most part in the heartwood between the sound center and the sound outermost rings of the heartwood
in what were the innermost rings of sapwood at the time of injury (Fig. 2, A). In a number of wounds the
entire exposed heartwood was decayed at or near the surface. The decay column in most cases
diminished rapidly with the distance from the break and finally became a thin water-soaked or
discolored streak (Fig. 2, B). The downward extent of visible decay varied considerably and averaged
23.5 inches for all breaks. The average extent of decay (Fig. 1) increased with the diameter of the broken
top or limb and was slightly over 30 inches for breaks in the 4.1-5 inches diameter class and larger.
Figure l. Average extent of decay in glaze-damaged black cherry after 40 months and sugar maple after
48 months in relation to diameters of broken tops. Numeral at each point indicates number of breaks on
which it was based. Solid line, black cherry; broken line, sugar maple.
Figure 2. A, cross section of black cherry stem 4 inches below top wound showing distribution of decay.
B, longitudinal section showing downward distribution of decay form top wound in black cherry. C,
decay from top wound in sugar maple. D, Stereum rameale sporophores on exposed wood of top wound
in black cherry.
A measure of the downward progress of decay in black cherry can be had by comparing the average
extent of decay from Sleeth’s data with that from the present study. Sleeth’s data gave the average
extent of visible rot from 24 breaks 4 inches in diameter or less as 13.8 inches. The average for the
same-size wounds from the present study was 21.0 inches, indicating a slowing down of decay between
19 months and 40 months after damage.
Decay from top breaks under 5 inches in diameter in sugar maple was limited to 6 inches or less from
the break (Fig. 1) and was concentrated chiefly in the oldest wood at the center of the wounds (Fig. 2,
C). The lower limits of decay were usually bordered by a greenish discoloration which extended several
inches beyond visible decay. These sugar maples 40 to 50 years old did not have heartwood and decay
was definitely limited to the wound area.
Practically all top wounds in black cherry and sugar maple were infected by white rot fungi. In a number
of wounds the decay appeared inactive and gave nondecay producing fungi or bacteria from decay
samples. Decay fungi obtained from 86 percent of 152 black cherry decay samples and as shown by
Table 1 these were mainly Polyporus versicolor and Stereum rameale. S. rameale sporophores were
common on the exposed wood of both large and small wounds (Fig. 2, D). P. versicolor was less
frequently noted. Sporophores of other decay fungi were rare. Most of the decay associated with top
wounds in sugar maple was inactive and insect riddled. Decay isolations were attempted from maple
from only 31 of the 94 wounds examined. Nine of these gave P. versicolor; 3, P. hirsutus (Wulf.) Fr.; 3,
Hypoxylon sp.; and 4, unidentified decay fungi. Twelve gave nondecay producing fungi. P. versicolor, P.
hirsutus, and Hypoxylon sp. were occasionally observed fruiting on the exposed wood or dead bark of
top wounds.
Table 1. Organisms Isolated From Top Rot In Glaze-Damaged Black Cherry
Number
Percent
of times
of total Percent of
Organism
isolated
isolations
Polyporus versicolor
78
51
59
Stereum rameale
27
17
20
9
10
.6
.7
decay fungi
P. versicolor
and S. rameale in
same wound
14
P. pargamenus 1
Unidentified decay
fungi 12
7
Total decay fungi
9
132
86
20
14
--
Nondecay producing
fungi and bacteria
It is believed that the common wound parasites, such as P. versicolor and S. rameale which caused most
of the top rot in cherry will eventually die as the wounds heal. Decay from top wounds 3 inches in
diameter or less in black cherry should be limited to 2 or 3 feet below the break, and to less than 6
inches for wounds in sugar maple. Such trees are good risks for saw timber production provided the
breaks are confined to the branches and upper part of the main stem and are accompanied by vigorous
crown regeneration. On the other hand, large wounds which dry on the surface and are not thoroughly
decayed by saprophytes may eventually become infected by typical heartrotters. Therefore, trees with
badly splintered or shattered tops are poor risks for saw timber and should be utilized in 10 to 15 years.
Freeze/Thaw
Sunscald/Exposure
Ice Damage
Interim Guidelines for the Tapping and Restoration of Sugar Bushes Affected by the Ice Storm of January
1998
Extension
Ontario Ministry of Agriculture, Food and Rural Affairs , Ontario Ministry of Natural Resources
Dave Chapeskie, Cathy Nielsen
February 1998
REF# 010
Introduction
This guideline was developed through consultation with a team of maple and other forestry specialists
from Ontario and the United States. It is an interim guideline for the 1998 season. A revised guideline
which incorporates the results of a full review of research, practical experience, and the results of
monitoring in 1998 will be issued for the 1999 season.
Due to the severity of tree damage, both short-term and long-term losses in the production potential of
sugar bushes damaged by ice are expected. However, it is anticipated that while some trees will be lost
to mortality, many others will survive even in the moderate to severe damage classes. Survival of the
damaged trees will depend on a number of factors:
1.
The health and condition of the trees before and at the time of the ice storm.
2.
The degree of damage suffered (e.g. condition of the bole, percent loss of live crown, size of
branches lost, etc.)
3.
The age and vigor of the trees.
4.
The productivity of the site.
5.
Future weather conditions, especially over the next few years. For example, a prolonged
summer drought could slow recovery and cause increased mortality.
6.
Other future adverse biological and environmental conditions that could place further stress on
the damaged trees (e.g. insect defoliation, grazing of cattle, overtapping, mechanical damage to root
systems and stems, etc.)
Expected Response of Sugar Maple to Ice Storm Damage
1.
Although trees have suffered loss of crowns, it should be remembered that a large proportion of
the tree is represented by the root system which is still intact in all but uprooted trees.
2.
Damaged trees have an altered root/shoot ratio in favour of roots because of the loss of
branches. This should result in food reserves being available to compartmentalize or wall off and isolate
damaged areas to prevent diseases from spreading from injuries to healthy areas.
3.
Sugar maple has a moderate ability to regrow its crown after pruning. With the loss of live
crown, dormant buds on the existing branches will be activated leading to the development of new
branches. Healthy trees growing on well drained fertile soils will have the greatest potential to reestablish their crowns, heal wounds and ward off insects and diseases.
4.
Damaged branches and increased sunlight on large branches and the main stem may lead to the
development of epicormic branches. These small branches are usually found on the bole of the tree and
on large branches.
5.
The increased exposure of the trees to sunlight and wind may increase sunscald damage.
6.
The increased sunlight coming down through the main canopy will accelerate the growth of
both desirable and undesirable understory vegetation. Retaining even severely damaged trees for 3 to 5
years will help to reduce the invasion of undesirable understory vegetation.
7.
Broken branches and other freshly exposed wood are infection sites for decay fungi which may
infect trees and contribute to tree decline. The extent of decay and decline will not be known for some
time, therefore monitoring tree condition will be important.
8.
The damage caused by ice is not expected to lead to serious insect infestations in sugar maple
stands. However, populations of the most destructive pests (e.g. sugar maple borer, forest tent
caterpillar) should be closely monitored.
9.
Sap will drip from broken branches in the crown but this is not expected to have a substantial
effect on sap yields or the healing process.
Operational Guidelines for the Clean-Up and Restoration of Sugarbushes Affected by Ice Accumulations
1.
For sugar bushes which are accessible to the public, post a sign to warn of potential dangers
related to the condition of the trees (e.g. weak limbs, loose stems, broken branches, etc.)
2.
In all cases, sugar bush owners should wait for the trees to de-ice before they access the
damage and begin clean-up operations.
3.
Be aware of the danger posed by loose limbs and weak stems when working in the bush. Wear
appropriate safety equipment (e.g. hard hats, steel toe boots, etc.). A reduction in the amount of snow
and ice on the ground will lessen the safety hazards associated with working in the bush.
4.
Consult with a forest resource professional (forest technician, forester, arborist, etc.) when
completing damage assessments and deciding on a course of action. Reference should be made to
these guidelines.
5.
Restoring road access, restoring access into the sugar bush and repairing or replacing lines
must be completed in a timely manner if tapping is to be feasible in 1998. Care should be taken to
ensure that the tubing system is restored following proper installation procedures.
6.
In 1998, after the sap season, emphasis should be placed on removing only the most severely
damaged trees (e.g. those with entire loss of crown, uprooted trees and those which are safety hazards).
It is felt that all but the most severely damaged trees as noted should be retained throughout
the spring and summer of 1998, since it is believed that many trees will survive including many of those
with considerable crown loss.
Special emphasis should be placed on monitoring tree condition and growth response during
the spring and summer of 1998.
By leaving the trees over the spring and summer, it will be possible to observe individual tree
condition and response at the end of the 1998 growing season. Signs of declining health are cankers,
conks, open wounds, early discolouration of foliage, and small leaf size.
Further removal of severely damaged trees that are not doing well should be considered based
on their condition in the fall of 1998. Contacting a forest resource professional (forestry technician,
forester) for advice on tree removal is highly recommended.
7.
Careful logging practices are recommended so that damage to tree stems and root systems is
minimized. Logging and excessive traffic in the sugar bush during the spring break-up period should be
avoided. In addition to the potential for damage to stems, rutting caused by tractors and skidders will
damage root systems placing further stress on affected trees. Wounding of the stem and root systems
will provide infection sites for decay fungi. This type of wounding could be more damaging than the ice
storm because soil contact wounds are more susceptible to infection.
8.
Consider individual tree damage level, individual tree age and vigor, site quality and other
important stand and site factors in the decision making process leading to the restoration of sugar
bushes affected by the ice storm.
9.
Logging debris which is not merchantable and /or is not a barrier to access should be retained
on site. Material larger than 10 cm (4 inches) in diameter should be lopped to within 60 cm ( 24 inches)
from the ground. This debris will biodegrade over a period of time and will contribute to the
productivity of the site.
10.
Amended guidelines will be issued in the fall of 1998 which will take into account the response
of individual trees to varying levels of loss of live crown during the spring and summer period.
11.
If you are considering doing some pruning, be sure to use proper pruning techniques. These are
described in the Landowner Resource Centre Extension Note entitled, “Caring for Ice Damaged Trees”.
Assessing Storm Damage in Your Maple Bush
The following assessment system is divided into two sections. Section I is a method for assessing
individual trees to determine which trees should still be tapped and how many taps should be used.
Section II explains a method to assess your bush for overall damage and to obtain an estimate of taps
based on degree of damage and application of the tapping recommendations for ice damaged maple
trees.
Section I: Individual Tree Assessment
When assessing a tree, try to visualize what the full crown looked like before damage and estimate how
much of the crown is left. The reason for basing the assessment on the crown remaining is that we tend
to over estimate the damage when focusing on the amount of crown missing.
Crown damage is then calculated by subtracting this number from 100. For example: A sugar maple tree
has 60% of the original crown left, therefore, it has 40% damage and would fit into the moderate crown
damage class.
It is recommended that you assess the trees with another person; with two opinions to average out any
bias your estimate will be more reliable.
Crown Damage Class
Light
0-11%
Moderate
11-50%
Heavy 50-75%
Severe >75%
Once you have determined the Crown Damage Class, use the tapping guideline for damaged trees
outlined in Table 1.
Table 1. Recommendations for Tapping Spring 1998 for Storm Damaged Sugar Bushes
Recommendations for tapping individual trees in the spring of 1998 related mainly to percentage of
crown loss and the probability of the tree surviving.
Amount of
Damage
Recommendations
Crown Loss
Class
0-10% light
tap as usual using
Rationale
Normal tapping recommended as the extent
traditional or general
of damage is minimal and unlikely to affect the
tapping guidelines
trees survival. Tree survival should be good
(See guideline 1 below.)
11-50% moderate
tap using the conservative
The more conservative tapping rule is
recoguidelines for stressed trees
mmended to minimize further stress on trees.
Depending on nature of damage, growing
conditions etc. the trees should survive.
(See guideline 2 below.)
50-75% heavy tapping is not recommended
These trees will hopefully survive but some
may be borderline. All energies of these
trees should be directed towards survival,
compartmentalization and callusing of wounds.
Over 75%
survive. Their
severe tapping is not recommended
unless trees are identified for
Trees with severe crown loss may
survival will depend on a number of factors
such as
such as removal in 1998 age, site, growing
conditions and the occurrence of adverse
biological and or environmental conditions over the
next few years. If there is a high percentage of
trees in your sugar bush in this category, serious
conditions should be given to not tapping your
sugar bush in 1998.
Guideline 1: Traditional or General Tapping
Diameter of tree measured outside bark,
4 ½ feet above the ground
less than 10”
0
10” - 14”
1
15” - 19”
2
Number of Tapholes per Tree
20” - 24”
3
25” and larger 4
Guideline 2: Conservating Tapping for Stressed Trees
Diameter of tree measured outside bark,
Number of Taps
4 ½ feet above the ground
less than 12”
0
12” - 18”
1
18” +
2
Section II: Determining the Number of Taps in a Damaged Stand
The objectives of the following assessment are:
1.
Determine overall damage to maple trees in the sugar bush.
2.
Obtain an estimate of the number of taps based on degree of damage and application of the
tapping guidelines for ice damaged maple trees.
Assessment to Determine Damage and Tapping Potential of Sugar Bush for 1998:
Step 1. Mapping Compartments
If you have a map of forest compartments, use this as a reference to record damage. If you do not have
a forest compartment map, draw a simple map that shows areas that differ in species, composition,
age, stocking and vertical stand structure as separate compartments. If the sugar bush is relatively
uniform, it can be treated as one compartment.
Step 2. Sample three locations (plots) in each compartment
Repeating the assessment of a sample of trees in three locations (plots) distributed within the
compartment will give a more reliable estimate.
Step 3. Assessing a sample of trees - a plot
Select a point to begin your assessment. It should not be near a road or close to the edge of the stand
since these areas tend to have more damage and will give a biased assessment of the whole bush.
Try to select a point that is representative of the conditions in a majority of the compartment you are
assessing.
From your starting point select the closest maple that is greater than 25 cm (10 inches) DBH. Record
the crown damage class as described in the individual tree assessment section. Select the next closest
maple. Continue in this manner until you have assessed 10 trees. Repeat the procedure for two
additional plots for a total of three plots in a compartment. (See Table 2).
Table 2. Tree Assessment Record Form
Compartment 1
For each tree assessed record the following information:
DBH (in.)
Taps
Crown Damage Adjusted Taps
Class
Plot #1
1
16
2
mod
1
2
16
2
mod
1
3
18
1
mod
0
4
18
1
light
1
5
8
0
light
0
6
18
1
light
1
7
24
3
mod
2
8
24
3
mod
2
9
8
0
-
0
10
24
3
mod
2
1
16
1
light
1
2
24
3
mod
2
3
22
3
mod
2
4
16
1
light
1
5
16
1
light
1
6
16
2
mod
1
7
24
3
mod
2
Plot #2
8
22
2
light
2
9
16
2
mod
1
10
16
2
mod
1
1
18
1
light
1
2
24
3
mod
2
3
24
3
mod
2
4
8
0
-
0
5
24
3
mod
2
6
16
2
mod
1
7
16
2
mod
1
8
18
1
mod
0
9
18
1
light
1
10
8
0
light
0
52
Total Adjusted Taps
Plot #3
Total Taps
34
Step 4. Maple Bush Summary
If you had more than one compartment the next step would be to total the Normal Taps and Adjusted
Taps over all compartments.
