Chapter
17
Plant
Pathology
Offical
TMG
Instructor
Copy
Learning Objectives
1. Explain the basics concepts
of plant pathology
2. Explain why disease occurs and
the various causing factors
3. Identity different symptoms
and signs of diseases
4. Describe the different
types of plant disease
5. Explain the difference between
abiotic and biotic diseases
Plant Pathology
P
lant pathology is the study of the cause
and control of plant diseases. Therefore,
it requires that gardeners have knowledge of plants, the environment, pathogens
and even genetics. Plant diseases are significant because they can cause a reduction in
the quantity and the quality of food, fiber
and timber. Plant diseases can also reduce the
aesthetic value of ornamental plants and the
property values that they afford. The cost to
control plant diseases and the cost of re-planting ruined plants adds to the economic losses
of gardeners.
Plant pathogens are constantly changing
and mutating, resulting in new strains and
new challenges to gardeners and consumers.
Throughout our history, scientists have been
investigating and developing solutions for
controlling devastating disease problems. It
was the disease of grains, cereals and legumes
that lead to the development of the first compound microscope in 1675. The first fungicide
was developed to save the vine industry in
France from downy mildew. It was a mixture
of copper sulphate and hydrated lime called
Bordeaux.
Plant pathogens are hard to identify
because they are so small. This makes accurate diagnosis and positive identification of a
pathogen in the field difficult. In fact, specialized equipment is often required. Therefore, it
is important to teach gardeners how to take a
diagnostic sample from a landscape and submit
it using the county Extension office resources.
Infamous Plant
Diseases
Throughout history there have been numerous human sufferings caused by plant diseases.
Some of the more significant of these include
the Irish Potato Famine, the destruction of the
American chestnut, the destruction of Dutch
elm trees and the destruction of flowering
dogwoods.
The Irish Potato Famine was caused by late
blight. For several years in the mid-1800s, this
disease caused the failure of potato crops in
Ireland. Because potatoes were a staple crop
and the economy was weak, this caused over 1
Tennessee Master Gardener Handbook
476
million people to die and 2 million to immigrate to other countries. For this reason, many
Americans today have Irish heritage.
The American chestnut was a valuable
tree that provided wood for building, food
for wildlife and an article of trade for most of
the Eastern United States. However, chestnut
blight, an imported fungal canker disease,
destroyed the American chestnut by the 1950s.
Fortunately, the American Chestnut Foundation, The University of Tennessee and the U.S.
Forest Service have been breeding, planting
and monitoring hundreds of re-introduced
chestnut trees to search for blight-resistance in
Tennessee, Virginia and North Carolina. The
re-establishment of the American chestnut
species to the Appalachian forests will contribute to building the health and diversity of our
native forest system.
Dutch elm disease was discovered in
Europe in 1910 and was identified in Ohio in
1929, possibly resulting from European furniture exports. This disease has killed over 40
million trees worldwide. Dutch elm disease is
a vascular, fungal disease that is spread by the
elm bark beetles. Fortunately, researchers have
developed injectable fungicides for infected
trees and there are at least 10 disease resistant
cultivars of the American elm (Ulnus Americana). The significance of imported diseases
has lead to the development of the USDA
division of APHIS-Animal and Plant Health
Inspection Service. This agency is charged
with preserving and protecting the health and
value of agriculture and natural resources in
the United States.
Finally, dogwood anthracnose, a vascular
fungal disease, affects flowering dogwoods.
Flowering dogwoods are popular trees in Tennessee landscapes and are worth $100 million
dollars in wholesale to the American nursery
industry. In addition, the flowering dogwood
provides essential vitamins to wildlife in
its berries and foliage. However, dogwood
anthracnose is destroying Appalachian forests,
where the tree has nearly disappeared. Fortunately, there is some hope of curbing this
disease. The University of Tennessee Institute
of Agriculture researchers have been successful
in breading cultivars that have shown positive
Figure 1.
Plant Disease Triangle
Illustrates the 3 Factors
Influencing the Development of a Disease:
Host Plant, Pathogen,
and Environment
disease resistance. One such cultivar is ‘Appalachian Spring.’
What Is a Plant Disease?
Many plant pathologists consider any abnormal condition or plant function to be a disease.
Diseases are described according to the area
of the plant affected by the disease agent. The
categories of pathogens are: foliar, including
the fruit, leaves and stems; root and crown;
and vascular, or wilt, diseases. Foliar diseases
are often associated with spots, lesions, mottling and yellowing. Crown and root diseases
typically reduce the normal functions of the
plant because they cause the inability of the
Figure 2.
Common Plant Functions
Inhibited by Common
Types of Plant Diseases
Tennessee Master Gardener Handbook
477
Table 1. Common Symptoms Description of Plant Disease
Symptom
Description
Blight
General or rapid browning and death of foliage
Butt rot
Rot found at the base of trunk
Canker lesion
Occurs on a stem, branch or twig; canker is often sunken, cracked
and brown
Chlorosis or yellowing
Yellow/green foliage due to the destruction, or lack of, chlorophyll
Die-back
Foliage death begins at the tips of the youngest growth; dying
tissue spreads down into the older foliage
Flagging
Scattered or isolated, dead or dying limbs
Gall
A swelling of plant tissue that may be caused by a bacterial or
fungal infection. It can also be caused by insect or mite activities
(i.e. crown gall)
Mosaic
Chlorotic pattern, ringspots and mottles on leaves, petals or fruit;
associated with virus infections
Mummy
Shriveled desiccated fruit
Necrosis
Dead tissue
Overdevelopment
Plants/plant parts are larger than normal, or certain plant
characteristics are excessive
Root-knot
Irregularly shaped root galls which form as a result of root infection
by Meliodogyne sp. nematodes
Rot
Abnormal softening, disintegration and browning of succulent,
non-woody plant tissue (i.e. root rot)
Spot
Lesion with definite, regular or irregular margins; may be circular,
angular or irregular in shape
Ringspots
Distinct yellow, brown or black rings on otherwise green foliage.