Normal Taps
Compartment 1 52
Adjusted Taps
34
(seeTable 2)
Compartment 2 48
30
(no example)
100
64
Step 5. Calculating the percent of original taps remaining
64/100* 100 = 64%. Using the level of damage in the example bush above and the tapping
recommendations for ice damaged trees you would have 64% of the original number of taps for the
bush (before the storm).
Step 6. To calculate the number of taps for the bush:
Percent taps for damaged bush * number of taps for bush before storm = number of taps for storm
damaged maple bush
Therefore, if you had 3000 taps in the bush before the storm
.64 * 3000 = 1920 taps
This assessment indicates that you will have 1920 taps based on this degree of damage and the
application of the tapping recommendations for ice damaged maple trees.
Complete Assessment:
The Quick Assessment will also assist in the decision to do a more detailed assessment at a later date.
Additional information will be needed to decide on future management activities in your sugar bush: for
example, how much damage to polewood and sapling size trees and how much damage to other tree
species in your woodlot.
Decisions to cut specific trees should be delayed until you have a chance to assess the impact of the
damage over the next growing season. The exception to this is any trees that poses a safety hazard.
Guidelines for a complete assessment will be published in the near future.
References
1.
Caring for Ice Damaged Trees. 1998. Landowner Resource Centre. Manotick, Ontario.
2.
Houston, D.R.; Allen, D.C.; Lachance, D. 1990. Sugarbush Management: A Guide to Maintaining
Tree Health; North Eastern Forest Experiment Station, General Technical Report NE-129.
3.
Coons, C.F. 1992. Sugarbush Management for Maple Syrup Producers. Ministry of Natural
Resources.
4.
North American Maple Syrup Producers Manual. 1996. Produced by Ohio State University
Extension in Cooperation with the North American Maple Syrup Council.
Lignes directrices provisoires concernant l'entaillage et le rétablissement des érables endommagés par
la tempête de verglas de janvier 1998
Extension
Le ministère de l'Agriculture, de l'Alimentation et des Affaires rurales et le ministère des Richesses
naturelles de l'Ontario
Dave Chapeskie, forestier professionnel inscrit
Cathy Nielsen, Spécialiste de la biodiversité forestière
Février 1998
REF# 396
Introduction
Les présentes lignes directrices provisoires pour 1998 ont été élaborées en consultation avec une équipe
de spécialistes de l'érable et d'autres spécialistes forestiers de l'Ontario et des États-Unis. Les lignes
directrices qui seront publiées pour la saison 1999 seront révisées en fonction des résultats d'un examen
complet des recherches, de l'expérience pratique et des contrôles effectués.
En raison de la gravité des dommages causés aux arbres, on peut escompter une baisse immédiate et à
long terme de la production potentielle des érablières touchées. Certains arbres mourront, mais
d'autres survivront même s'ils ont subi des dommages modérés ou graves. La survie des arbres
endommagés reposera sur un certain nombre de facteurs :
1.
Santé et état des arbres avant et pendant la tempête de verglas;
2.
Gravité des dommages (p. ex., état du fût, pourcentage de perte de la couronne, taille des
branches perdues, etc.);
3.
Âge et vigueur des arbres;
4.
Productivité du site;
5.
Conditions météorologiques futures, particulièrement au cours des prochaines années. Par
exemple, une sécheresse estivale prolongée ralentirait le rétablissement et aggraverait la mortalité;
6.
Autres conditions biologiques et environnementales défavorables qui feraient subir un stress
supplémentaire aux arbres endommagés (p. ex., défoliation par des insectes, animaux qui broutent,
entaillage inconsidéré, dommages aux systèmes radiculaires et aux tiges dus à des actions mécaniques,
etc.).
Réaction prévue de l'érable à sucre aux dommages causés par la tempête de verglas
1.
Bien que la couronne des arbres ait été endommagée, le système radiculaire, qui représente
une bonne partie de l'arbre, demeure intact sauf chez les arbres déracinés.
2.
Les arbres endommagés présentent un rapport système radiculaire/système foliacé déséquilibré
en faveur des racines en raison de la perte de branches. Des réserves alimentaires pourraient ainsi être
disponibles pour contenir et isoler les parties endommagées afin d'éviter que des maladies ne se
propagent des blessures aux parties saines.
3.
L'érable à sucre a une capacité modérée de rétablir sa couronne après l'élagage. La perte de
couronne vivante activera des bourgeons dormants sur les branches, ce qui entraînera la pousse de
nouvelles branches. Les arbres sains se trouvant sur des sols fertiles et bien drainés seront les plus
susceptibles de rétablir leur couronne, de guérir de leurs blessures et de résister aux insectes et aux
maladies.
4.
Des branches endommagées et une hausse de l'ensoleillement des grandes branches et du tronc
peuvent donner lieu à des pousses adventives. Ces petites branches se trouvent généralement sur le fût
et les grandes branches de l'arbre.
5.
L'exposition accrue des arbres au soleil et au vent peut aggraver les dommages causés par
l'insolation.
6.
L'intensification de la lumière qui traverse le couvert accélérera la croissance des plantes
désirables et indésirables de l'étage inférieur. Pour contenir la prolifération des plantes indésirables, il
est souhaitable de maintenir les arbres sur pied pendant trois à cinq ans, même ceux qui sont très
endommagés.
7.
Les branches brisées et le bois fraîchement mis à nu exposent les arbres aux champignons de la
carie, qui peuvent contribuer au dépérissement des arbres. La gravité de la carie et du dépérissement
ne pourra être établie dans l'immédiat; il faudra donc surveiller l'état des arbres.
8.
Les dommages causés par le verglas ne devraient pas entraîner de graves infestations par des
insectes dans les peuplements d'érables à sucre. Cependant, il est souhaitable de surveiller étroitement
les populations des insectes nuisibles les plus destructeurs (p. ex., perceur de l'érable, livrée des forêts).
9.
De la sève s'écoulera des branches brisées de la couronne, mais ce phénomène ne devrait pas
nuire à la production de sève ni au processus de guérison.
Lignes directrices opérationnelles pour le déblaiement et le rétablissement des érablières endommagées
par l'accumulation de glace
1.
Dans les érablières accessibles au public, installez une affiche informant des dangers pouvant
découler de l'état des arbres (p. ex., branches fragiles, lâches ou brisées, etc.).
2.
Les propriétaires d'érablières devraient attendre que la glace tombe des arbres avant d'évaluer
les dégâts et d'entreprendre le déblaiement.
3.
En travaillant dans l'érablière, prenez garde aux branches lâches et fragiles. Portez des
vêtements de sécurité (p. ex., casque, bottes à embout d'acier, etc.). Moins il y a de neige et de glace au
sol, moins l'érablière présentera de risques.
4.
Consultez un spécialiste de la forêt (technicien en sylviculture, aménagiste, arboriste, etc.) au
moment d'évaluer les dommages et de déterminer les mesures à prendre. Consultez également les
présentes lignes directrices.
5.
Pour que l'entaillage soit possible en 1998, rétablissez l'accès routier et l'accès à l'érablière et
réparez ou remplacez les tubulures le plus tôt possible. Assurez-vous d'installer correctement les
tubulures.
6.
Une fois la collecte terminée en 1998, n'abattez que les arbres les plus gravement endommagés
(p. ex., ceux qui ont perdu toute leur couronne, les arbres déracinés et ceux qui posent un danger).
Conservez les autres arbres pendant le printemps et l'été 1998, car on croit que bon nombre
d'entre eux survivront, y compris de nombreux arbres qui ont perdu une grande partie de leur
couronne.
Pendant le printemps et l'été 1998, la priorité devrait être accordée à la surveillance de l'état et
du taux de croissance des arbres.
En laissant les arbres sur pied pendant le printemps et l'été, il sera possible d'observer l'état et
le taux de croissance des différents arbres à la fin de la saison de croissance de 1998. Parmi les signes
de dépérissement, relevons le chancre, l'amadou, les blessures ouvertes, une décoloration précoce du
feuillage et des feuilles de petite taille.
À l'automne 1998, envisagez d'abattre les arbres très endommagés qui ne semblent pas se
rétablir. Il est fortement recommandé de consulter un spécialiste de la forêt (technicien en sylviculture,
aménagiste) au sujet de l'abattage.
7.
Il est recommandé d'utiliser des méthodes prudentes d'exploitation forestière pour éviter
d'endommager les fûts et systèmes radiculaires des arbres. En outre, il faudrait éviter l'exploitation et la
circulation intense dans l'érablière pendant le dégel printanier. Les tracteurs et débusqueuses
pourraient abîmer les fûts et formeront des ornières qui risquent d'endommager les systèmes
radiculaires et d'exposer les arbres à un stress accru. Les fûts et systèmes radiculaires blessés
pourraient laisser le champ libre aux champignons de la carie. Les blessures de ce genre sont plus
dangereuses que celles qu'a causées la tempête de verglas car elles sont en contact avec le sol et posent
ainsi un risque accru d'infection.
8.
Pour le rétablissement des érablières touchées par la tempête de verglas, tenez compte de la
gravité des dommages, de l'âge et de la vigueur des arbres, de la qualité du site et d'autres facteurs
importants touchant le peuplement et le site.
9.
Les résidus d'exploitation qui ne sont pas de qualité marchande et qui ne nuisent pas à l'accès
au site devraient être laissés sur place. Les résidus de plus de 10 cm (4 po) de diamètre devraient être
ébranchés jusqu'à 60 cm (24 po) du sol. Ces résidus se décomposeront avec le temps et contribueront à
la productivité du site.
10.
À l'automne 1998 seront publiées des lignes directrices révisées tenant compte de la façon dont
les arbres ont réagi pendant le printemps et l'été à la perte d'une partie de leur couronne.
11.
Si vous voulez faire de l'élagage, assurez-vous d'employer des techniques appropriées. Celles-ci
sont décrites dans le document du Landowner Resource Centre intitulé Caring for Ice Damaged Trees.
Évaluation des dommages causés par la tempête de verglas
Le système d'évaluation suivant se divise en deux sections. La section I est une méthode d'évaluation
qui vise à déterminer les arbres à entailler et le nombre d'entailles à faire. La section II décrit une
méthode d'évaluation globale des dommages qu'a subis votre érablière, qui permet d'estimer le nombre
d'entailles à faire en se fondant sur la gravité des dommages et l'application des recommandations
concernant l'entaillage des érables endommagés par la glace.
Section I : Évaluer les arbres
Lorsque vous évaluez un arbre, essayez de déterminer de quoi avait l'air la couronne avant la tempête et
quelle proportion de la couronne demeure intacte. Il est préférable d'évaluer en fonction de la
couronne qui reste, car on tend à surestimer les dommages lorsqu'on se concentre sur la partie de la
couronne qui a été détruite.
On calcule ensuite les dommages à la couronne en soustrayant ce chiffre de 100. Par exemple, si un
érable à sucre conserve 60 % de sa couronne, c'est qu'il présente des dommages de 40 %, c'est-à-dire
des dommages modérés.
Il est recommandé que deux personnes évaluent chaque arbre; en faisant la moyenne des deux
opinions, l'estimation sera plus fiable.
Catégories des dommages à la couronne
Légers
0-11 %
Modérés
11-50 %
Graves
50-75 %
Très graves
>75 %
Après avoir déterminé la catégorie des dommages à la couronne, suivez la ligne directrice sur l'entaillage
des arbres endommagés au tableau 1 (page 10).
Section II : Déterminer le nombre d'entailles à faire dans un peuplement endommagé
Les objectifs de cette évaluation sont les suivants :
1.
Déterminer de façon globale les dommages qu'ont subis les arbres de l'érablière.
2.
Estimer le nombre d'entailles à pratiquer en fonction de la gravité des dommages et de
l'application des lignes directrices concernant l'entaillage des érables à sucre endommagés par le
verglas.
Évaluation visant à déterminer les dommages causés à l'érablière et l'entaillage possible pour 1998 :
Étape 1. Préparer une carte des compartiments
Si vous disposez d'une carte des compartiments forestiers, utilisez-la pour y indiquer les dommages.
Sinon, tracez une carte simple divisée en secteurs en fonction des essences, de la composition, de l'âge,
de la surface occupée et de la structure de peuplement. Si l'érablière est relativement uniforme, elle
peut constituer un seul compartiment.
Étape 2. Évaluer un échantillon d'arbres dans trois parcelles de chaque compartiment
Pour obtenir une estimation plus fiable, répétez l'évaluation d'un échantillon d'arbres dans trois
parcelles du compartiment.
Étape 3. Évaluer un échantillon d'arbres (une parcelle)
Choisissez l'endroit où vous entreprendrez votre évaluation. N'allez pas trop près d'une route ou du
bord du peuplement, car ces zones seront plus endommagées et votre évaluation de l'érablière sera
faussée.
Essayez de choisir un endroit qui est représentatif de l'état général du compartiment que vous évaluez.
Choisissez ensuite l'érable le plus proche dont le diamètre à hauteur de poitrine est supérieur à 25 cm
(10 po). Établissez les dommages à la couronne selon les catégories indiquées à la section sur
l'évaluation des arbres. Prenez ensuite l'érable le plus proche, et continuez jusqu'à ce que vous ayez
évalué dix arbres. Répétez dans deux autres parcelles, de façon à échantillonner trois parcelles du
compartiment (voir le tableau 2, page 12).
Étape 4. Préparer un sommaire pour l'ensemble de l'érablière
Si vous avez plusieurs compartiments, la prochaine étape consiste à faire la somme des entailles
normales et des entailles rajustées pour tous les compartiments.
Entailles normales
Compartiment n° 1
Entailles rajustées
52
34
48
30
(voir l'exemple, p. 11)
Compartiment n° 2
(pas d'exemple)
100
64
Étape 5. Calculer le pourcentage des entailles qui subsistent
64/100 * 100 = 64 %. Si l'on se fonde sur le niveau de dommages dans l'érablière fictive ci-dessus et sur
les recommandations concernant l'entaillage des arbres endommagés par le verglas, il reste pour
l'érablière 64 % des entailles qu'il y avait avant la tempête.
Étape 6. Calculer le nombre d'entailles dans l'érablière
Pourcentage d'entailles dans l'érablière endommagée * nombre d'entailles dans l'érablière avant la
tempête = nombre d'entailles dans l'érablière endommagée par la tempête
Par conséquent, si vous aviez 3 000 entailles dans votre érablière avant la tempête :
0,64 * 3 000 = 1 920 entailles
Cette évaluation révèle que vous aurez 1 920 entailles, compte tenu de la gravité des dommages et de
l'application des recommandations concernant l'entaillage des érables à sucre endommagés par le
verglas.
Évaluation complète
Les résultats de l'évaluation rapide permettront de déterminer s'il faudra effectuer une évaluation plus
détaillée à une date ultérieure. Vous aurez besoin de renseignements supplémentaires pour planifier
les activités futures de gestion de votre érablière, p. ex., les dommages causés aux perches et aux gaules
ainsi qu'aux autres essences de votre boisé.
Avant d'abattre des arbres, évaluez les effets des dommages à la prochaine saison de croissance, sauf
pour ce qui est des arbres dangereux.
Des lignes directrices pour la tenue d'une évaluation complète seront publiées sous peu.
Tableau 1. Recommandations concernant l'entaillage des érablières endommagées par la tempête en
1998
Les recommandations concernant l'entaillage des érables au printemps 1998 reposent surtout sur la
proportion de la couronne qui a été perdue et la probabilité de survie de l'arbre.