These rings may appear on leaves, fruits or stems
Stunting
Abnormal reduction of plant growth
Underdevelopment
Includes those abnormalities where plant/plant parts are smaller
than normal, or where other plant characteristics are deficient
Witches’ broom
Broom-like growth of plants which occurs as a result of abnormal
branching patterns
Adapted from Agrios 1997, pp254-255 and Trigiano, Windahm and Windham, 2004 p9
plant to absorb water, air and nutrients. Wilt
diseases cause obstructions in the vascular
system, resulting in water and nutrients being
blocked from translocating throughout the
plants.
For disease symptoms to occur, three factors must be present: a susceptible plant, the
presence of a disease agent and an environment favorable for disease development. If one
of these factors is not present, then a disease
cannot develop. However, any practice that
favors plant growth and reduces the amount
of pathogen or its development will lessen the
affect of the disease.
Tennessee Master Gardener Handbook
478
Abiotic Disease
Plant diseases are classified into two major
categories: abiotic, meaning non-living, and
biotic, meaning living. Abiotic, or non-infectious, disease problems include damage from
air pollution, nutrient or water imbalance,
extreme temperatures, low or excessive light,
and chemical or mechanical injury.
Air Pollution Damage
Plants can be early indicators of poor air quality, with some species being more susceptible
to certain pollutants than others. Therefore,
plant injury is usually most common near large
cities, factories, highways, airports and any
refinery or fuel burning industry. Factors such
Table 2. Descriptions of Nutrient Deficiency and Excess Disorders
Nutrient
Deficiency
Excess
Rapid growth, dark green color
and increased yield. Helps with
the building of proteins and
amino acids.
Light green to yellow
appearance of leavesespecially the older leaves,
stunted growth and poor fruit
development.
Dark green foliage that may
be susceptible to lodging,
drought, disease and insect
invasion. Excessive vegetative
growth, falling over and poor
flowering and fruit set. Fruit
and seed crops may fail to
yield.
Rapid growth, stimulates
blooming, and root growth.
Difficult to detect in most
plants. Results in stunted,
darker blue-green or purplish
plants. Dead areas may
develop on the leaves, fruits
and stems. Older leaves are
affected before younger ones.
Excess phosphorus may cause
micronutrient deficiencies,
especially iron or zinc.
Excessive phosphorus in
surface waters can promote
growth of aquatic vegetation.
Potassium (K)
Photosynthesis, plant
metabolism, fruit formation
and winter hardiness.
Decline in growth, poorly
developed root systems and
weak stalks. Older leaves
turn yellow initially around
margins and die. Irregular fruit
development.
Competes with magnesium
and calcium for plant uptake
and causes “salt” injury.
Calcium (Ca)
Cell wall structure, leaf
and root growth vigor and
corrects/neutralizes pH.
Reduced growth or death of
growing tips (roots, shoots);
black and rotted roots,
jelly-like leaf tips. Poor fruit
development and production.
Excess calcium may cause
a deficiency in either
magnesium or potassium.
Chlorophyll manufacturing,
regulates the uptake of
nutrients and accelerates
germination and maturity.
Initial yellowing of older leaves
between leaf veins-mottling
and chlorosis- spreading to
younger leaves; poor fruit
development and production.
Tips and the edges of leaves
may turn upward.
High concentration tolerated
in plant; however, imbalance
with calcium and potassium
may reduce growth.
Sulfur (S)
Dark green color, root growth
and seed production.
Initial yellowing of young
leaves spreading to whole
plant; similar symptoms to
nitrogen deficiency, but occurs
on new growth.
Excess of sulfur may cause
premature dropping of leaves.
Boron (B)
Quality and yield of root crops
and seed production.
Death of growing points,
deformation of leaves with
areas of discoloration and
stunted plants.
Leaf tips become yellow
followed by necrosis. Leaves
get a scorched appearance and
later fall off.
Chlorine (Cl)
Plant metabolism.
Difficult to detect.
Foliar and root burn.
Iron (Fe)
Chlorophyll manufacturing
and a respiratory enzyme.
Chlorotic tissue between the
veins of new leaves leading to
spots of dead leaf tissue. Most
common on azaleas, camellias,
gardenias, blueberries and
centipede turf.
Possible bronzing of leaves
with tiny brown spots.
Manganese (Mn)
Photosynthesis and enzyme
control.
Interveinal yellowing or
Older leaves have brown spots
mottling of young leaves.
surrounded by a chlorotic
Induced by high soil pH (above
circle or zone.
7.0).
Nitrogen (N)
Phosphorus (P)
Magnesium (Mg)
Purpose
Tennessee Master Gardener Handbook
479
Table 2. Descriptions of Nutrient Deficiency and Excess Disorders
Nutrient
Purpose
Deficiency
Excess
Molybdenum (Mo)
Utilization of nitrogen.
Rare, looks like nitrogen
deficiency. Liming will usually
correct a deficiency.
Rare.
Zinc (Zn)
Growth, chlorophyll
manufacturing, enzyme
reactions and synthesis of
auxin.
Interveinal yellowing of young
leaves and reduced leaf size.
Deficiencies usually on sandy
soils with a pH above 6.5 in
the early spring or on soils that
have recently been limed.
Excess zinc may cause iron
deficiency in some plants.
Fluoride (F-)
Water treatment for human
health.
None.
Foliar burn in tropical plants,
and houseplants.
as concentration of pollutant, type of pollutant, species affected, distance from source,
length of exposure and climate may magnify
or extend damage. Different pollutants cause a
variety of damage to plants. Most commonly,
the damage includes: the collapse of leaf tissue,
the yellowing or color change, alterations in
growth or premature loss of foliage. There are
numerous types of air pollution. Some of the
most common ones are described below.
▪▪ Sulfur Dioxide: Blotches on leaf or
marginal and interveinal necrosis.
▪▪ Fluorides: Scorching or tip burn
exhibited as yellowish mottle and
marginal chlorosis, tip necrosis chlorosis of evergreens.
▪▪ Chlorine: Bleached or brown areas at the tips of the leaves may
have streaking along veins.
▪▪ Ozone: Most commonly diagnosed, tissue death, stunted growth,
marginal scorch and leaf roll.
▪▪ Ethylene: Commonly associated with
ozone damage. Ethylene is a natural
plant growth hormone or regulator that affects developing tissues.
One symptom is call epinasty, which
is the curling of leaves and shoots.
Lime
Lime is added to the soil to adjust the acidity of the soil to bring
it to the ideal pH of 6.0 to 7.0. At this level, nutrients become readily available to plants, increase the microbial population in the soil,
and nitrogen and sulfur are converted to available forms.
Tennessee Master Gardener Handbook
480
Nutrient Disorders
As explained in the Soil chapter, plants require
several mineral elements for normal growth.
Symptoms produced by deficiencies of certain
elements are dependent on the plant and the
reason for the deficiency. Because nutrients are
taken up in a water solution through cationic
exchange, the surplus of one nutrient may
block another nutrient from an exchange site.
Therefore, nutrients are taken up in excess,
creating a deficiency of other elements. Soil
and water containing high concentrations of a
mineral may be toxic and have injurious effects
on a plant.
Injury on plants varies in severity depending on many different factors including: age
of plant, sensitivity of species, pH of the
soils, temperature and other minerals, or
“salt,” concentrations. To avoid most nutrient
problems, soil should be properly cared for and
water should be tested for excess minerals (see
Chapter 3, Soils).
Water Damage
Inadequate or excessive watering can cause
wilting, dieback, scorching, leaf drop and
discoloration. The symptoms of over-watering
and drought look similar. This is because when
the root system is deprived of water or oxygen,
the plant will not be able to circulate water
and nutrients throughout the plant’s system.
Subsequently, nutritional deficiencies may occur. For more information on plant/water/soil
relationships, please see Chapter 3, Soils and
Chapter 4, Water.
High or Low Temperatures
In some plants, the cells inside the leaves and
stems freeze. The cell’s water freezes causing
the cell membranes to rupture, killing that
part of the plant tissue, but not necessarily the
whole plant. This rupture of cell membranes
results in water-soaked lesions, necrosis or a
sun-scorched look. Freeze damage in some
plants may cause wilt, where water escaped
from plant cells too quickly due to a rapid drop
in temperature. In this case, cells in the plant
actually deflate, causing the tissue to wilt. This
is known as epinasty.
After a late spring freeze, flowers and
tender buds may be lost on plants that flower
on old growth, such as some hydrangeas and
Table 3. Herbicide Groups and Description of Injury
Herbicide Group
Description of Injury
Post-emergence broadleaf
herbicides
Twisted leaves
Prone to drift and volatilization
Downward cupping of leaves
Narrow, strap-like leaves on the
youngest growth
Aboveground roots on the stems
Grass Herbicides
Yellowing, and bleaching
Dieback in actively growing regions
of ornamental grasses
Non-selective broad spectrum
herbicides
Yellowing of foliage
Dieback and eventually death
Figure 3. Freeze Damage (11 degrees F) an Abiotic Disease
A. Daylily
B. Oakleaf
Hydrangea
C.Hosta
D.Boxwood
climbing roses. However, plants that bloom on
new growth, such as crape myrtle and butterfly
bush, may still bloom after they have recovered
from freeze damage. Because of the dangers
of freeze damage, inform gardeners to protect
the crown and roots of plants sensitive to cold
temperatures.
During a typical summer in Tennessee,
temperatures can get into, and in excess of,
90 degrees. Some plants can tolerate excessive
heat for a few days, but extended periods of
heat can cause abnormal biochemical reactions that result in slowed or abnormal growth.
Water-loss is also a factor during times of
excessive heat. Water is lost through stomata
during evapotranspiration as the plant finds a
balance for transpiration. Symptoms are similar to inadequate watering.
Chemical Damage
Chemical drift to non-target plants can cause
unusual growth, discoloration, spotting and
death. Accurately diagnosing a chemical injury
can be difficult, especially if it is unknown
what chemical has been applied. Improper
applications of herbicides, fungicides, insecticides, fertilizers and growth stimulants can
all result in chemical damages. Therefore, it is
important to always teach gardeners to follow
the label instructions and apply products during the appropriate weather conditions to avoid
wind drift and runoff.
The most common chemical injury is from
herbicides. Herbicide injury can resemble
insect/mite damage, drought, soil compaction, root stress and other issues. Usually an
Extension professional can examine a plant to
determine the probability of herbicide damage
and group of chemical.
Other Environmental and
Mechanical Damage
Nature can be detrimental to plants. Wind,
ice or snow can all cause breakage or tears in
plants making them more susceptible to infectious diseases. Excessive winds can also dry or
split plant tissues. Lighting can burn, tear or
kill plant or tree tissue.
A host of other improper agricultural, horticulture and construction practices can cause
damage to plants and lead to significant loses
in the landscape. In urban areas, new site construction can lead to poor soil conditions and
Tennessee Master Gardener Handbook
481
root damage. Extreme excavation can change
the water table. Teach gardeners to avoid
injuring plants with machinery, lawn mowers
and trimmers. Also, teach them to never nail
or wrap fencing to a living tree, this will cause
the trunk to girdle. Mechanical injuries cause
by nature or man can create entries or stresses
for infectious disease to enter the plant.
Biotic Disease
Biotic, or infectious, disease problems are
caused by living, (usually) microscopic organisms in a sustained relationship or by pests,
insects or other animals that feed on, or
otherwise damage, plants. Biotic diseases often
require vectors to carry the disease from plant
to plant. The most common vectors are: wind,
water, insect and mechanical contacts - infected and unclean tools. The different types of
biotic disease agents include parasites; saprophytes, bacteria or fungi; nematodes; mycoplasmas, viroids and viruses. Each is discussed
in more detail below.
Figure 4.
Life Cycle of Monilinia Fructicola, a Fungus that Causes
Brown Rot of Peach
Tennessee Master Gardener Handbook
482
Fungi
Fungi are small, usually microscopic, plants.
They differ from high plants because they
do not contain the green pigment, known as
chlorophyll. Most fungi obtain nourishment
from dead plants and dead animals. These are
beneficial fungi. However, there are about
8,000 species of fungi that cause disease in
plants. Eighty percent of all plant diseases are
because of these fungi.
The life cycle of a fungus usually involves
time with the host plant and time in the soil,
or on plant debris in the soil. The survival of
the fungus depends upon temperature and
moisture. In order to control a disease problem, the disease agent’s life cycle and the manner in which the disease agents spread from
one plant to another must be known. Wind,
water, birds, insects, mites, other animals, man
or soil can distribute fungi.