Proportion perdue
Dommages
Recommandations
Justification
de la couronne
0-10 % légers Entailler comme d'habitude
Un entaillage normal est recommandé, dans la
en suivant les lignes directrices mesure où les dommages sont minimes et peu
générales ou traditionnelles
susceptibles de menacer la survie des arbres.
(Voir la ligne directrice n° 1
Le taux de survie des arbres devrait être élevé.
plus loin.)
11-50 %
recommandé pour
modérés
Entailler en suivant les lignes
directrices sur l'entaillage
Un entaillage prudent est
éviter de stresser les arbres encore plus.
prudent pour les arbres stressés
Les arbres devraient survivre, sous
réserve de la
(Voir la ligne directrice n° 2
plus loin.)
50-75 %
nature des dommages, des conditions de
croissance, etc.
graves Entaillage non recommandé
Ces arbres devraient survivre, mais
certains
seront menacés. Toute leur énergie devrait
être consacrée à survivre, à contenir les
dommages et cicatriser les blessures.
Plus de 75 %
une perte très
très graves
Entaillage non recommandé
La survie des arbres présentant
sauf pour les arbres qui seront grave de leur couronne repose sur des facteurs
abattus en 1998
tels que leur âge, le site, les conditions de
croissance et la présence de conditions
biologiques ou environnementales défavorables
au cours des prochaines années. Si une forte
proportion des arbres de votre érablière entre
dans cette catégorie, envisagez sérieusement
de ne pas entailler votre érablière en 1998.
Ligne directrice n° 1 : entaillage général ou traditionnel
Diamètre de l'arbre sur écorce, Nbre d'entailles par arbre
à 4 pi 2 du sol
moins de 10 po 0
10 à 14 po
1
15 à 19 po
2
20 à 24 po
3
25 po ou plus
4
Ligne directrice n° 2 : entaillage prudent pour les arbres stressés
Diamètre de l'arbre sur écorce, Nbre d'entailles
à 4 pi 2 du sol
moins de 12 po 0
12 à 18 po
1
18 po ou plus
2
Tableau 2. Fiche d'évaluation des arbres
Compartiment n° 1
Pour chaque arbre évalué, consignez les renseignements suivants :
DHP (po)
Nbre
d'entailles
Dommages à la Nbre d'entailles
couronne
rajusté
Parcelle n° 1
1
16
2
modérés
1
2
16
2
modérés
1
3
18
1
modérés
0
4
18
1
légers 1
5
8
0
légers 0
6
18
1
légers 1
7
24
3
modérés
2
8
24
3
modérés
2
9
8
0
-
10
24
3
modérés
1
16
1
légers 1
2
24
3
modérés
2
3
22
3
modérés
2
4
16
1
légers 1
5
16
1
légers 1
6
16
2
modérés
1
7
24
3
modérés
2
8
22
2
légers 2
9
16
2
modérés
1
10
16
2
modérés
1
1
18
1
légers 1
2
24
3
modérés
2
3
24
3
modérés
2
4
8
0
-
5
24
3
modérés
2
6
16
2
modérés
1
7
16
2
modérés
1
0
2
Parcelle n° 2
Parcelle n° 3
0
8
18
1
modérés
9
18
1
légers 1
10
8
0
légers 0
52
Nbre total d'entailles
Nbre total
d'entailles
0
34
rajusté
Bibliographie
1.
Caring for Ice Damaged Trees, Landowner Resource Centre, Manotick (Ontario), 1998.
2.
Houston, D.R.; Allen, D.C.; Lachance, D. Sugarbush Management: A Guide to Maintaining Tree
Health, North Eastern Forest Experiment Station, General Technical Report NE-129, 1990.
3.
Coons, C.F. Guide d'aménagement des érablières à l'intention des acériculteurs, ministère des
Richesses naturelles, 1992.
4.
North American Maple Syrup Producers Manual, 1996. Produit par l'Ohio State University
Extension en collaboration avec le North American Maple Syrup Council, 1996.
A Residential Tree Survival Guide - help for your damaged trees
Extension
Operation Re-Leaf (Tree Canada Foundation, Shell Environmental Fund)
1998
REF# 383
Également disponible en français sous le titre "Guide au secours des arbres - de l'aide pour vos arbres
endomagés".
The 5-day ice storm of January 1998 struck with devastating intensity and caused widespread damage to
trees.
Operation Re-Leaf was initiated by Tree Canada Foundation with the intent to assist communities
affected by the Great Ice Storm by providing information on how to save damaged trees and replace
those that are beyond repair. This Residential Tree Survival Guide is designed to assist individuals whose
own trees may have been affected.
What happened to your trees?
As the freezing rain built up layers of ice on the branches, the weight became much greater than the
trunk or branches could stand, causing them to bend or break. Trees with upward spreading branches
were most at risk since the weight literally ripped them off the trunk. Trees whose branches sloped
downwards were more resistant, but many of them bent over becoming deformed or broken.
Trees with some broken branches may be saved with a little help. As a general rule, if the tree still has
half of its branches or more, it should be possible to save it. If the damage is greater, get advice from a
professional - it still may be possible, but the chances are less.
Safety First!
Broken and weakened branches are a threat. Approach trees with caution to carefully size-up the
damage. Stay away in windy conditions. Never go near or touch a tree near a power line. Always wear a
hard hat and gloves, and have a partner to watch out for you as you work.
It is important to have damaged branches removed for personal and public safety as well as for the
health of the tree.
Caring for your damaged trees
Trees heal themselves by growing over damaged areas. The idea in pruning is to make smooth clean
surfaces so the healing can proceed smoothly. Smooth cuts resist decay and insects better than ragged
breaks. Proper tree care can also promote more rapid growth and vigour to resist the stresses of winter
drying and frost.
Pruning
•
All damaged branches should be pruned (sawed or cut off) to prevent further damage and to
promote healing.
•
Pruning should be done as soon as possible.
•
Prune branches at the base - but do not cut them off flush with the bark on the trunk. Leave the
'branch collar'- the raised ring of bark around the base - this has protective tissue that helps healing.
(Figure 1) The projecting stubs will soon be covered over as the tree grows around them.
•
Cut the branch with a slightly sloped angle so water will run off. This helps to stop rot. (Figure 2)
•
Larger branches tend to rip off bark from the trunk as they fall - cut them in a 3-step approach:
(Figure 3)
Call a professional pruner for big or complex jobs, especially if:
•
The tree is close to a power line.
•
Climbing is necessary to reach branches.
•
Trees are large and a power saw is required.
Repairing torn bark
•
Use a sharp knife or chisel to smooth ragged edges, and remove any loose bark.
Wound dressings
Do not use wound dressings or paints. The wounds will heal on their own if the cuts are clean and water
is able to run off.
Tree care
Give extra care to your trees as they recover from their stress. Water them during dry periods. Proper
watering means saturating the soil under the tree as far out as the ends of the branches. Most arborists
suggest not fertilizing damaged trees this year.
Watch for signs of distress - drooping, wilting, pale leaves, especially die-back from the branch tips. Do
more pruning of branches that are dying. Ask for advice if there are signs of insects or diseases - they
may not be harmful. For example, sun scald is a condition that develops when bark is suddenly exposed
to full sunlight. The bark may become discoloured, but there is no required treatment. There may be
problems with tree-feeding insects during the summers of 1998 and 1999 since the presence of so many
weakened trees may encourage build-up of populations.
Tree replacement
We encourage you to replace trees that have had to be removed. They add so much to our living
environment. Ask about suitable species at tree nurseries or with municipal arborists. Choose ones that
are hardy for the region, suitable for the soil, and with branching habits that are less susceptible to ice
storm damage.
Plant trees at least 3 metres from building foundations and keep them away from overhead wires or
underground utility lines.
Need advice?
Additional information and advice may be obtained from your municipal arborists, horticulturists, or
local tree nurseries.
This brochure has been developed in partnership with Shell Canada Limited and the Tree Canada
Foundation.
Since it was created in 1990, the Shell Environmental Fund has funded grassroots environmental
projects across Canada. To date, more than 2,000 projects have benefited from its assistance. Thanks to
this resource - up to $5,000 per project - community and environmental groups have restored habitat,
cleaned up beaches and roads and built trails. Other projects are aimed at conservation, waste
reduction, recycling, and environmental education. All of these activities are designed to assist
communities to find solutions to today’s environmental issues. The Shell Environmental Fund has
invested more than five million dollars into these projects to date, to improve and preserve the
environment from coast to coast.
The Shell Environmental Fund asks regional panels of environmentalists and government
representatives to assist Shell to make the grants. There are separate panels for Quebec, Ontario and
Atlantic Canada.
For more information, visit the Shell Canada web site at http://www.shell.ca, or contact.
Ontario and Atlantic
Sheila Butler, Shell Canada Limited
P.O. Box 100, Station M , Calgary, Alberta , T2P 2H5
Tel: (403) 691-2071
Quebec
Nicole Belval, Shell Canada Limited
7101 rue Jean-Talon Est , Bureau 900
Anjou, Quebec H1M 3S4
Tel: (514) 356-7036
The Tree Canada Foundation is a not-for-profit, charitable organization that creates public awareness
and educational programs to inform Canadians of the role trees play in improving our communities.
Established in 1992, the Foundation provides education, technical assistance, resources and financial
support through working partnerships to encourage Canadians to plant and care for trees in our urban
and rural environment.
For more information, visit the Tree Canada Foundation web site at http://www.treecanada.ca, or write
to:
Tree Canada Foundation, 220 Laurier Avenue West, Suite 1550, Ottawa, ON, K1P 5Z9, Tel: (613) 5675545, Fax: (613) 567-5270, E-mail. [email protected]
Guide au Secours des Arbres - de l’aide pour vos arbres endommagés
Extension
Opération Renouvert (Reboisons le Canada, Le Fonds de l’environnement de Shell)
1998
REF# 384
Also available in English, entitled "A Residential Tree Survival Guide - help for youir damaged trees".
La tempête de verglas d'une durée de cinq jours du mois de janvier 1998 a été dévastatrice et a causé
beaucoup de dommages aux arbres.
Opération Renouvert a été lancée par la Fondation canadienne de l'arbre dans le but de venir en aide
aux municipalités affectées par la tempête de verglas et de prendre des mesures afin de sauver les
arbres endommagés et de planter de nouveaux arbres pour remplacer ceux qui sont vraisemblablement
perdus. Le présent guide a été conçu afin de venir en aide aux citoyens dont les arbres peuvent avoir été
endommagés.
Qu'est-il arrivé à vos arbres?
L'épaisse couche de verglas qui s'est accumulée sur les branches est devenue plus lourde que ce que le
tronc ou les branches ne pouvaient supporter, de sorte que les arbres ont plié et même cassé. Les arbres
dont les branches s'étalent en hauteur ont été les plus vulnérables car le poids de la glace a
littéralement arraché les branches du tronc. Les arbres dont les branches se recourbent vers le bas ont
mieux résisté. Par contre, plusieurs de ces arbres se sont repliés sur eux-mêmes et se sont déformés ou
brisés.
Les arbres qui n'ont subi que quelques cassures au niveau des branches peuvent être sauvés si on vient
à leur rescousse. Règle générale, les arbres qui ont conservé la moitié de leurs branches ou plus
pourront sans doute être sauvés. Si les dégâts sont plus importants, renseignez-vous auprès de
professionnels. Certains survivront mais leurs chances sont moins bonnes.
La sécurité avant tout
Les branches affaiblies et brisées sont dangereuses. Approchez-vous prudemment de l'arbre afin
d'évaluer l'ampleur des dégâts. Ne vous approchez pas des arbres par grands vents. N'approchez pas et
ne touchez pas aux arbres situés près des lignes de haute tension. Portez toujours un casque de sécurité
et des gants. Obtenez l'aide de quelqu'un pour vous surveiller pendant que vous travaillez.
Les branches endommagées doivent être enlevées pour la sécurité du public et la santé de l'arbre.
Les soins à apporter aux arbres endommagés
Les arbres se guérissent eux-mêmes en créant de nouvelles pousses sur les sections endommagées.
Tailler un arbre a pour but de créer une surface lisse et propre qui accélérera la guérison. Les coupes
lisses résistent mieux à la pourriture et aux insectes que les bris déchiquetés. De plus, des arbres bien
soignés croîtront mieux et seront plus vigoureux, de sorte qu'ils résisteront mieux aux rigueurs de l'hiver
et au gel.
La taille
•
Taillez (coupez ou sciez) les branches endommagées afin de prévenir de plus graves dommages
et d'accélérer la guérison. Faites la taille aussitôt que possible.
•
Taillez les branches à la base. Ne les coupez pas à la hauteur de l'écorce du tronc. Laissez le
«collier de la branche» (l’anneau surélevé à la base de la branche) car il contient des tissus protecteurs
qui contribuent à la guérison. (Figure 1). Ce moignon sera vite couvert par les autres branches de l'arbre.
•
Coupez la branche à un angle un peu incliné afin que l'eau puisse s'écouter et arrêter la
pourriture. (Figure 2)
•
Les grosses branches arrachent l'écorce du tronc en tombant. Taillez-les en suivant ces trois
étapes: (Figure 3)
Si vous devez couper de grosses branches ou que la taille professionnel, surtout dans les conditions
suivantes:
•
L'arbre est situé à proximité de lignes de haute tension.
•
Vous devez grimper dans l'arbre pour atteindre les branches.
•
Les arbres sont gros et vous devez utiliser une scie à chaîne.
La réparation de l'écorce déchirée
•
Utilisez un couteau coupant ou un ciseau à bois pour lisser la surface et enlever l'écorce qui s'est
détachée.
Le traitement des plaies
N'utilisez pas de goudron végétal ni de peinture. Les plaies guériront d'elles-mêmes si les tailles sont
franches et que l'eau peut s'en écouler.
L'entretien des arbres
Prodiguez plus de soins à vos arbres pendant leur période de récupération. Arrosez-les en cas de
sécheresse en saturant le sol sous l'arbre, sous toute l'envergure des branches. La plupart des arboristes
suggèrent de ne pas fertiliser les arbres endommagés cette année. Surveillez les signes de détresse,
comme des feuilles tombantes, fanées et pâles, surtout le dessèchement des extrémités des branches.
Taillez les branches qui meurent. Renseignez-vous si vous remarquez la présence d'insectes ou de
maladies. Ces facteurs ne sont pas tous nuisibles. À titre d'exemple, l'ercissement est un état qui
survient lorsque l'écorce est soudainement exposée à la lumière directe. L'écorce peut se décolorer et il
n'existe aucun traitement pour cet état. Les insectes mangeurs d'arbres pourraient poser un problème
pendant les étés 1998 et 1999 car l'affaiblissement des arbres peut encourager la formation de
peuplements.
Le remplacement des arbres
Nous vous encourageons à remplacer les arbres qui ont été enlevés. Comme vous le savez, les arbres
sont un atout pour l'environnement. Discutez des espèces à choisir avec l'arboriste de la pépinière ou de
la municipalité. Choisissez des arbres robustes qui conviennent à la région et au sol, et dont le mode de
croissance des branches est moins vulnérable aux dommages causés par les intempéries.
Plantez vos arbres à au moins trois mètres des fondations et éloignez-les des fils aériens et des
conduites souterraines.
Vous voulez des conseils?
Pour obtenir de plus amples renseignements ainsi que des conseils pertinents, adressez-vous à votre
arboriste municipal, à votre horticulteur ou aux pépinières locales.
Ce dépliant est le fruit d'un partenariat entre Shell Canada Limitée et la Fondation canadienne de
l'arbre.
Depuis sa création, en 1990, le Fonds de l'environnement de Shell ne cesse d'appuyer la réalisation de
projets innovateurs partout au pays. Jusqu'à présent, plus de 2 000 projets ont bénéficié de son soutien.
Grâce à des montants pouvant s'élever jusqu'à 5 000 $, des collectivités et des groupes
environnementaux ont mené à bien des projets de remise en état d'habitats, de nettoyage de plages et
de routes ou d'aménagement de sentiers. D'autres projets visaient la réduction des déchets, le recyclage
et la sensibilisation à l'environnement. Tous ces gestes, posés au profit des collectivités, représentent
autant de solutions aux problèmes environnementaux d'aujourd'hui. À ce jour, le Fonds de
l'environnement de Shell a investi plus de cinq millions de dollars dans ces projets en vue d'améliorer et
de préserver l'environnement d'un bout à l'autre du pays.
Pour l'approbation des projets, le Fonds de l'environnement de Shell fait appel à des comités régionaux
formés d'environnementalistes et de représentants du gouvernement. Des comités distincts sont formés
pour le Québec, l'Ontario et l'Atlantique.
Pour de plus amples renseignements, consultez le site Web de Shell Canada, http://www.shell.ca, ou
communiquez avec:
Québec
Nicole Belval, Shell Canada Limitée
7101, rue Jean-Talon Est, Bureau 900
Anjou (Québec) H1M 3S4
Tél. : (514) 356-7036
Ontario et Atlantique
Sheila Butler, Shell Canada Limitée
PO. Box 100, Station M, Calgary (Alberta), T2P 2H5
Tél. : (403) 691-2071
La Fondation canadienne de l'arbre est un organisme de bienfaisance à but non lucratif dont le rôle est
de sensibiliser le public et de créer des programmes éducatifs afin d'informer la population canadienne
du rôle que jouent les arbres dans l'amélioration de nos collectivités. Créée en 1992, la Fondation offre
des programmes d'éducation, une assistance technique, des ressources et un appui financier au moyen
de partenariats de travail visant à encourager les Canadiens et les Canadiennes à planter des arbres dans
nos forêts urbaines et rurales et à en prendre soin.
Pour plus de renseignements, visitez le site Web de la Fondation canadienne de l'arbre à
http://www.treecanada.ca, ou écrivez à: La Fondation canadienne de l'arbre, 220, avenue Laurier Ouest,
bureau 1550, Ottawa (Ontario) K1P 5Z9, téléphone: (613) 567-5545, (613) 567-5270, courriel:
[email protected]
Ice Storm of ‘98: Harvesting Hazards
Extension
American Pulpwood Association Inc.
Stewart Hall, Certified Logging Professional, P.O. Box 557, Jackman, Maine 04945
1998
REF# 386
Introduction
Recent ice storms in the Northeast have left large tracts of forestland ravaged by the effects of heavy ice
build-up on tree limbs. As one old timer lamented, “it looks as though Mother Nature shucked all the
limbs off the oak to pick her teeth with’em.” The costs to landowners are steadily rising as people begin
to survey the damage. Loggers who harvest and salvage in these areas must assess these storms’ effect
on harvesting safety and productivity.
Although hardwood species were generally hardest hit, many softwoods were also luckless recipients of
up to six inches of ice build up on their limbs in the worst areas. Hazards have been created overhead
and at ground level. Each type of hazard should be addressed and assessed accordingly.
Managing Hazards
Identify the hazard
The dangers created by the ice storms are, for the most part, everyday logging hazards; what’s unique
about them is their large number. Overhead hazards should be identified first. The most common
overhead hazards will be broken limbs, widowmakers, and uprooted trees or partially uprooted tress
that lean into other trees. Second, examine ground level hazards, spring poles and bent over trees
demand the utmost respect. In addition, the snow cover in February and March will likely cover some
ground level hazards. The ground is littered with broken limbs and downed trees, making it hard to
deduce what is under tension and what is not.
Figure 1. Ice storm damage causes various overhead hazards, as well as spring poles.
Evaluate the hazard
Ask yourself, “Can I work near this hazard without jeopardizing my safety?” If the answer is “no,” or
even a borderline “maybe,” then the loggers must next consider why this is a hazard and what are the
options for managing it. Loggers must know the limitations of their equipment and experience. Having
mechanized equipment on hand is a sure-fire way of eliminating exposure to broken limbs and even
spring poles, but a logger who is cleaning up debris around houses or in an area where machinery is not
an option must rely on his judgment and ability.
Manage the hazard
Either eliminate the hazard itself or the exposure to it.
•
Eliminate the hazard. It’s important that loggers understand that no techniques can be counted
on 100% of the time. In the aftermath of this storm, concerns arise as even the best techniques are
ineffective.
•
Avoid the hazard. Stay a minimum of two tree lengths away.
Recommendations:
•
Remember-if the hazard cannot be eliminated, avoid exposure to it.
•
Overhead hazards can be most easily dealt with from a protective cab.
•
For chain saw/skidder crews, several techniques may be effective. First, knowing that the worst
place for a feller to be standing as an ice-laden tree is falling is near its base, plan and use good escape
routes.
•
Conditions may warrant that the logger not be anywhere near the tree once it starts to movefor example, when overhead limbs may be dislodged as the tree descends through the canopy. In these
situations, the skidder can push both forward-leaning trees and back-leaning trees. Pushing over backleaning trees makes sense, but how does someone push over a tree that’s already headed where they
want it to go? This is where the use of a bore cut and back-strap come in handy. The feller first properly
notches the tree. He then bore cuts to establish a hinge, then leaves a back-strap on a forward-leaner.
The logger can now return to his protective cab and use the skidder to push over the tree by breaking
off the strap.
•
Back-leaning trees that would normally be brought over using a wedge can be dangerous to
stand under and hammer on because the pounding can dislodge ice and limbs. Instead, insert a wedge
to hold the tree from setting back, and push the tree over with a skidder.
•
Spring poles and bent-over trees are dangerous because the wood fiber is under tension. Many
tree tops are bent over and frozen into the ground. The best option is to use machinery to eliminate the
tension. For the chain saw operator, first release the top by cutting and freeing the limbs frozen into the
snow. This action will lessen some tension on the butt-end of the tree. After this release, and each
additional felling cut, delay further action on that tree to allow time for the fibers to weaken, and more
tension to be released. (However, do not turn your back on, or leave, a partially cut tree!)
•
Large bent-over trees are a particular hazard because traditional notching and backcutting
techniques may barber-chair, regardless of how careful the chain saw operator is. Follow the rule: if the
hazard cannot be eliminated, avoid the hazard.
Figure 2. Even though standing to one side and cautiously cutting at waist level reduces exposure…
Figure 3. …tension release can still be dangerous!
Landowners Beware: Please avoid this dangerous practice!
Outlook
Beyond the remaining winter months, consider the following:
•
What will happen when the foliage fills in this spring and conceals overhead hazards?
•
What effect will wind have on these hazards?
•
How long can we expect debris to be raining down?
•
Trees that have been bent over for a long period of time will have much of the tension wrung
out of them, but still should not be trusted. Will spring-poles continue to pack a wallop or will they
simply barber-chair more easily?
•
How has the ice affected existing hazards such as stubs and dead or dying wood?
APA Staff Comment
•
Landowners may wish to consider using a simple repeatable method to measure the amount of
damage the ice storm has caused to their woodlot. Measuring Residual Damage (APA 97-R-58) outlines
such a method.
•
Landowners should also act knowledgeably when contracting with loggers to salvage ice
damaged woodlots. (Contact your State Forestry Department for advice, or obtain APA’s “How to Select
a Quality Logger” pamphlet.)
•
Loggers should re-read Managing Dead Trees and Stubs (APA 92-R-11) for an OSHA approved
guide to working around these hazards.
•
Using a skidder to push over trees is not the normal operating procedure. Regular use of
skidders to fell trees indicates poor understanding of proper felling, and in the long run, is economically
unsustainable.
Reviewed by: Tim Gammell, Northeastern Technical Division Forester
The Ice Storm - Its Aftermath
Extension
Maple Syrup Digest
Lucien Blais
Vol. 10A, No. 2
June 1998
REF# 402
We have seen the pictures and heard the statistics on the Ice Storm of 1998. With millions of taps lost
we wondered about the future of maple and some made dire predictions of a shortage of syrup. Now it
appears that the overall crop may be close to average and, fortunately, the industry will survive and
remain healthy. But, for thousands of producers from areas of maple country hit by the ice storm, life
will not be the same. For many the future is uncertain and some, I understand, have already decided
that there is nothing to salvage.
I know we will never forget these three days and two nights in January when the freezing rains came
and we heard and watched our sugarbush and woodlot being dismantled limb by limb. The leaves are
starting to come out now but as we look up at our mangled trees it seems we can still hear the echoing
of the constant snapping and crashing of limbs and tree tops. Fortunately, no one was hurt and our
home was not damaged.
The decision not to tap this year did not come easy. This spring tradition has become so ingrained in our
family and community after 77 years of tapping our trees and boiling sap. With most of our tubing down
and encased in ice, it was financially unrealistic to try to dig up our 4000 taps. Most painful to us was
going out in the morning, stepping on crunchy snow, feeling the warmth of the sun and not having a
tank to run to to check the sap flow. Fortunately we were able to buy some syrup to make our
traditional products and service our customers.
We have started the long clean up process of cutting downed limbs and salvaging the wood. Our eyes
often look upwards wondering how many trees will actually survive or at least produce enough sap to
make it worth our while. With only a fraction of the work done our sugarwood pile is already beyond a
two year supply, especially when considering the anticipated reduction in production.
We will be putting our tubing back up and tapping our two bushes again next year. There's just too
much invested in time, equipment and tradition to just call it quits. We feel we need to find out first
hand what the effects of this storm will be on our trees. The foresters are helpful and at times
encouraging, but with so many unknowns it's obvious that only time will tell.
This is only one producer's story, but I'm sure it can be recounted many times over in parts of Maine,
New Hampshire, Vermont, New York, Quebec and Ontario. It's meant to simply go beyond the statistics
and present the human perspective. (photos)
Estimated Loss of 1998 Maple Syrup Production Resulting From Ice Storm in Northern New York
Extension
Maple Syrup Digest
Lewis Staats, Extension Associate, Cornell University Maple Program
Vol. 10, No. 1
June 1998
REF# 403
An ice storm occurring during the period of January 7-10, 1998 in northern New York resulted in major
power outages and telephone service interruptions ranging from a few days to weeks. In some of the
areas effected, over 5 inches of rain was experienced over an extended period. Rain fell and froze on the
cold ground, power lines, and trees. The result of this unusual weather event created hardships across
northern New York, New England, Eastern Ontario, and southern Quebec.
Counties where the most severe ice damage occurred were placed under a federal state of emergency.
The counties of Clinton, Essex, Franklin, Jefferson, St. Lawrence and Lewis were declared as federal
disaster areas. The primary damage in Lewis County resulted from flooding in the southern portion of
the county although some ice damage occurred in northern areas of the county. The ice storm damage
to northern hardwood forest stands including sugar bushes in the northern region ranged from little or
no damage to severe. The most extreme damage seemed to follow waterways and was most prevalent
at elevations below 2,000 feet. At elevations above 2,000 feet, slopes with a northeastern exposure
received damage also.
Northern New York is a major maple syrup producing region of the state. According to New York
Agricultural Statistics reports, about 25 percent of New York's producers reside in the 6 county region
and produce about 35 percent of the state's maple syrup. The immediate concern is the ice damage
preventing access to and within sugar bushes for setting up sap collection systems and tapping for the
fast approaching production season. Downed tops and branches must be removed or lopped in order to
allow work in the effected sugar bushes. Many maple producers had plastic tubing sap collection
systems in place in their sugar bushes at the time of the storm. The tubing and pipeline systems, now
buried under branch debris and tree tops, will require substantial repair or replacement before the
systems can function. The following estimate of loss of crop (percentage or taps producers will not put
into production due to restriction of access or tree damage and/or loss) for 998 is based on flights over
the northern counties, reports from maple producers, information forwarded from Cornell Cooperative
Extension (CCE) agents, and a limited number of on-site evaluations.
The figures on the next page are based on crop reports from the NY Agricultural Statistics Service. The
percent of estimated loss is based on the information available at this time and projects as estimated
loss for the 1998 maple season. More time and investigation will be required to determine the recovery
of maple production in the 6 northern New York counties beyond 1998. With snow cover over the
branch debris and access into sugar bushes difficult and dangerous at the present time, the estimated
loss is subject to change as more information from the region becomes available. Additional financial
impact associated with the 1998 production season and beyond is the loss associated with sales of
maple equipment and supplies, and seasonal labor opportunities so important to rural economies of
northern New York.
County Producers
# Taps # Acres % Estimated Loss for 1998
Clinton 52
180,000
3,600 approaching100%
Essex
34,000 685
40%
45
Franklin
26
30,000 600
60%
Jefferson
28
34,000 480
50%
Lewis
261,000
120
St. Lawrence
120
5,220 20%
142,000
2,840 80%
Of much greater concern and of great economic impact is the long term effect from damaged trees.
Sugar maples with broken trunks without crowns and those that are uprooted will be lost to production.
The loss of these trees will leave a void in sap production over a long period of time (approximately 40
years are required for a maple to reach tapping diameter). There is no accurate estimate this early after
the storm, but many producers are reporting 30 to 50 percent of their trees are lost while others feel
they have loss nearly all their trees. The process of restoration of damaged stands of sugar maple to
desired levels of productivity will require individual producer decision making and great effort for years
well into the future.
It is apparent that many producers will not be able to tap this year because excessive branch debris will
restrict access, and sap collection systems have been damaged and are under layers of ice and snow.
Additionally, the process of clean-up under these conditions will be very difficult. If clearing of access
roads or sap collections systems are initiated, safety precautions should be practiced at all times. Maple
producers are encouraged to resist making hasty management decisions. To help in the decision making
process of how best to manage damaged sugar bushes, producers should seek advice from a forester.
Information regarding the services of DEC foresters and consulting foresters is available at DEC and CCE
offices.
Literature Search on Key Words - Ice Storm, Glaze and Crown Damage
Extension
REF# 389
Health of sugar Maple in Canada - Results of the North American Maple Project 1988-1993
Lachance, D. et al. 1995. Published by the Canadian Forest Service
Prognosis based on level of dieback in crown on sugar maple
Change in crown dieback over 5 years by dieback class:
0-15% - most trees in this class remained within this class
(2.2 % died- normal rate of mortality)
16-35%
- 69% improved to 15% or less
- 10% died (2% per year - still normal)
36-55%
- 43% improved to healthy
- 31% died
>55%
- likely die within 5 years (75% died)
(Applicability of the results are somewhat limited because dieback reflects overall decline rather than
sudden loss of crown on otherwise healthy trees).
Forest Ecology of Ice Storms
Lemon, Paul C. 1961. Bulletin of the Torry Botanical Club, Vol. 88, No. 1, pp. 21-29
Dates of glaze storms in NY state- 1884, 1909, 1914, 1922-23, 1925, 1929-30, 1936, 1942-43, 1948-49,
1956-57, 1959. (note date of article)
-
glaze is recurring feature in natural environment
-
glaze of one fourth to one inch causes breakage of small branches
-
one half to one inch young trees broken across bole
-
elms dies due to entry sites for insects
-
damage susceptibility chart
Very
Moderate
Resistant
elm
sugar maple
white ash
basswood
beech shagbark hickory
butternut
white pine
red spruce
cottonwood
hemlock
yellow birch
silver maple
gray birch
black cherry
quaking aspen
red oak
Species showing permanent set (fail to recover from bending)- gray birch, red cedar, cherry and
willow
-
processes which result in unbalanced crowns (i.e. edge trees) increase susceptibility
higher susceptibility of birch elms and several species of poplar as compared to maple and
beech, hemlock accelerates succession.