Bacteria
Bacteria are microscopic organisms existing
as single cells or short chains of cells. Most
obtain nourishment from dead plants and
animals. These are known as decay bacteria.
However, there are about 200 species of bacteria that cause diseases in plants.
Bacterial diseases spread from one plant
to another by water droplet splash, wind and
insects. Because bacteria develop in water
droplets on seeds and young seedlings, dry
conditions can slow the spread and development of bacterial diseases. However, even in
dry seasons, gardeners need to be cautious
when planting varieties susceptible to bacterial
infection because some bacteria can overwinter
in decaying crop debris, the cankers of woody
plants or on seeds.
Bacteria enter susceptible plant tissues
through wounds or natural openings. Generally, young tissues are more susceptible to
pathogenic bacteria than older tissues. The
development of the disease depends on many
factors including: the maturity of the tissue,
the susceptibility of the tissue, the optimum
temperatures, the humidity needed for disease
development and the particular bacterial species involved.
Symptoms of a bacteria infection include
leaf spots, leaf blight, cankers and wilt diseases. Leaf spot/blight bacteria typically enter
the leaves and multiply. Sometimes, these
bacteria multiply and develop in the plant
until the whole plant is dead. Other times,
these bacteria may be restricted to small areas
or spots. Wilt bacteria first develops in plant
roots. Once in the roots, the bacteria multiply
and spread up into the xylem. As a result, the
foliage does not receive adequate water and
wilting results. Usually plant death follows
quickly. Because wilt bacteria are soil-borne,
they can remain in the soil for a long period of
time - 6 to 8 years. Therefore, gardeners must
take care not to grow plants varieties susceptible to wilt bacteria in that same area.
Viruses
Viruses are sub-microscopic structures that can
only be viewed with an electron microscope at
a magnification of 100,000 - 200,000. Viruses
cannot live in the absence of a larger, more
complex living organism; they even reproduce
inside plant or animal cells. To date, about
1,000 viruses have been described. Half of
these viruses cause plant diseases. Plant virus
classification is based on the most common
symptom caused on the first host where identification was made. Hence, tobacco mosaic
virus (TMV) was first identified as a mosaic
type of disease on tobacco.
Figure 5.
Life Cycle of Erwinia Amylovora, Cause of Fireblight on Apple.
Typical symptoms of fireblight: Flagging dead limb with a shepherds
crook at the end of the branch.
In the spring, insects such as aphids, thrips
and leafhoppers pick-up viruses from overwintering plants and weeds. After an incubation
period, the insect transmits the virus to other
plants during feeding. The period of time that
an insect is able to transmit a virus depends on
the virus and the insect. In addition to insects,
viruses can be transmitted by vegetative propagation or by mechanical transmission through
sap, seed, pollen, mites, nematodes, dodder or
fungi.
Once transmitted to the plant, the virus
enters the plant through wounds. Once in
the plant, the virus acts as a nucleus, directing the cells’ activity toward replication of the
virus. Once a cell is filled with virus particles,
these particles move from one cell to another.
Eventually, the virus particles move through
the phloem or xylem so that the whole plant is
infected. Once the plant is infected, symptoms
appear usually in 3 to 14 days, depending on
the plant, virus and environmental conditions.
However, some virus diseases may not show
symptoms for a much longer time period after
infection takes place.
Other Disease Causing
Organisms
Other organisms that can cause disease are
mycoplasms, viroids, parasitic higher plants
and nematodes. Mycoplasms are about the size
of large viruses and must be studied with an
electron microscope. Mycoplasms differ from
bacteria in their smaller size, their lack of a
cell wall and their lack of a nuclear membrane.
Mycoplasms generally cause: yellowing and
stunting of leaves, stunting of the entire plant,
proliferation of shoots (witches’-brooms),
abnormally green and/or sterile flowers, and
the decline and death of plants. Most mycoplasms are transmitted from plant to plant by
leafhoppers.
Some viral diseases are caused by unusually
small, nucleic acid particles that do not contain
the protein covering typical of virus particles.
These atypical viruses are called viroids. The
disease characteristics of viroids are similar to
those of viruses.
There are only a few parasitic higher
plants that cause diseases of cultivated plants.
These plants include mistletoes, dodder and
witchweed. These cause disease by removing
nutrients and water from the host or suscepTennessee Master Gardener Handbook
483
tible plant. They may cause a reduction in plant
growth.
Nematodes can also cause disease in plants.
There are about 12 different genera of plant
parasitic nematodes in the Southeast that are
responsible for economic losses. Plant parasitic
nematodes are only about 1/64 to 1/25 of an
inch long. They have a spear-shaped feeding structure located in the head region that
enables them to puncture plant tissue and feed.
Most plant parasitic nematodes live in the soil
and feed on roots. However, a few migrate up
the plants and feed on the foliage.
The life cycle of a plant parasitic nematode
consists of the egg, four larval stages and the
adult stage. Nematode diseases are spread by
soil clinging to machinery, shoes, transplants
or other plant material. The survival of nematodes depends on temperature, moisture, type
of nematode, presence or absence of a living
host plant and the stage in the life cycle when
adverse conditions occur.
Above ground symptoms of nematode
damage include stunting, yellowing, uneven
growth, wilting and plant death. However,
these symptoms can easily be confused with
acid soils, low fertility, poor drainage, soil
compaction and root disease. Below ground
symptoms of nematode damage include knots,
or swelling on roots; lesions, or dead areas, on
roots; stubby roots; dead roots; restricted root
system; or a lack of feeder roots. Symptoms
usually occur in irregular spots in the field or
in planting.
Disease Management
Disease management generally refers to the
control of the development of disease in a field,
garden or landscape. Without addressing the
disease as it develops, gardeners risk losing all
of their plants. For disease control in the home
garden, the most common recommendations
include sanitation; cultural, or environmental,
modifications; chemical application and the
use of resistant varieties. The specific recommendation depends upon: the disease agent,
the plants affected, the size of planting, the
Chemical Controls
Before using a chemical control, the pesticide should be referenced in the Tennessee Pest Control Handbook (check name a publication number) for making all pesticide recommendations.