-
gray birch arches and does not fully recover
-
more closely spaced trees suffer less damage then open grown trees
Excessive oak mortality following ice storm damage
B. W. Dance and D.F. Lynn. 1963. Canada Dept. For. Bi- monthly Progress Report. Vol 19. Report No. 6
1959-60 ice storm north of Toronto
summer 1963 observations
-
red oak, cherry and white ash species most affected
-
good site for red oak
-
high stocking, 80 years old, 14.0 inch DBH, 90 feet tall, Oak 65% of BA
-
42% mortality in 1 acre sample
-
dieback symptoms and stag headed on remaining oaks
-
adventitious shoots on lower stems
-
50% reduction in growth after storm on severely diseased trees, continued slow
growth
-
healthier trees showed similar reduction
-
Armillaria mellea in dead and dying trees
-
ice storm had caused breakage of large branches
-
abnormally small crop of branches produced in 1960
-
speculation that weakened condition predisposed oak to A. mellea
Top rot in glaze damaged cherry and sugar maple on the Allegheny Plateau
W.A. Campbell and R.W. Davidson. Journal of Forestry
-
storm 1936
-
21.5% hardwoods damaged - 17% severely
-
wounds examined 19 months after storm
-
cherry - white decay progressed 3-24 inches in heartwood below break
-
average extent of visible decay- 14 inches
speculated that decay would continue, however observations at 40 months showed that on
average visible decay extended 23 inches from wound, extent increased with diameter of branch broken
-
30 inches for 4-5 inch branches and larger
-
decay from breaks under 5 inches in sugar maple was 6 inches or less from wound
-
practically all wounds were infected by white rot fungus
-
conclusions:
decay in cherry with less than 6 inch diameter broken branches - limited to 2-3 feet below
wound and less than 6 inches for sugar maple
good risks for saw timber production provided the breaks are restricted to branches and upper
part of main stem and are accompanied by vigorous crown regeneration
trees with badly splintered or shattered tops are poor risks for saw timber and should be utilized
within 10 to 15 years
Glaze Damage in the birch-beech-maple-hemlock type of Pennsylvania and New York
Downs, A., 1938. Journal of Forestry.
-
paper on impact in of ice storm in 1936 in relation to species, age, diameter
-
concluded increased damage with stand age
damage increased with increased size, dominant trees had more damage due to greater size and
exposure
susceptibility of species from worse to least- black cherry, sweet birch, red maple, yellow birch,
beech, sugar maple, eastern hemlock
predicts future losses in terms of decreased volume growth, due to crown destruction and
opening of stand to desiccation- decreasing site quality, decreased quality due to rot and insect attack,
and entrance of “weed” trees into stand
speculate that beech sprouts will take advantage of ice damage opening of canopy more than
maple seedlings which will compensate for more beech damage and therefore maintain beech
component, even in areas where ice storms are frequent
Relationship - crown dieback and carbo content and growth of sugar maple
Renaud, J.P. and Y. Mauffette. 1991 Can. J. For. Res. Vol. 21, pp.1111-1118
-
defoliation experiments show A. mellea is stimulated by defoliation
-
roots of defoliated trees- glucose and fructose increased 200%
Decay Following Glaze Storm Damage in Woodlands of Central New York
Spaulding and Batton, 1946, Journal of Forestry (good paper)
-
northern hardwood NY -severely damaged by ice, December, 1942
-
1945 observations showed sap rot at bases of injured but living maple
most obvious destructive effect was breaking up of crown cover and exposure of trunks and soil
to full heat and drying of the sun
-
initial wound thought to be due to sunscald caused by sudden opening of the stands
First fungi to attack - Daedalea unicolor, others found- P. hirsutus, pergamenus, tulipiferus,
versicolor, Schizophyllum commune.
Beech sprouted somewhat less vigorously, but enough new growth to prevent infection of the
main stem
sugar maple sprouted less, does not sprout sufficiently to replace lost branches to any extent,
trees with less than half there crown now alive are not likely to resume vigorous growth
-
rot likely to run downward from large broken branches within ten years
-
sap rot much worse in sugar maple than beech
-
sap rot mostly in trees with 85% crown damage and greater
-
sap rot primarily found in trees 18 inches or less
decay extending into trunk from breakage wounds in the crown are of two types; sap rot and
heart rot
Daedalea unicolor present in sprouted trees- once it enters a living tree continues until tree is
dead, therefore, trees found bearing its fruiting bodies should be salvaged as soon as possible
-
rot in beech from large branch breakage likely to progress faster
-
Abundant sprouting in tops of white ash and basswood even when stripped of all branches
-
basswood sprouted so profusely that could hardly see crown loss 2 years after damage
-
can hold trees for 10 years
white ash has greater resistance to rot - trees with large broken branches can still be held longer
than 10 years
Glaze damaged red and scots pine, Southeastern Manitoba
J. Cayford and R.A. Haig. 1961. Forestry Chronicle
1958 storm, Manitoba
-
26 year old red pine
-
12 year old scots pine
-
-
trees sampled and degree of bending recorded as:
-
less than 10 degrees
-
10-20-slight
-
21-35-moderate
-
36-90-badly
-
more than 90 (arched)
-
top broken, 1 half
-
top broken more than half
results indicated that younger plantations showed more bending but less permanent damage
16- 22 yr old red pine greatest permanent damage- stems not stiff enough to resist but too stiff
to recover
-
all trees slightly bent, moderately or badly bent and 65% of arched recovered by autumn
-
trees in 16-22 yr class had 25% of trees with permanent damage
-
trees that were still moderately, badly or arched by autumn after the storm did not recover
Glaze damage in forests in Southeastern Manitoba
Cayford, J. and R.A. Haig. 1961. Forest Research Branch Technical Note No. 102
-
same damage scale used to record stem bending and breakage as above
-
30 year old jack pine
-
trees that did not recover after one growing season were permanently damaged
-
from damage to spring- 29% arched fully recovered and 25% were only slightly bent
from spring to autumn after storm- 50% slightly bent recovered completely and 80 % of
moderately bent recovered or improved to the slightly bent class
-
if trees are still arched or badly bent after growth resumes- low chance of recovery
important to note that although mod, badly and arched trees did recover it has been shown that
compression failure can occur without breakage- so even trees that appeared to recover may contain
compression failures which will make them unfit for some future uses.
Managing pines in the ice-storm belt
H.L. Williston. 1974. Journal of Forestry
-
loblolly pine - 11 years old- top damage-loss of half of live crown
-
enough trees recovered to have viable plantation
-
slash pine, longleaf pine, recovered from bending
-
90 % recovery on slightly bent trees
-
40% and 56 % recovery on badly bent lob and longleaf resp
-
pine 12 feet and 2 inch DBH- bent beyond 40% recovered but retained degrees of crook
-
with 60% and greater -did not recover
-
periodic moderate thinning - produces stands resistant to ice damage
-
thin from below
-
recently thinned stands- more damage
How to Evaluate and Manage Storm-Damaged Forest Areas
Patrick Barry et al. 1993. Forest Service Southern Region Management Bulletin R8-MB 63 (written
specifically for southern U.S. but some useful information)
-
Steps in assessing damage include- mapping, aerial photo, ground checking
-
Priorities for salvage depend on location, amount, type of damage and management objectives.
To estimate the volume of timber to be salvaged in an area of down trees - estimate from cruise
in adjacent intact area, determine vol. per ha and apply to ha’s damaged.
-
breakage lowers timber value due to loss of specified lengths
-
also difficulty in logging in damaged stands lowers productivity
-
hardwood trees seldom killed by breakage
even when tops gone, new branches will sprout and the tree will recover. In hardwoods, major
problem is that breaks in trunk and large branches (over 3 inches) permit entry of stain and decay fungi.
-
stain moves vertically form injury- 6-18 inches per year, decay follows in 8 to 10 months
most species pine will die if tops are completely broken off, if three of more live limbs are left,
loblolly and slash pine have 75% chance of survival and will recover in 8-10 years, however, loss of
growth and crook and stem.
hardwoods, trees with broken tops and 3 inch diameter branches would be salvaged during next
scheduled harvest
-
high value trees in recreational areas and yards should be pruned
-
for pines, any tree with three or less live limbs should be harvested as quickly as possible
-
uprooted trees degrade quickly - stains, decays, bark beetles, borers, etc.
has chart of sequence of invasion of damaging organisms, in general year 1 for pine - bark
beetles, sawyers, blue stain fungi, soft rot fungi
for hardwoods, year 1 - wood borers, beetles, stains, soft rot fungi and year two, sap and
heartwood decay fungi
-
oak and hickory - same as above but year two sapwood decay fungi only
root sprung trees will not die immediately but will show signs of decline therefore pines with
major root damage should be salvaged as soon as possible
stem wounds on hardwoods from falling branches and trees, if wound does not penetrate more
than 2 inches into sapwood and is less than 144 in2- only local stain, little decay
-
wounds that exceed these limits will have stain and decay
bent trees usually not attacked by beetles due to lack of stress- unless pine is cracked and resin
flow occurs
small trees under 15 feet- straighten after bending - taller trees that bend should be removed in
salvage operation
should many large green standing trees may not be usable for veneer, poles, or lumber due to
internal ring shake, splintering, and separation of wood fibers
-
only external evidence may be pitch or resin flow
plan salvage operations to minimize insect and disease build up and attack of standing timber,
monitor after salvage operation
Snow Damage to boreal mixedwood stands in northern Alberta
Don Gill. 1974. The Forestry Chronicle
-
height of stem breakage increased with stand density
-
birch and poplar that was bent- revisted after two years- did not recover
-
trees greater than 15 cm dbh broke rather than bending
Abstract info - paper not yet received
Record 9- Glaze Storm Damage to western New York forest communities. Seischab, FK. 1993. Bulletin of
the Torrey Botanical Club
-
Western NY ice storm 1991
-
2 cm or more ice on forest.
-
30-60% crown damage on black willow, black oak, red oak
-
green ash- 11%
-
forest edges and steep slopes most damage
-
east and north facing- more damage
-
asymetrical crown had influence on increase in amount of limb breakage and tree throws
Record 6 U of T search
Absence of Decay development in tow cases of top mortality in conifers. J.T. Basham. 1971. Bi-Monthly
Research Notes, 27(3)
later
damage to young white pine and jack pine tops- no decay found when checked 15 and 7 years
How to Evaluate and Manage Storm-Damaged Forest Areas
Extension
USDA Forest Service
Patrick J. Barry, Coleman Doggett, Robert L. Anderson, Kenneth M. Swain
Management Bulletin R8-MB, 63 Supersedes Forestry Report SA-FR 20
September 1993
REF# 394
Introduction
Hurricanes, tornadoes, and ice storms strike somewhere in the South almost every year. They cause
extensive forest damage by uprooting, wounding, bending, and breaking trees. Standing water, which
often accompanies hurricanes, can cause additional stress and mortality. When one of these natural
disasters occurs, it is important to have a plan for managing damaged timber. (photos)
Development of a storm damage management plan involves several systematic steps. As soon as
possible, the area should be sketch mapped or aerial photographed. The next step is to ground check
the damage to determine the need for salvage. Priorities for salvage will depend on location, amount
and type of damage, and management objectives. This guide presents methods for managing stormdamaged trees to reduce growth loss, product degrade, and mortality. In the process, other factors such
as threatened and endangered species must be considered. The information presented here will assist in
setting priorities.
Survey the Damage
Two types of surveys, general and intensive, are needed to determine the extent of forest damage from
a storm.
General surveys are designed to determine geographical area affected by storms. These are very quickly
and easily done from the air. Using aerial survey techniques, damaged areas may be sketched on
preexisting maps or photographs, or damaged areas may be aerially photographed. A planimeter or
other device is then used to determine acres affected.
Intensive surveys are designed to collect information on volumes of timber damaged and on conditions
of surviving trees. Volumes of storm-damaged timber are difficult to estimate with aerial survey
techniques because damaged trees are broken and twisted together. It is also difficult to determine tree
condition from the air. Consequently, intensive surveys usually require ground-based plots for
acceptable accuracy. The number and size of plots are determined by desired accuracy, and by time and
personnel constraints.
Tornado damage surveys are unique because the storm tracks are usually long and narrow with few
surviving trees. Volumes of tornado damaged timber may be estimated by taking systematic plots on a
transect parallel to the storm track but just outside the damage area.
Figure 3. Hurricane-damaged stand.
Note Types of Damage and Take Action
Breakage
Breakage is the most common type of storm damage. Its impact depends on the degree and pattern of
damage as well as the tree species involved. Breakage inevitably lowers timber values. Breaks are
uneven by their nature and occur randomly along the tree bole. The random pattern lowers value since
products are normally cut in specified lengths. Breakage also lowers value because difficulty in logging in
broken timber slows productivity. Patterns are important when assessing breakage impact. When ice or
strong gale-force winds break trees, break patterns are simple and limited to the area adjacent to the
breakpoint. Hardwood trees are seldom killed by breakage. Even when tops are completely gone, new
branches will sprout and the tree will recover. In hardwoods, the major problem is that breaks in the
trunk or large branches (over 3 in. diameter) permit entry of stain and decay fungi. Stain will move
vertically from the injury at a rate of 6 to 18 inches per year, and decay will follow the stain in 8 to 10
months. Most species of pine will die if tops are completely broken and no live limbs remain. If three or
more live limbs are left in the tops of loblolly or slash pines, the chance of survival is excellent (above 75
percent). One of the lateral branches in these trees will become the terminal, and in 8 to 10 years the
only sign of breakage will be a sharp crook in the bole at the point where the break occurred. These
trees will experience growth losses, however.
Recommendations
For hardwoods, trees with broken tops or branches over 3 inches in diameter should be salvaged during
the next scheduled harvest. High-value trees such as those in recreation areas and in yards should be
properly pruned to promote rapid healing. For pines, if three live limbs or less remain, the trees should
be harvested as quickly as practical.
Figure 4. Pine tree with broken main stem.
Twisted Trunks
The cyclonic winds that are typical of tornadoes, and often accompany hurricanes, cause twisting and
separation of wood fibers in the main stem. Logs from trees that have experienced this treatment may
fall apart when sawn for lumber products. Trees twisted by cyclonic winds may appear normal, except
that pines often have pitch flow along the trunk.
Recommendations
Trees with evidence of twist injury should be removed, since the problem will not disappear with time
and considerable losses may be incurred during a later harvest.
Root Damage
If they are not salvaged promptly, uprooted trees probably will be degraded quickly by stains, decays,
and secondary insects, such as Ips bark beetles, borers, powderpost beetles, and ambrosia beetles. The
longer salvage is delayed, the greater the amount of degrade and weight loss from rapid drying. Degrade
translates into a stumpage value loss. The amount of degrade that is acceptable to industry depends on
the tree species and local markets. Table 1 shows the probable sequence of invasion by damaging
organisms in storm-damaged timber.
Figure 5.
Figure 6. Internal stain on a previously damaged tree.
Table 1. Sequence of invasion of damaging organisms in storm-damaged timber
Species Year 1 Year 2
Pine
Bark beetles, ambrosia beetles, sawyers,
blue stain fungi, soft rot fungi
Decay fungi
Oak and hickory
Wood borers, ambrosia beetles,
Sapwood decay fungi
stains, soft rot fungi
Other hardwoods
Wood borers, ambrosia beetles,
stains, soft rot fungi
Sap and heartwood
decay fungi
Root-sprung trees will not die immediately, but will show decline symptoms over a period of several
years. These trees may be invaded by root rot organisms and subjected to drought stress and insect
attack. Root-sprung pines may be invaded by bark beetles and blue stain fungi. These pines can serve as
prime habitat for the southern pine beetle and, if conditions become favorable, an outbreak could
occur. They can also harbor high populations of turpentine beetles.
Recommendations
Trees with major root damage should be salvaged as soon as possible to avoid growth loss, product
degrade, bark beetle attacks, and mortality.
Major Wounds
During storms, many trees sustain wounds, caused by falling tops, adjacent uprooted trees, and major
branch breakage. In hardwoods, wounds that do not penetrate more than 2 inches into the sapwood
and have less than 144 square inches of surface area will have only localized stain, but little decay.
Wounds that exceed these limits will have stains and decay that move at the rates described for broken
branches. Pine trees with major wounds to the lower bole and larger roots may be attacked by bark
beetles.
Figure 7. Wounds associated with storm damage.
Recommendations
Trees with major wounds should be considered for removal during the next scheduled harvest, or they
should be included in the salvage operation.
Bent Trees
Bent hardwoods usually are not attacked by insects or diseases because they are not in a stressed
condition. Pine trees that are bent to the extent that cracks and resin flow occur may be invaded by bark
beetles and disease-causing organisms.
Figure 8. Trees bent during a hurricane.
Recommendations
Small trees (under 15 feet in height) usually straighten even after severe bending. Taller severely bent
hardwoods should be removed during the salvage operation or the next scheduled harvest. Be sure to
inspect large pine timber for pitch flow. Many large, green, standing trees may not be usable for veneer,
poles, or lumber because of internal ring shake, splintering, and separation of the wood fibers. Often,
the only external evidence of such damage is pitch or sap flow where the injury has broken the bark.
These characteristics are often overlooked, and considerable losses are incurred during a later harvest.
Standing Water
In standing water, the dissolved oxygen is quickly depleted, so trees of most species are injured by
prolonged flooding, particularly during the growing season. The loss of soil oxygen leads to root
mortality and tree death. Trees weakened by standing water are often attacked by insects or affected by
diseases.
Figure 9. Trees killed by standing water.
Recommendations
Forest managers may wish to favor flood-tolerant trees and shrubs in areas subject to intermittent
flooding. Tree species that can tolerate prolonged or intermittent flooding are noted in table 2. Floodtolerant shrubs include: buttonbush, sand plum, deciduous holly, and swamp-ironwood.
Table 2. Utilization guidelines for beetle-killed pine trees
Product
Class A Class B Comments
Trees with needles
Trees with no needles,
or no needles, most twigs and
but twigs attached
branches lost, and
some broken tops
Appearance
Not recommended
Not recommended
Blue stain prohibits use
lumber
Dimension
Can be used
Not recommended
Should be kiln dried to prevent
lumber with caution
emergence of secondary insects.
(structural)
Low moisture content may dull
saws and chipper knives faster than
with sound wood and may require
milder kiln schedule. Do not use
where toughness is important.
Decorative
Can be used
Can be used
Should be kiln dried
lumber boards
and paneling
Posts, poles,
Not recommended
piling
Not recommended
Toughness and preservative
treatability may be highly variable
Plywood
Can be used
Not recommended
Adhesives and gluing practices
may have to be adjusted
Hardboard,
Can be used
particle-board,
Can be used
Low moisture content may affect
some production schedules.
medium density
Should be mixed with sound wood.
fiberboard
Pulp
Can be used
Can be used
Blue stain and low moisture
content may affect pulping
process and chemical or energy
requirements. Should be mixed
with sound wood, particularly
where strength is important.
Fuelwood
Can be used
Can be used
Low moisture content increases
heat value
Manage to Reduce Pest-Caused Losses
Storm damage often increases the risk of pest outbreak by weakening the defenses of host trees. Pest
infestations will not develop unless suitable host trees are available, so every effort should be made to
remove concentrations of susceptible host trees. A well-planned and executed salvage operation can
greatly increase a stand’s resistance to pest attacks. To ensure effective salvage, we recommend the
following approach:
1.
Act quickly. Prompt salvage will help avoid losses from degrade and subsequent pest-caused
mortality.
2.
Measure carefully the extent of the damage before deciding on a salvage operation. A number
of factors such as stand age, species, stocking, and management objectives will need to be considered.
3.
Salvage the most severely damaged timber first. Concentrate on the pine stands, because they
are more susceptible than hardwoods to pest outbreaks. On deep sandy soils where a stand will be left,
the stumps should be treated for annosus root rot control. During salvage avoid damage to residual
trees.
4.
Complete salvage promptly and in one continuous operation. Bark beetle populations are more
likely to build up in the slash and move into healthy trees if logging operations are prolonged or
interrupted for periods of a month or more. (When salvage is delayed, a helpful guide is available for
utilization of beetle-killed pine trees based on tree appearance. See table 2.)
5.
Follow the practices listed below to ensure that the residual material (slash) will dry quickly.
Bark beetle infestations will not build up in dry material.
•
Cut all logs from seriously damaged trees to the minimum merchantable size and remove them
from the area.
•
Lop and scatter all harvesting slash and tops into open areas when possible.
•
Scatter large accumulations of slash away from the bases of residual trees, and into direct
sunlight if possible.
•
Sever downed trees from roots that could keep them alive.
6.
Inspect large pines for pitch flow. Many large, green, standing pines may be unusable for
veneer, poles, or lumber because of internal splintering and separation of the wood fibers. Often, the
only external evidence of such damage is pitch flow where the bark has been broken.
7.
Follow the ratings of species resistance to insects and diseases in table 3 when planning the
salvage of timber, especially hardwoods.
Table 3. Resistance of tree species to huricane-related damage
(in descending order of resistance)
Flood
tolerant
Deterioration
Breakage
Uprooting
Salt
by insect
and disease
baldcypress
live oak
live oak
pondcypress
palm
tupelo-gum
baldcypress
palm
palm
live oak
live oak
slash pine
sweetgum
palm
baldcypress
sweetbay
pondcypress
willow sweetgum
pondcypress
tupelo-gum
longleaf pine
pondcypress
water oak
sycamore
sweetgum
tupelo-gum
redcedar
loblolly pine
baldcypress
sycamore
mimosa
sweetgum
redcedar
pondcypress
river birch
dogwood
sycamore
tupelo-gum
southern red oak
cottonwood
magnolia
longleaf pine
baldcypress
magnolia
green ash
sweetbay
mimosa
sweetgum
tupelo-gum
red maple
southern red oak
pecan water oak
mulberry
magnolia
sycamore
southern red oak
sycamore
water oak
hickory
slash pine
sweetbay
American elm longleaf pine
loblolly pine
southern red oak
persimmon
slash pine
sweetbay
hickory red maple
silver maple
loblolly pine
water oak
mimosa
water oak
redcedar
red maple
pecan dogwood
swamp chestnut oak
magnolia
hickory dogwood
red maple
hickory pecan pecan dogwood
pecan
redcedar
mimosa
magnolia
hickory red maple
sweetbay
longleaf pine
slash pine
loblolly pine
8.
Consider deducting storm-damage losses on income-tax returns. Landowners can secure advice
from local foresters, accountants, attorneys, or Internal Revenue Service agents concerning deductible
losses.
9.
Check for pest activity after salvage operations are finished. Make periodic surveys, either aerial
or ground, of the residual stands to check for pest activity. These surveys may be required for up to 2
years. Trees that are turning yellow, have pitch tubes on the bark, or red boring dust around the base,
are probably affected by insects, diseases, or both. These trees should be considered for control
activities.
Figure 10. Bark beetles often kill weakened trees.
Manage to Reduce Hurricane Damage
Tree species vary in their ability to withstand hurricane winds and salt damage. Wind resistance depends
on the interaction of five factors: strength of the wood, shape and size of the crown, extent and depth
of the root system, previous moisture conditions, and shape of the bole.
No tree species has perfect wind resistance, but live oak, palm, pondcypress, and baldcypress are among
the best, as shown in table 3. These trees combine deep root systems with buttressed trunks (low center
of gravity). The wood of live oak is exceedingly strong and resilient. The crown is usually widespread, but
this does not seem to negate its strong points. Cypress has relatively weak wood, but its crown is so
sparse and its foliage so limber that it is also extremely windfirm.
Shallow-rooted trees are easily uprooted, especially after the soil is saturated by heavy rains. Common
shallow-rooted trees along the coast are dogwood, water oak, pecan, sweetbay, and red maple.
Common deeprooted trees are live oak, longleaf pine, and pondcypress and baldcypress.
Trees growing in sandy soils are more deeply rooted than trees growing in soils with an inhibiting clay
layer or a high water table. Although rooting habits vary according to the soil profile, each species has a
characteristic pattern. Another factor to be considered is the height of the tree. The taller the tree, the
greater is its chance of breaking, especially if the bole has little taper. For this reason, tall, slim slash and
longleaf pines are extremely vulnerable.
Open-crowned and lacy-foliaged trees, such as cypress and mimosa, offer less resistance to the wind,
and thus are better able to survive. On the other hand, magnolia trees with their heavy, wind-catching
foliage are windthrown more than their root system and bole structure would indicate. Palm trees offer
little surface to the wind because they have almost no laterally extended crown and branches. This
characteristic makes them fairly windfirm, despite their limited root systems.
Based on these observations, the following preventive measures are recommended to forest managers
in hurricane-risk areas:
1.
Keep a balanced mixture of size and age classes to prevent a complete loss. Young trees are
rarely damaged, because they tend to bend with the wind; old trees tend to break or uproot.
2.
Where feasible, stagger thinnings to limit exposure of the recently thinned areas. (During
Hurricane Camille, recently thinned stands of pine with little taper were severely broken, while open
stands and stands thinned several years earlier suffered less damage.)
3.
Manage for well-spaced, thrifty trees and, as much as possible, develop a spread of age classes
to distribute the risk of wind damage.
4.
Consider planting longleaf pine in deep sandy soils, because longleaf has a deep taproot.
5.
When planting slash and loblolly, use an 8- by 8-foot or wider spacing.
Winds often carry saltwater inland for a considerable distance. The leaves on trees saturated with
saltwater turn brown and give the appearance of being burned. Most of these trees will not die and
should not be cut. See table 2 for resistance among tree species. The trees may lose their leaves and
some growth, but most of them will grow new leaves and recover. Check trees closely in the spring after
salt damage for adequate recovery or possible bark beetle attack. Trees should be harvested if they
have been attacked by bark beetles or if they have not put on new growth in the first full growing
season after the damage occurred.
Figure 11. Salt-damaged pines.
Figure 12. Back cover.
Decay Following Glaze Storm Damage in Woodlands of Central New York
Extension
Journal of Forestry
Perley Spaulding and Allen W. Bratton
REF# 390
Northern hardwood stands in Otsego and Herkimer Counties, New York were severely damaged by an
ice storm in December, 1942. Early in 1945 saprot had developed at the bases of injured but living sugar
maple and beech trees. The initial injury appears to be due to sunscald caused by sudden opening of the
stands. The silvicultural significance of the saprot fungi found attacking injured trees is indicated.
Silvicultural measures for handling these stands are given.
An ice storm of remarkable intensity and duration occurred in December, 1942, over an extensive area
in New York, New England, and Canada. Field observations and reports of sawmill operators in the area
early in the summer of 1945 showed that saprot of the main stems of sugar maple and beech was
becoming serious. A brief survey of the deterioration of living trees was made in July in northern Otsego
and southern Herkimer Counties, New York, at higher elevations where the glaze storm damage was
most severe. Two and one-half years, (two full growing seasons and part of another), had elapsed since
the storm.
Immediate Damage
Starting during the evening of December 27, 1942, and reaching its peak on the 30th, rain together with
freezing temperatures provided just the right conditions for the formation of ice on trees (5). The storm
was followed by eight inches of snow, accompanied by winds of 25 miles per hour. There was no real
melting of ice on the exposed limbs of trees for more than two weeks. Another similar but lighter storm
followed on the 18th and 19th of January with extreme cold on the 21st of January, 1943.
The glaze increased with elevation and was more prevalent on the eastern slopes. In reporting on
damage to power and light lines (5), it was found that little damage was done at elevations below 500
feet. At 500 to 1,000 feet, the glaze was one-half to one inch in radial thickness. At elevations of 1,000
feet and over, the radial thickness was 1 1/4 to 2 1/2 inches and in some cases, more than 3 inches.
Analogous conditions of ice on trees were observed at the time of the storm. Damage to the ice laden
trees varied from the loss of a few branches to complete stripping of all branches or to breakage of the
main stem either in or below the crown. Smaller trees, too flexible to break, were bent over until the
crowns touched the ground, or were uprooted (Fig. 1).
Figure 1. A damaged stand just after the storm. Small trees bent to the ground; larger trees with most of
the branches broken off.
In the affected area all tree species suffered in some degree, with the original injury bearing a direct
relationship to species, crown form, and size. Sugar maple, beech, white ash, and basswood were about
equally broken by the ice-mute testimony to the immense weight of the glaze coating, which on some
power lines were found to weigh as much as 14 pounds per linear foot. The worst affected stands were
composed of sugar maple, beech, white ash, basswood, and small numbers of other hardwoods with
occasional white pines. Sugar maple and beech were most abundant. Much damage occurred in stands
of sugar maple and beech averaging about 10 to 16 inches d.b.h., usually considered too small for
sawlogs. Mature white pine was badly injured with tops completely removed or branches partially
broken out. Damage to hemlock was of such a minor character as to be considered negligible. In
plantations, red, Scotch, and white pines lost leaders, laterals, and in some cases entire tops, or the
trees were pressed down into a horizontal position by the weight of the ice. Norway spruce and
European larch apparently suffered less than the pines. These conditions were found to parallel those
resulting from a storm in 1936 that damaged the forests on six million acres in Pennsylvania and New
York (6). Abell (1) reports a similar occurrence in the southern Appalachians.
Later Damage
The storm left the forest floor so littered with broken branches and tops and with trees bowed over or
uprooted that very few attempts were made on the part of owners or loggers to do any salvage work.
When the woods became more accessible, due to the breaking down of debris, salvage operations were
begun. By June 1945, reports were received of deterioration caused by saprot fungi.
After a lapse of two and one-half years, the reaction of sugar maple, beech, white ash, and basswood to
the heavy top damage is striking. Very abundant sprout growth is present in the tops of white ash and
basswood, even when stripped of all branches (Fig. 2). This renewal of the tops together with the typical
thick rough bark of these species appears to have prevented dying of the bark on the main stem and
infection there by saprot fungi. Beech sprouted somewhat less vigorously, still new growth was
adequate to prevent infection of the main stem except in a few instances. Sugar maple sprouted even
less. Badly injured trees evidently could not replace foliage sufficiently to maintain life throughout such
trees (Fig. 2).
Figure 2. A damaged stand 2 1/2 years after the storm. Most of the dead and badly broken trees are
sugar maples. The two bushy trees back of the large sugar maple in the left foreground are white ash or
basswood with profuse sprout development replacing their broken branches.