Tennessee Master Gardener Handbook
484
Measuring Fungicides
Spoonful measures for fungicides are
level, not heaping.
age of planting, the severity of the problem
and the availability of fungicides and resistant
varieties. Root diseases and vascular diseases
usually require sanitation, crop rotation and/
or the use of resistant varieties or fumigation.
Foliar diseases typically require sanitation and/
or chemical treatment, and sometimes other
cultural modifications. For more information
on disease management, please see Chapter
21, IPM and Chapter 22, Understanding
Pesticides.
Crop Rotation
Crop rotation is often the most practical
method of disease control for some soilborne bacterial and fungal and nematode disease problems. Recent research
has shown that certain plants, besides
being revenue-generating crops, also
have a suppressive effect on diseases. For
example, after broccoli and other crucifer crops are harvested and the plant residue is plowed into the soil, the decomposition of the broccoli stems and leaves
releases natural chemicals that can significantly reduce the number of Verticillium dahliae microsclerotia. This broccoli
effect can be an important consideration
in crop rotation strategies. Some cover
crops, such as mustards and sudangrass,
might also share this beneficial effect. It
is important to remember that while rotations with non-susceptible plants and
cover crops may help reduce soil-borne
pathogen numbers, significant decreases in such populations are likely to take
many seasons.
Submitting Plant and Insect Samples
The information below is taken from the University of Tennessee Soil and Plant Center website. The web address for
this sight can be found in the Resources section of this chapter.
1. Obtain an Insect and Plant Disease Information Sheet by going on to the University of Tennessee Soil and Plant
Center website or by contacting your local UT Extension office. Please complete the information on the upper
portion of the information sheet and provide as much information as possible for the sample being submitted.
2. Send generous amounts of material for sample. Enclose plant material in plastic bags. Never add water to any
samples, never mix several host (insect) species in a single bag, and avoid loose soil.
3. Send specimens to the Center immediately after collecting. If this is not possible, and a holdover is encountered,
keep specimen(s) cold. Mail packages to arrive on weekdays (Monday thru Friday) rather than during a weekend
or holiday.
4. Protect specimen(s) from being crushed in the mail. Place insects in a vial of alcohol and send them in a mailing
tube.
5. If general decline or dying plants is observed, send whole plants showing early symptoms, with roots and
adjacent soil intact. Dig up carefully. If a field crop has the issue, send several plants. Dead plants are useless for
examination.
6. When it is not possible to send whole plants, always send generous samples of aboveground portions, with early
symptoms showing, at least a pint of soil and a good handful of feeder roots. This especially applies to large ornamentals, shrubbery, evergreens and small trees. Be sure to enclose all materials in plastic bags.
7. When localized infections, such as cankers, leaf spots and rots, are involved, send specimens representing early
and moderate stages of disease. For cankers, include healthy portions from above and below the diseased area.
8. Dead plants, material that is dry or decomposing on arrival, and specimens arriving without necessary information and payment cannot be diagnosed.
9. Send specimen(s), Insect and Plant Disease Information Sheet, and appropriate fees to the Soil, Plant and Pest
Center (see address and fee information on the Insect and Plant Disease Information Sheet). Do not place
information sheet and payment inside the sample bag. Fees can also be paid by credit card using the secure UT
Institute of Agriculture eMarketplace site.
Disease Diagnosis
Disease diagnosis is done by observing plants,
collecting samples and examining samples.
If the problem cannot be diagnosed in the
field, then a sample needs to be collected
and brought into the county Extension agent
as soon as possible. If the county Extension
agent is not able to diagnose the problem in
the office, they may send it to the University
of Tennessee Extension Soil, Plant and Pest
Center in Nashville. At the Soil, Plant and
Pest Center lab, many samples are examined
microscopically for evidence of bacteria or
fungi. For more information on plant diagnostics and on submitting plant and soil samples
please see Chapter 3, Soils and Plant Nutrition
and Chapter 20, Diagnosing Plant Problems.
As explained in the preceding sections,
plant diseases can be caused by many different
factors. However, diseases do cause characteristic symptoms that can aid with the identification of the disease. Therefore, the tables at the
end of this chapter detail many of the common
plant diseases, the symptoms they cause and
the strategies used to manage them.
Summary
Plant pathology is a diverse field of study.
Pathogens can range from microscopic
organisms to something as consuming as air
pollution. The effects of pathogens can be
devastating. Therefore, it is crucial to identify
pathogens and how to treat them, before they
destroy the health of the landscape or garden.
Tennessee Master Gardener Handbook
485
Terms To Know
Anthracnose
Bacterial blight
Bacterial leaf spot
Bitter rot
Black knot
Black rot
Black root rot
Black Spot
Blossom blight
Bot rot
Botryosphaeria canker
Brown rot
Cane blight
Canker
Cedar apple rust
Cedar-hawthorne rust
Cercospora leaf spot
Coccomyces leaf spot
Collar rot
Crown gall
Defoliated
Dogwood anthracnose
Downy mildew
Drench
Edema
Entomosporium leaf spot
Eutypa dieback (Dean arm)
Fabraea (Entomosporium) leaf spot
Fire blight
Fly speck
Foliar blight
Gall
Gray leaf spot
Gray mold
Inoculum
Late leaf rust
Leaf blotch
Leaf galls
Leaf scorch
Leaf spots
Leather rot
Macrophoma leaf spot
Mummy berry
Necrotic tissue
Nematodes
Orange rust
Overwinter
Peach leaf curl
Phoma stem rot
Phomopsis canker
Phomopsis blight
Phyllosticta leaf spot
Powdery mildew
Tennessee Master Gardener Handbook
486
Pustles
Red stele
Rhizosphaera needle cast
Rosette
Rust
Scab
Septoria leaf spot
Sooty blotch
Sphaeropsis dieback, Tip blight
Spot anthracnose
Stem blight
Sterility
Taphrina leaf blister
Tubakia leaf spot
Twig blight
Verticillium wilt
Volutella blight
Volutella canker
White rot
Test Your Knowledge
1. What is the difference between an abiotic
and biotic disease? Give a symptom an
example of each.
2. What are the best ways to decrease disease occurrence in the landscape?
3. Describe the symptoms of fire blight
on crabapple and name one method of
treatment.