Changes In Environment
The environment of the surviving trees was changed abruptly, the amount of change depending on the
severity of damage to the stands. Interrelations within the forest association were upset and even
largely destroyed, composition of the stand was greatly changed, and adverse soil conditions were
created temporarily. The most obvious and destructive effect was that of breaking up the crown cover
and suddenly exposing trunks and soil to the full heat and drying of the sun (Fig. 2). This prevailed only
the first summer, as luxuriant ground cover soon shaded the ground and partially restored the former
coolness and moisture. The exposed trees suffered severe physiological shock, if not actual visible injury,
in the case of the tolerant immature sugar maple and beech.
Saprot In The Lower Trunks of Sugar Maples And Beeches
Saprot running upward from a point near ground level, but with no evident external bark injury as an
entry point was found in sugar maple, and to a lesser extent, in beech. Fungus fruiting bodies were
plentiful on the dead bark. Far the greater number were newly formed ones of the current season, but
usually a few old ones of the preceding year were present on small patches of blackened bark near
ground level (Fig. 3.). These patches evidently died and were infected first. It is known that a number of
the common saprot fungi found on the damaged trees begin to fruit within a minimum of two growing
seasons in new slash. Hence, the areas of bark with old fruits must have been injured and died before
midsummer following the storm. The injury may have occurred in an early spring warm spell or later
during the first hot spell.
Figure 3. Daedalea unicolor fruiting on sunscalded living trees. A. sugar maple. Note blackened area near
base. B. beech. Note small canker near upper left side, well separated from main canker, and indicating
parasitic action.
Data taken on damaged living trees that were examined showed that (1) saprot was much worse in
sugar maple than in beech, while there was little in white ash or basswood; (2) saprot damage occurred
mostly in trees with 85 percent or more of the crown broken out; (3) the injury was almost entirely on
the southern and southwestern sides of the trees; (4) with few exceptions the saprot was noted in trees
18 inches or less in diameter, i.e., in sugar maple trees with relatively thin rough bark.
Dying of bark in smooth, thin-barked trees when suddenly exposed to the sun’s rays is common and well
known to orchardists and foresters. It is not entirely limited to smooth barked trees. While sunscald of
sugar maple in forest stands is a new thing in our experience, it appears from experience with shade
trees that sugar maple is somewhat susceptible to such injury. The environment of shade trees often is
much more adverse than that in forest stands. According to shade tree specialists, Stone (9) and Felt (7),
sugar maple is quite susceptible to sunscald in rough barked street trees. Location of the patches of bark
longest dead near or at the bases of the affected trees suggest that heat reflected from bare soil caused
the injury. Thin ground cover or entire lack of it would favor reflected heat and resultant sunscald. The
available evidence indicates that sunscald in some form killed the patches of bark that died in the first
season and was the direct cause of a moribund condition or actual death.
A significant fact is that Daedalea unicolor was fruiting on nearly every saprotted tree, and evidently was
one of the first fungi to attack them (Fig. 3). This might indicate attack in bark not yet completely dead,
as this fungus is known to be aggressively parasitic. Campbell (3) found it infecting sunscald areas on
roadside trees as well as heat injuries caused by slash fires.
Development of Trunk Rot From Crown Wounds
Decay extending into the trunk from breakage wounds in the crown will be of two types: saprot and
heartrot. The former may originate in the sapwood of the open wound, or in dead, intact bark below the
wounds. In the first case, establishment of the fungus in the sapwood may be delayed a few years by the
dryness of the exposed wood, but may become evident in the trunk within 5 years. Infection in the dead
bark below wounds is a common occurrence. Soon after relatively large branches are broken out, some
of the bark just below the wound is likely to die from interrupted sap conduction. Usually, the patch of
dead bark is roughly triangular with the tip downwards. A similar, but usually less extensive, dead patch
may form above the wound also, but with the tip pointing upward. Numerous saprot fungi readily attack
such dead bark and soon extend into the underlying dead sapwood. This saprot is likely to develop
within a rather short time, and may become damaging in the trunk within 5 years. The rate of its
progress depends upon the fungus causing it and the natural rot resistance of the tree species.
Heartrot fungi are quite different from the saprot fungi. They attack the heartwood exposed in open
wounds and appear to progress less rapidly in the infected wood. Usually, they require about twice as
long to cause damage as do the saprots. Progress of the decay depends on the fungus causing it and the
natural decay resistance of the heartwood of the tree species.
Damage by a severe glaze storm in 1936 has been mentioned (6). Studies of decay following this storm
were made in Pennsylvania by Campbell (2) about 6 months afterwards, by Sleeth (8), 19 months after,
and by Campbell and Davidson (4), 4 years after the storm. They found various saprot fungi attacking the
wood in large breakage wounds and much variation in susceptibility of tree species to saprot.
Fungi Causing Decay and Their Significance
A number of different fungi were found fruiting on the lower trunks of surviving hardwood trees, but
mostly on sugar maple and beech. No fungus fruits were noted in the injured crowns. These fungi were
of the so-called saprot-producing species. They were Daedalea unicolor, Peniophora sp., Polyporus
adustus, P. hirsutus, P. pargamenus, P. tulipiferus, P. versicolor, and Schizophyllum commune. Further
search probably would reveal others, but these were the common ones.
Daedalea unicolor was present on practically every saprotted tree, evidently first attacking the dead
patches of bark near ground level and spreading rapidly upwards, and sidewise to a lesser extent. Its
parasitic ability enabled it to be the first fungus present in most injured trees and its rapid progress
enabled it to crowd out most of the other fungi that attacked later. Once it gains entry to a living tree, it
is known to continue until the tree is killed (3) hence, all trees found bearing its fruiting bodies should be
salvaged as soon as possible to prevent total loss. Moreover, there is high probability that breakage
wounds in the crowns will develop rot by this fungus, as it appears to be unusually abundant in this
locality.
Schizophyllum commune was second in abundance, but decay caused by it was slight, extending only a
few annual rings in depth. It is favored by open sunlight and relatively high temperatures, conditions
that account for its abundance in the surviving trees. Of itself, it is of little significance, but it does
indicate the probable appearance of other saprotting fungi in the near future.
None of the other species found is known to attack living tissues. Their presence indicates saprot is well
under way and prompt salvage will prevent more extensive damage. Many of the affected trees will
survive indefinitely, but decay will increase steadily until the entry wound healed. Then the fungus
often becomes inactive or dies (2).
Management of The Surviving Trees
The storm damage had the general effect of a heavy thinning in the hardwood stands. Where grazing
had been prohibited, a remarkable release of existing reproduction and the establishment of new
reproduction has resulted. Fortunately too, much of this reproduction is of desirable species.
The natural hardwood stands should be managed on a selective basis with such modifications as will
permit the salvage of merchantable material that will not go through a cutting cycle without material
loss in increment and quality. In general, this will mean the salvaging of all material in the badly broken
stands where any residual stand that might otherwise be left will be too sparse to permit profitable
operation in a subsequent cut. In stands where the badly broken trees are scattered, all such trees
should be promptly cut and utilized. In the selection of individual trees consideration should be given to
the probable future of the different species.
Sugar maple does not sprout sufficiently to replace lost branches to any extent. Trees with less than half
of the crown now alive are not likely to resume vigorous growth. They will continue to die year after
year for some time. At best, such trees are not likely to add increment fast enough to justify holding,
with the possible exception of those now nearing sawlog size, the holding of which for a few years might
mean their devolopment into a considerably more valuable size class. Saprot in the butt will probably
develop in some trees that have not yet shown it, but the number of such trees will be small. However,
rot is likely to run downward from large broken branch stubs in about ten years.
Beech should be selected on about the same basis as sugar maple. Though sprouting is a little better, rot
is likely to progress faster from large branch wounds. The market for beech sawlogs has generally been
less attractive than for sugar maple and the selection of beech for cutting should be directed toward the
removal of as many as possible of the damaged trees that do not give promise of vigorous growth.
The sprouting of basswood has been so profuse that broken crowns have been largely replaced and
saprot at the butt is negligible. Such trees are likely to add increment and can be held about ten years to
obtain merchantable size. Rot from above is likely to run downward in about ten years, so that plans to
hold them longer than that are inadvisable.
The management of white ash should be the same as that for basswood except that, because of greater
resistance of the wood to rot, this species can be held considerably longer before rot runs down from
large branch wounds.
Literature Cited
1.
Abell, C. A. 1934. Influence of glaze storms upon hardwood forests in the southern
Appalachians. Jour. Forestry 32: 35-37.
2.
Campbell, W. A. 1937. Decay hazard resulting from ice damage to northern hardwoods. Jour.
Forestry 35: 1156-58.
3.
--. 1939. Daedalea unicolor decay and associated cankers of maples and other hardwoods. Jour.
Forestry 37: 974-77.
4.
--. and R. W. Davidson. 1940. Top rot in glaze-damaged black cherry and sugar maple on the
Allegheny Plateau. Jour. Forestry 38: 963-65.
5.
Christie, E. J. and H. S. Chartier. 1943. Glaze storms and electrical service. Electrical Engineering
62: 431-35.
6.
Down, A. A. 1938. Glaze damage in the birch-beech-maple-hemlock type of Pennsylvania and
New York. Jour. Forestry 36: 63-70.
7.
Felt, E. P. 1941. Pruning trees and shrubs. 237 pp. New York.
8.
Sleeth, Bailey. 1938. Decay in black cherry damage by glaze. Allegheny Forest. Expt. Sta. Tech.
Note 20. 2 pp. [Mimeo.]
9.
Stone, G. E. 1916. Shade trees, characteristics, adaptation, diseases and care. Mass. Agric. Expt.
Sta. Bul. 170: [123]-264, illus.
Storm Damages Sugar Bushes
Extension
Maple Syrup Digest
Leland Schuler, County Agent, Burton, Ohio
Vol. 8, No. 4
October 1969
REF# 105
Fourth of July Storm causes excessive damage to sugar bushes in Geauga County.
1969 in Geauga County, Ohio, will be remembered as one of the wettest years in weather history. July 4,
1969 will be long remembered as one of the worst cyclone storms in northern Ohio. Geauga and lake
counties caught the brunt of the wind storms and farther south and west parts of Erie, Holmes, Ottawa,
Sandusky, Seneca, Medina, Lorain, Ashland, Huron, and Wayne counties were nearly washed away with
torrential rain storms.
The windstorm and tornadoes caused damage to sugarbushes and woodlots in an area approximately
six miles wide and twenty miles long from northwestern Geauga County to the southeastern part of the
county.
Damage in individual sugarbushes varied from 25 to 50 trees, to entire woodlots of 55 or 60 acres. An
unofficial estimate of 20 million board feet of salvage timber was made about a week after the storm.
The estimate indicated as high as 70% of this salvage timber was maple. Burton park looked like a
battlefield after the big storm. Most communities were without electric power or telephones from one
to seven or eight days.
Figure 1. Woodlot on Aquilla Road owned by city of Akron.
Figures 2 and 3. Burton Park Sugarbush (figure 2 and figure 3) shows force of July 4th storm.
Figure 4. Charles Vanac sugarhouse and sugarbush.
The State Forestry Division of the Ohio Department of Natural Resources responded almost immediately
to the storm by sending Farm Foresters from all over Ohio to assist sugarbush and woodlot owners to
survey the damage and begin the marking and grading of salvage timber. The Division is to be
congratulated for their understanding and recognition of the Disaster. At the present time, there are
eleven Farm Foresters working in Geauga County in the sugarbushes and woodlots.
Almost miraculously no one was seriously hurt, or killed in the storm. Our sugarbushes took the brunt of
the storm. Although there was damage to homes and buildings from fallen trees and wind movement
we were fortunate that the trees helped break the fury of the storm.
Most of our Geauga County residents had little or no warning of the severity of the storm. It developed
in Lake Erie and below the Canadian border so most of us were unprepared for what followed.
The real storm damage occurred in the county at about 8:30 P.M. Ture Johnson, National Maple Council
president, and his family were in northern Michigan on vacation. My wife and I were just preparing to
take a few days off on a trip to Lancaster county, Pennsylvania. We planned to leave the morning of July
7 after the holiday rush and traffic. We did not make it to Lancaster county, Pennsylvania until the
following weekend.
Most of the National Maple Council know that we have a very small sugarbush at the back of our home
on Hale Road in Burton township. It is hard to describe one’s feelings and one’s actions during a time of
stress such as the July 4 storm.
The storm started much as any thunderstorm starts as the temperature and humidity builds up in the
late afternoon. The wind was out of the southwest and kept increasing in velocity to about seventy miles
per hour The skies became increasingly dark and mean looking. Suddenly the wind died to almost a
calm. At a distance you could hear the fury of the wind building from the northwest. It was then I told
my wife that we had better move to the basement of our home. I had an awful time convincing her since
there had been no announcements on television or the radio.
My wife, Marjorie decide to accompany me to the basement when she heard the crashing of falling
trees and breaking limbs in the distance. I managed to open the door on the east side of our home
before the full storm hit us. If you have never been in a wild storm next to a sugarbush you have no idea
of the sounds of crashing trees and the violent turbulence of the trees. I lost twenty-five trees on our
small acreage and am just now after a month able to say that the cleanup is nearly over. I spent three
days after the storm digging out the debris in our back yard. A few hours each day with a chain saw have
helped to clean up the worst of the debris. Dan Wengerd, our neighbor, helped me to pull some of the
lodged trees out of others that were still standing, with a tractor.
Volunteer workers appeared after the storm to help clear roads and remove trees from parks, damaged
homes, and buildings. Some of us that were without electricity had to find freezing facilities for our
frozen food. Water was at a premium since pumps will not work very well without electricity.
Each county in the United States has a disaster committee that functions in an emergency such as ours.
The disaster committee of the USDA went to work a few days after the storm. A special meeting was
called of ASCS township and county committeemen on July 14 to survey the extent of damage to
cropland, sugarbushes, and farmsteads. Total loss of income for maple syrup, grain and hay crop
production and loss in value of timber stand and orchards plus added expenses to farmers replacing
fences and repairing damaged buildings was estimated to approach or exceed the two million dollars
figure over the next five or six year period.
A special emergency ACP debris removal practice was written by the State and County ASCS offices for
Sugarbushes, Orchards, Vineyards, and Small Fruit plantings to help get them back into production.
These emergency practices were submitted to the Federal ASCS office for their approval, at the highest
level of assistance possible, for Geauga and Lake counties. The State ASCS office will be able to
announce these practices as soon as it has received final approval from the USDA.
The Geauga County Extension Forestry Committee called an emergency, study meeting of the
committee, other agricultural agencies, and foresters from the Division of Forestry, and Ohio State
University on July 29. A tour was made of some of the storm damaged sugarbushes and woodlots. In the
afternoon the group discussed the situation and made their conclusions.
The recommendations and agreements of the study group were as follows:
1.
To urge sugarbush owners to have salvage lumber in the buyer's yards by the first of the year.
2.
To prepare a list of buyers that are interested in salvage lumber.
3.
To ask for more farm foresters help in marking trees provided more woodlot owners contact the
Farm Forester's office for assistance.
4.
To ask for a priority on marking sugarbushes since sap trails will need to be cleared for next
spring's maple season.
5.
To ask the ASCS committee to prepare a special ACP practice on debris removal on sap trails in
sugarbushes.
6.
To send a special letter to sugarbush owners and woodlot owners about salvage lumber disposal
and debris removal procedure and include a list of buyers of salvage lumber.
7.
To prepare lists of owner's with amounts of salvage lumber and species for sale that can be
distributed to buyers and distant sawmill operators.