4. What is the key to controlling rosette in
blackberry plants?
5. What are the common symptoms of powdery mildew, rust and pythium root rot?
Name a plant that each of these diseases
infects.
Resources
American Phytopathological Society
apsnet.org
The Tennessee Pest Control Handbook
Available at local Extension agent offices
and online at: http://www.utextension.
utk.edu/publications/pests/default.asp
The University of Tennessee Extension
Publication Webpage
utextension.tennessee.edu
The University of Tennessee Soil, Plant Pest
Center
soilplantandpest.utk.edu
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Ash (Fraxinus)
Anthracnose (fungal)
Symptoms: Large brown lesions on leaves and premature leaf
drop. Defoliated branches often produce new leaves by midsummer. White ash is more susceptible to anthracnose than
green ash.
Rake and compost, or destroy, leaves. For valuable
specimen trees that have a history of anthracnose, apply a
fungicide spray when buds begin to open. Repeat at 10 to
14-day intervals.
Azalea (Rhododendron)
Prune out diseased branches. Irrigate and fertilize to
stimulate vigorous growth.
Phomopsis Canker (fungal)
Symptoms: Individual branches wilt and die.
Phytophthora Root Rot (fungal)
Symptoms: Plants may wilt rapidly, even with adequate soil
moisture. Diseased roots are dark reddish-brown. May spread
rapidly in nurseries with poor sanitation. Root rot may be
more severe in poorly drained clay soils.
Buy disease free plants. Plant in well-drained soils. If
planting in areas where water stands or in poorly drained
soils, use raised beds. Soil can be amended with 4 inches of
pine bark to improve drainage. Do not irrigate excessively.
Azalea cultivars resistant to root rot include Rhododendron
yedoense var. poukhanense, Glenn Dale hybrids: Fakir,
Glacier, Merlin and Polar Seas; Back Acre hybrids: Corrine
Murrah and Rachel Cunningham; Pericat hybrids: Hapton
Beauty and Sweetheart Supreme; Satsuki hybrids: Higasa,
Eikan, Shinkigen and Pink Gumpo; Gable hybrid: Rose
Greeley; Rutherfordiana hybrid: Alaska; Kurume hybrid:
Morning Glow; and Carla hybrids: Fred D. Cochran and Jan
Cochran.
Powdery Mildew (fungal)
Symptoms: White powdery spots appear on leaves. The entire
leaf surface may be covered. Deciduous azaleas are most
susceptible.
Spray with fungicide at the first sign of disease. Repeat at 10
to 14-day intervals.
Flower and Leaf Gall (fungal)
Symptoms: Leaves and flowers may develop fleshy pale green,
or whitish, galls.
Remove and destroy galls.
Boxwood (Buxus)
Volutella Canker (fungal)
Symptoms: Plants may develop irregular, brownish and
sometimes concentric lesions on leaves. Brownish cankers
also develop. Plants may wilt and then die.
Remove diseased branches. Apply first fungicide spray after
branch removal in spring; second after new growth is ½
expanded; third after growth is completed; fourth in the fall.
Phytophthora Root Rot (fungal)
Symptoms: Individual or multiple branches may turn yellow
then brown. Roots are discolored and decayed.
Apply fungicide as a drench to containers or beds. Use
enough to saturate the soil mixture. Plant in well-drained
sites and avoid planting in poorly drained clay soils.
Macrophoma Leaf Spot (fungal)
Symptoms: Straw colored leaves are covered with black
fruiting bodies. Symptoms may indicate root or stem injury.
This disease is most visible in the early spring.
This fungus frequently colonizes dead or injured leaves.
No control methods are needed. Remove dead leaves for
aesthetic value.
Tennessee Master Gardener Handbook
487
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Nematodes
Symptoms: Yellowing and bronzing followed by thinning
foliage. Leaf size is reduced, growth is retarded and defoliation
may follow.
Purchase nematode free plants. Irrigate during periods
of drought. Avoid planting in soils infested with lesion
nematodes.
Buckeye (Aesculus)
Anthracnose, Leaf Blotch (fungal)
Symptoms: Large areas of necrotic tissue develop on leaves and
complete defoliation may occur. Blotch is most severe on Ohio
buckeye and common horse chestnut. Red and yellow buckeye
may also be infected.
Spray with fungicide at bud break and at 7 to 14-day intervals
during cool, moist weather. On mature landscape trees, this
disease usually develops after annual growth is complete and
may not influence the tree’s growth.
Cotoneaster
Fire Blight (bacterial)
Symptoms: Leaves and branches turn dark brown to black.
Spray with pesticide at early bloom and repeat at 5- to 7-day
intervals during bloom. Best control is obtained from spraying
at night. Prune out infected branches and disinfect shears
between cuts.
Crabapple (Malus)
Cedar Apple Rust (fungal)
Symptoms: Yellow leaf spots develop on leaves and fruit.
Spray with fungicide as new growth appears and flower
buds open. Repeat three to four times at 7- to 14-day
intervals. See disease resistant cultivars listed under scab
management strategies.
Fire Blight (bacterial)
Symptoms: Young twigs and branches are killed. Disease
foliage turns dark brown with a distinctive “shepherds crook”
at the tip.
Spray with an antibiotic or copper spray when 20 percent
of the blossoms are open and repeat at 5- to 7-day intervals
during bloom; then apply weekly for 5 to 6 weeks. Prune
out diseased branches. Disinfect shears between cuts. See
disease resistant cultivars listed under scab management
strategies.
Powdery Mildew (fungal)
Symptoms: White powdery spots appear on leaves. New
growth may be distorted.
Spray with fungicide when disease first appears and repeat
at 14-day intervals. See disease resistant cultivars listed
under scab management strategies.
Scab (fungal)
Symptoms: Olive-brown lesions develop on leaves and fruit.
Leaves turn yellow and severe defoliation may occur.
Spray with a fungicide at green tip. Repeat four more
times at 7- to 14-day intervals. Disease resistant crabapple
cultivars include Adams, Adirondack, Baskatong, Bob
White, Centurion, David, Donald Wyman, Indian Summer,
Jackii, Jewelberry, Liset, Louisa, Molten Lava, Narragansett,
Ormistion Roy, Prairifire, Professor Sprenger, Sargent,
Sentinel, Silver Moon, Sugar Tyme, Tina,and White Cascade.