8.
To arrange a special meeting of sugarbush owners and the Internal Revenue Office to help
develop an income tax ruling on loss deductions for the July 4 storm.
The Maple Syrup Industry in Geauga County has been dealt a severe blow, by Mother Nature, but we
are still planning on hosting the National Maple Syrup Conference at Punderson on October 20, and 21.
Hope to see you there.
Drought
Frost
Can Cold Weather Negate Bud Effects
Extension
Maple Syrup Digest
Robert R. Morrow, Cornell University
Vol. 12, No. 2
July 1973
REF# 073
The 1973 maple syrup season, with its early March heat wave, was most unusual. Temperatures
averaged 15° F. above normal during the first half of March at Lake Placid, New York. Half a crop of
syrup was made prior to the usual date of the first sap flow. A normal season's accumulation of heat
(summation of mean temperature times duration for portion of day above 35° F.) occurred by early
April. Bud break appeared near.
This sequence of events followed:
a.
March 30 - April 4. Generally warm, temperatures ranged from 31 to 60° F., mean 40° F.
b.
April 5 - 6. Mostly freezing weather, mean 29° F.
c.
April 7 - 10. Sap flow weather, mean 30° F. Syrup became progressively poorer. April 10 sap,
with a sugar percent of 1.5 made light amber syrup, but the boiling sap had an off-smell and the syrup
an off-flavor. A buddy test was positive.
d.
April 11 - 13. Very cold, mean 20° F. Collecting tanks were cleaned.
e.
April 14 - 16. Sap flow weather, mean 37° F. This flow followed nearly 90 hours of freezing
weather. Sap sugar was only 1.4 percent. There was no off-smell nor off-flavor, and three drums of good
table grade syrup were made from this thin sap.
Apparently the sharp cold preceding the last run negated the effects of earlier bud activity. The cold was
both intense and of long duration. Others have also reported that they believe late cold spells this year
negated bud activity.
Acid Precipitation
Is Acid Rain A Threat
Research
Maple Syrup Digest
Lyle S. Raymond, Jr. Cooperative Extension, Cornell University
Vol. 22, No. 4
December 1982
REF# 168
So far, acid rain effects on trees have not been observed otherwise than under simulated laboratory
conditions. Forest effects from acid rain under natural conditions that can be directly traced to acid rain
have not been found. It can only be said that effects observed in laboratory experiments might occur
under natural conditions.
Furthermore, the laboratory experiments have produced mixed results. Some trees are harmed by acid
rain; others show no effect at all; and some grow better.
Perhaps we shouldn't be too surprised at this, for the various tree species are naturally adapted to a
wide range of growing conditions, including natural variations in soil acidity. Observed effects also differ
according to the stage of growth of the tree, and the specific amounts of simulated acid rain applied at
these different growth stages.
Coniferous trees have received the most attention in acid rain experiments. I will focus upon
experimental results with deciduous trees, due to the interests of the people here. So far, these
experiments have shown the following general results:
•
Some leaf, seedling and germination damage to deciduous trees has been observed in some
species with simulated acid rain at Around pH 3.0 or lower. (Rainfall pH in the North east and eastern
Canada is 4.0 to 4.5, with some rainfalls as low as 3.5)
•
Yellow Birch seems to be quite sensitive to acid rain
•
Red Maple appears to be somewhat sensitive
•
Sugar Maple appears to be rather acid-tolerant
•
A recent study of simulated acid rain effects on Sugar Maple at the State University of New York
College of Environmental Science and Forestry was reported in the publication Environmental and
Experimental Botany this month (October 1982). This research, performed by Dudley J. Raynal, J.R.
Roman and W.M. Eichenlaub, shows little effect on Sugar Maple seed germination but some damage to
seedlings at pH 3.0 or lower.
Since Sugar Maple seedlings start under the snow cover and Spring snow melt water contains the winter
accumulation of acids from snow storms, the study recommends further investigation of possible low pH
effects on Sugar Maple seedlings from snow melt runoff.
I'd like to mention a couple of current studies that I know about. Both include Sugar Maple and reports
from both studies will be available next year.
The first is the FORAST study of tree ring cores in 10 eastern states to see if changes in growth rates can
be detected over a 50-year period. Paired sites for obtaining tree cores are being used. One of each pair
of sites is on acid soil and one on soil that is not acid. The paired sites are situated close enough together
so that they receive the same rainfall.
The FORAST study is funded by the U.S. Environmental Protection Agency through the Oak Ridge
National Laboratory. This is an attempt to obtain data under natural conditions , rather than by
laboratory experiments. (FORAST stands for Forest Responses to Anthropogenic Stress.)
In the second study, funded by the U. S. Forest Service, the combined effects of acid rain and ozone on
Sugar Maple are being investigated. This work is being done at the Boyce Thompson Institute for Plant
Research at Cornell University.
Conclusions
No direct proof of forest effects from acid rain under natural conditions has been found. This does not
mean that none will be found in future studies, of course.
Available evidence of harmful effects to trees from acid rain has been extrapolated from experiments
under controlled conditions with simulated acid rain and assumed processes affecting trees.
Scientists say that it will probably take years to develop verifiable answers as to whether acid rain is
adversely affecting trees.
Where does that leave us? It appears that whether "something should be done now about acid rain"
may depend more upon other observed effects - such as to lakes and streams - than upon demonstrated
forest effects, and upon how we feel about acid rain generally as an environmental issue.
Woodlot Management
Grazing
Soil
Topography
Competing Vegetation
Tree Condition
Stand Condition
Decline Comply
Current Research on Sugar Maple Decline at The University of Massachusetts
Research
Maple Syrup Digest
John H. Noyes and Arthur H. Westing
Vol. 3, No. 4
December 1964
REF# 148
Impetus to the current program of research being conducted on sugar maple decline at the University of
Massachusetts was provided by State Representative John D. Barrus of Goshen (Second Hampshire
District). During the 1963 legislative session Representative Barrus contacted Dr. Arless A. Spielman,
Dean of the University's College of Agriculture, about the obvious situation that many of the sugar
maples of our Commonwealth had become unhealthy and were in some instances dying. As a member
of Gov. Endicott Peabody's Committee on Natural Resources, Representative Barrus had received
numerous calls and letters from many parts of the State about declining sugar maples and had
confirmed these reports with observations of his own.
A careful preliminary evaluation of the sugar maple decline situation in Massachusetts by
Representative Barrus in conjunction with the University brought to light that the decline has been
prevalent for several years, that it is particularly widespread among roadside and sugar-bush trees, and
that its cause thus far has defied explanation. It was concluded that a more formal investigation of the
malady was fully justified and of high priority. The urgency of such investigation was emphasized further
by our past experience with the American chestnut and American elm. Through the efforts of
Representative Barrus, the State legislature in 1963 appropriated a sum of $25,000 specifically
earmarked to aid the University in initiating a program of research into the cause and possible cure of
sugar maple decline. In 1964, an additional $30,000 was similarly appropriated. Federal funds for
research in forestry have been made available also to supplement the state appropriations.
Although the legislature had been generally appreciative of the value of the sugar maple to the
Commonwealth, it was necessary for Representative Barrus to point out its inestimable worth as a
shade tree and its vital contribution to the beauty of our landscape. Monetary values for timber can be
estimated much easier than such values for aesthetics. There are approximately 170 million board feet
of sugar maple lumber in standing sawtimber throughout Massachusetts and perhaps an additional 115
million cubic feet of wood in trees of less than sawtimber size. Furthermore, there are estimated to be
12 million sugar maple trees in the State large enough to be tapped for maple syrup. All told, the sugar
maple tree in Massachusetts provides the raw materials (wood and sap) which are the base for a several
million dollar contribution to the State's gross annual product.
Exploratory investigations of sugar maple decline in several states including Massachusetts, New York,
Vermont, New Hampshire, Pennsylvania, Michigan, and Wisconsin amply demonstrate the obscurity and
probable complexity of the cause of this malady. As a result, it was decided at the University of
Massachusetts to establish a research team that could attack the problem simultaneously through a
variety of approaches. This team includes three pathologists, (Drs. Walter M. Banfield, Francis W.
Holmes and Malcolm A. McKenzie), a virologist (Dr. George N. Agrios), a nematologist (Dr. Richard A.
Rohde), an entomologist (Dr. William B. Becker), and three soil scientists (Drs. John H. Baker, Donald L.
Mader, and Louis F. Michelson), with a physiologist (Dr. Arthur H. Westing) as project leader. The team is
assisted by four graduate students and from time to time, as necessary, by various other members of
the University faculty. Much credit is due those members of the Berkshire Pioneer Maple Producers'
Cooperative who have graciously made their properties available to the research team for field
investigative work.
Before closing it may be of value to describe briefly the symptoms of sugar maple decline. Affected trees
are characterized by undersized, chlorotic (yellowish), and sparse foliage. The leaves exhibit early
coloration and fall prematurely. Twigs and branches of the upper crown die. Three is a reduction in rate
of growth. Some of the trees die over a period of three to four years, but others seem to have arrested
their decline and some may be recovering. The decline is more apt to occur in old trees than young and
is particularly prevalent in trees that have in one way or another been disturbed by man. The decline
does not appear to spread from one tree to another. It is noteworthy that several other hardwood
species have in recent years also been showing greater or lesser degrees of decline.
We should greatly appreciate learning whether and to what extent the sugar maples in your area are
similarly afflicted. Any additional information or comments you may have on the subject would, of
course, be most welcome.
Global Warming
Cause Of Maple Dieback Takes New Tack - Research points finger at global warming
Research
Maple Syrup Digest
Vol. 2A, No. 2
June 1990
REF# 204
Just when everyone is getting comfortable with the ideal that acid rain is guilty of killing our maples,
here comes a scientist who claims that global warming could be the main culprit.
Dr. Allan Auclair, a scientist with Forestry Canada's Laurentian Forestry Centre in Ste. Foy, Que., doesn't
dismiss acid rain as a contributing cause of dieback, but his theory suggests that global warming may
present the big picture.
Typically, dieback begins with the leaves turning colour early and failing in August. As the disease
continues, twigs and branches of increasing size, particularly in the crown of the tree, begin to die. The
question is, why?
When he presented this theory at a recent conference of the International Union of Forestry Research
Organization (IUFRO) Dr. Auclair said that the earth's warmer mean temperature leads to greater
extremes of weather which can harm trees periodically. He explained that during a prolonged mid-
winter thaw the sap rises early; a subsequent and sudden hard freeze can cause permanent damage to
the trunk.
The trunk moves water to the crown, but if it is damaged by such a freeze-up, the tree in effect is
strangled. Its roots start dying, disease-causing agents ultimately attack the tree and cause its death.
Dr Auclair developed his theory by analyzing reports on dieback prepared by the Canadian departments
of the Environment and Agriculture and 100 years of northern hemisphere data on mean temperatures.
The latter show that since 1880 the temperature has risen an average of .6°C or almost 1.2°F.
Temperature Change Has Whiplash Effect
There have been three major outbreaks of dieback on hardwoods in Quebec during this century alone:
black ash in 1927, yellow birch in 1937 and sugar maple in 1981. Dr. Auclair found that in all three
instances the winters were highly unusual with extended mild spells followed by periods of intense cold.
"The coincidence was remarkable," he said.
Other scientists and industry experts aren't so sure that global warming is the cause. They claim
numerous factors may be at play. Some blame acid rain, others a combination of acid rain and global
warming. One thing is certain: it's not a simple problem. Compounding this is the fact that some
research indicates that the last five years have been the warmest this century.
Sugar maple dieback was most recently noted by foresters and maple-syrup producers in the Eastern
Townships of Quebec following the winter of 1980-81.
By the end of the decade, half of Quebec's sugar maple had been affected by dieback and fifteen
percent had already died. White ash, beech, linden, yellow birch and red maple are also in danger.
Furthermore, fir, white spruce and hemlock are showing signs of dieback too.
New Findings To Be Unveiled In August
Dr. Auclair will present two new research papers on the impact of global warming on dieback during
IUFRO's XIXth World Congress in Montreal next August. The issue has attracted the interest of many of
IUFRO's 15,000 members in 105 countries.
"It's important to realize that acid rain and global warming aren't the same thing," said Dr. Auclair. "A
simple distinction is that acid-rain gases, which are different from the greenhouse gases, have impact on
a region, while greenhouse gases have an impact on the globe."
Not only does dieback occur globally - in Europe it has affected as least 8,000,000 hectares of forest - it
is also found in regions with little or no acid rain, such as the south-east coast of Alaska. This lends
support to a climate- based theory says Dr. Auclair.
By the end of the decade, half of Quebec's sugar maple had been affected by dieback and fifteen
percent had already died. White ash, beech, linden, yellow birch and red maple are also in danger.
Furthermore, fir, white spruce and hemlock are showing signs of dieback too.
Acid rain contains sulfuric and nitric acids which are given off by burning coal, oil and gas, a process that
is also responsible for global warming, or the greenhouse effect, through the release of carbon dioxide.
This gas, called CO2 along with chlorinated fluorocarbons, methane, nitrogen oxide and ozone, inhibits
the natural release of heat from the earth's atmosphere, and the earth gets warmer.
Since the middle of the XIXth century, carbon dioxide levels have increased by as much 25%. Some
scientists predict that the world temperature or temperatures could rise by another centigrade degree
before the end of the millennium. Most climatologists agree that global warming will certainly increase.
Fourteen Contributing Factors
Most experts, including Clarence Coons, Agroforestry coordinator for the Ontario Ministry of
Agriculture, in Kemptville, agree that there is no consensus as to the cause or possible cures of dieback.
Mr. Coons, a respected sugar-maple expert, says scientists and industry experts do not know whether
man-made influences are causing dieback to occur more frequently and they cannot decide what can be
done to control it.
He suggests that fourteen possible factors are contributing to maple decline: aging trees, root, stem and
branch defects, drought, insect damage, restricted rooting depth, excessive exposure from blowdown
and thinning, winter injury, mechanical damage to bark resulting in decay, overstocking, grazing by
livestock, marginal sites, low soil fertility, improper tapping and air pollution.
"Some believe that maple decline is caused by acid rain or climate change, for example," says Mr. Coons.
I believe that tree health problems often develop in woodlands because of the lack of appropriate action
or of forest mismanagement many years previous."
According to him, the forest is one of nature's most complex ecosystems and little is actually known
about its natural workings. Even less is known about a forest in a state of stress.
Accumulation Of Small Stresses Weakens Natural Resistance
"Trees, like people, suffer from stress," says Mr. Coons. "Too much of it can reduce their vigour and rate
of growth, their value as well as shorten their life span. The textbooks say that sugar maple may live for
300 years . . . Most don't."
"The fact is," he says, the health and longevity of trees are influenced by a great variety of biological and
environmental factors which combine to produce conditions either favourable or unfavourable for their
survival. Because trees cannot move to escape adverse conditions, these factors are clearly linked and
easily combine to produce unfavourable conditions which can lead to maple decline."
The widespread presence of dieback is cause for concern in a country where forestry is the largest
industry. Canadian forestry accounts for $17 billion of net exports annually and employs 300,000
Canadians directly and 5,00,000 indirectly.
More specifically, the sugar maple, unique to North America, is the source of maple syrup and other
valuable maple products which are gaining popularity every year. The 1988 Canadian crop was valued at
$98 million, up from $58 million in 1987 Statistics.
Canada figures show that 93 percent of Canadian maple syrup comes from Quebec, the world's maple
syrup leader.