Tennessee Master Gardener Handbook
488
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Powdery Mildew (fungal)
Symptoms: White powdery spots appear on leaves. New
growth may be severely distorted.
Spray with fungicide at the first sign of disease. Repeat two
to three times at 10- to 14-day intervals. Resistant cultivars
of crape myrtle include Acoma, Apalachee, Basham’s Party
Pink, Biloixi, Byers Standard Red, Byers Wonderful White,
Caddo, Catawba, Centennial, Centennial Spirit, Cherokee,
Choctaw, Comanche, Fantasy, Glendora White, Hardy
Lavender, Hope, Hopi, Lipan, Miami, Muskogee, Natchez,
Near East, Osage, Pecos, Powhatan, Regal Red, Sarah’s
Favorite, Seminole, Sioux, Tonto, Tuscarora, Tuskegee,
Velma’s Royal Delight, Victor, Wichita, William Toovey and
Yuma.
Sooty Mold (fungal)
Symptoms: Black fungal growth on leaves and stems. Sooty
mold may interfere with photosynthesis by blocking out the
sun.
Sooty mold grows on insect excrement (honeydew)
deposited by aphids or scale insects. Monitor insect
populations and treat insecticide. Check the label for
application frequency.
Dogwood (Cornus)
Spot Anthracnose (fungal)
Symptoms: Small, circular lesions (1/16”) develop on flower
bracts and leaves.
Fungicide should be applied when bracts begin to open,
when bracts have fallen and in the fall when flower buds
have formed. Resistant cultivars of dogwood include Pinea,
Cherokee Princess, First Lady, Spring Time, Fragrant Cloud,
and Purple Glory.
Dogwood Anthracnose (fungal)
Symptoms: Large lesions develop on leaves in the late spring.
Lower branches are killed. Cankers form on trunk that may kill
tree.
Apply fungicide at bud break and repeat at 2-week intervals
in areas with moderate to severe damage throughout
growing season. Remove dead branches. Remove water
sprouts the in fall. Plant trees in sunny areas with good
air movement. Buy trees from reputable nurseries. Do not
remove trees from the wild. Some cultivars of dogwood are
resistant to anthracnose.
Powdery Mildew (fungal)
Symptoms: White powdery leaf spots develop on leaves.
Sometimes, the entire leaf surface may be covered. Leaves
may turn red in response to infection. Young growth may be
distorted.
Spray with fungicide at first sign of disease and repeat two
to three times at 14-day intervals. Cornus florida Cherokee
Brave, and C. kousa Milky Way Select are resistant to mildew.
C. florida X C. kousa crosses, Aurora, Constellation, Galaxy
and Stellar Pink are resistant to powdery mildew.
Dogwood Canker (unknown)
Symptoms: Areas of swollen or sunken cankers develop
on the trunks of affected trees. Cracked bark develops on
cankers.
The cause of dogwood canker is unknown. Control
measures have not been developed. Cornus florida Purple
Glory appears to be highly susceptible. C. kousa is resistant
to canker. Trees with canker are very susceptible to damage
by the dogwood borer.
Euonymus
Powdery Mildew (fungal)
Symptoms: White leaf spots appear on leaves. Sometimes the
entire leaf surface may be covered. Euonymus japonicus and
E. kiautschovicus are very susceptible to mildew.
Spray with fungicide when disease first appears. Repeat two
to three times at 14-day intervals.
Tennessee Master Gardener Handbook
489
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Buy disease free plants. Bacteria can be spread via infected
plants, infested soil, pots, tools, insects and irrigation water.
Do not replant susceptible plants. Galls may be removed by
pruning. Disinfect shears between cuts. Prune when foliage
is dry.
Crown Gall (bacterial)
Symptoms: Tumor-like growths appear on stems or roots.
Young trees or shrubs may be stunted or killed. Older
established plants are rarely killed.
Hawthorne (Crataegus)
Cedar-Hawthorne Rust (fungal)
Symptoms: Orange spots appear on leaves and swollen fruit
and cankers develop on young shoots.
Fire Blight (bacterial)
Symptoms: Infected leaves and shoots turn black. “Shepherd’s
crook” symptoms, when the terminal end of the shoot is
hooked, may also be present.
Spray with fungicide as new growth appears, three to four
times at 7- to 10-day intervals. Crataegus X lavallei appears
to be resistant to cedar hawthorne rust. Crataegus crusgalli
appears to be highly susceptible to cedar hawthorne rust.
Spray with an antibiotic copper fungicide when 20 percent
of blossoms are open and repeat at 5- to 7- day intervals
during bloom. Then apply weekly for 5 to 6 weeks. The
best control is obtained from spraying at night. Prune out
diseased branches. Disinfect shears between cuts.
Holly (Ilex)
Black Root Rot (fungal)
Symptoms: Blue, English and Japanese holly may appear
stunted, yellowed and may die. Roots are dark brown or black
and decayed. Diseased plants are particularly susceptible to
drought stress.
Buy disease free plants. Do not replant with susceptible Ilex
sp.
Leaf Spots (fungal)
Symptoms: Many fungi cause brown spots on leaves. Older
leaves are often affected.
Spray with fungicide at bud break and continue at 7-day
intervals during cool, wet weather.
Ivy, English (Hedera)
Anthracnose (fungal)
Symptoms: Brown leaf spots develop on leaves. Diseased
tissue may fall out of spots. Often found on weakened,
stressed plant material.
Spray foliage with fungicide to protect new growth at 7- day
intervals.
Bacterial Leaf Spot (bacterial)
Symptoms: Irregular, brown, water soaked spots develop on
leaves. Lesions may extend into petioles and cause leaf death.
May be severe under overhead irrigation.
Reduce overhead watering.
Juniper (Juniperus)
Phomopsis Blight (fungal)
Symptoms: Young twings die-back. They change from light
yellow to ash gray as they die.
Tennessee Master Gardener Handbook
490
Spray new growth with fungicide as it appears. Repeat at 7to 10-day intervals until new growth has matured. Resistant
junipers include Juniperus chinensis : Foeninia, Iowa, Keteleeri,
Pfitzeriana Aurea, Robusta, Sargentii, Glauca and Shoosmith;
Juniperus communis : Ashfordii, Auero-spica, Depressa,
Hulkjaerhus, Prostrata Aurea, Repanda, Saxatilis, and ‘Suecica’;
Juniperus sabina : Arcadia, Broadmoor, Knap Hill, Pepin,
Skandia and Von Ehren; Juniperus Virginia: Tripartita.
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Phytophthora Root Rot (fungal)
Symptoms: Needles and branches turn yellow then brown.
Roots are discolored and decayed. Often mistaken for a foliar
blight if the roots are not examined.
Buy disease free plants. Plant in well-drained beds. Do not
irrigate excessively. Use raised beds if planting into poorly
drained soils.
Laurel Mountain (Kalmia)
Cercospora Leaf Spot (fungal)
Symptoms: Circular gray to light brown spots develop on
leaves. Severe infection may retard growth and suppress
flowering.
Spray with fungicide at bud break and repeat at 7- to 14-day
intervals. Remove diseased foliage. Rake and remove fallen
leaves.
Laurel, Cherry or English (Prunus)
Bacterial Leaf Spot (bacterial)
Symptoms: Brown leaf spots develop and tissue falls from
spots forming “shot hole” type symptoms -the centers of the
leaf spots fall out, creating a shot hole effect. Defoliation may
occur.
Spray with fungicide at bud break and repeat at 7- to 14-day
intervals. However, this interval may need to be shortened
during wet weather. Space plants to allow for air movement.
Use drip irrigation if possible. This will help keep foliage dry.
Leucothoe
Cercospora Leaf Spot (fungal)
Symptoms: Gray spots with purple margins. Leaf spots may be
severe, resulting in severe defoliation and death.
For severely diseased plantings, prune out diseased foliage
in late winter/early spring and spray with fungicide at bud
break and at 10 to 14-day intervals during wet weather.
Powdery Mildew (fungal)
Symptoms: White powdery spots appear on leaves. The entire
leaf surface may be covered. Severe infections may cause
stunted growth.
Spray with fungicide at the first sign of disease. Repeat at 10
to 14-day intervals.
Lilac (Syringa)
Bacterial Blight (bacterial)
Resembles fire blight of apples and pears. Young shoots
are killed and blackened. Usually occurs during cool, moist
weather.
Prune out diseased shoots when foliage is dry. Disinfect
shears between cuts. Avoid use of high nitrogen fertilizers.
Powdery Mildew (fungal)
Symptoms: White powdery spots appear on leaves. The entire
leaf may be covered. Often appears in early summer. Most
severe on common and Persian lilac.
Spray with fungicide when disease appears and repeat
at 14-day intervals. Choose lilac with some resistance to
mildew such as: Syringa meyeri; S. microphylla; S. patula
Miss Kim and S. reticulata.
Magnolia
Winter Leaf Burn (weather)
Symptoms: On Magnolia grandiflora leaves may be desiccated
during winter months and exhibit marginal necrosis
(browning). Leaves may also become colonized by a weak
pathogen.
No control measures needed. The new foliage produced in
the following spring should be unaffected.
Powdery Mildew (fungal)
Symptoms: White powdery spots appear on leaves.
Spray with fungicide when disease first appears and repeat
at 14-day intervals.
Tennessee Master Gardener Handbook
491
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Maple (Acer)
Anthracnose (fungal)
Symptoms: Black irregular leaf spots develop on leaves during
wet springs.
Landscape trees are rarely permanently damaged. Rake and
compost leaves.
Phyllosticta Leaf Spot (fungal)
Symptoms: Leaf spots with brown centers and purple
margins. This leaf spot rarely causes premature defoliation.
Common disease of Acer palmatum.
Spray with fungicide at bud break and repeat two to three
times at 7- to 10-day intervals.
Verticillium Wilt (fungal)
Symptoms: One limb, multiple limbs or an entire tree may
wilt and die. Brown discoloration may appear in sapwood.
Symptoms may progress rapidly or slowly over a long period
of time.
Severely infected trees should be cut and removed. As
many roots as possible should be removed. Trees with mild
infections may recover after application of high rates of
a water-soluble fertilizer. Do not replant with susceptible
trees. Resistant trees and shrubs include conifers, katsura,
dogwood, gingko, sweet gum, honey locust, crabapple,
sycamore, oak, pear, birch, hackberry, zelkova, hawthorne,
walnut, willow, mountain ash, boxwood, holly and
mulberry.
Oak (Quercus)
Anthracnose (fungal)
Symptoms: Leaf spots may merge to form large blighted
areas.
Anthracnose - Rake and compost, or destroy, leaves. Spray
with fungicide at bud break and two to three times at 7- to
10-day intervals.
Taphrina Leaf Blister (fungal)
Symptoms: Raised blisters develop on upper leaf surface.
Taphrina Leaf Blister - Spray with fungicide once at bud
swell.
Tubakia Leaf Spot (fungal)
Symptoms: Leaves usually blighted from margin, inward.
Often appears in late summer.
Tubakia Leaf Spot - Rake and compost, or destroy, leaves.
Spray with fungicide at 7- to 10-day intervals.
Powdery Mildew (fungal)
Symptoms: White spots appear on leaves. The entire leaf may
be covered. This is often a late-season disease.
Spray with fungicide when the disease first appears and
repeat at 14-day intervals. No control necessary for late
summer/early fall infections.
Pachysandra
Volutella Blight (fungal)
Symptoms: Large leaf spots and stem lesions develop. Large
areas of beds may be destroyed-especially in plants in the full
sun.
Apply as a heavy fungicide spray or drench. Treat
immediately after disease appears.
Photinia
Entomosporium Leaf Spot (fungal)
Symptoms: Red spots develop on leaves. The spots enlarge
and have brown centers with purple margins. Severe
defoliation may occur. This leaf spot is most common on
Photinia X fraseri.
Buy disease free plants. Spray with fungicide at bud break
and repeat at 7- to 10-day intervals. Prune out severely
infected branches. Rake and remove diseased leaves.
Pine (Pinus)
Tennessee Master Gardener Handbook
492
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Needle Rust (fungal)
Symptoms: Off-white blisters erupt to release orange-yellow
spores before candles expand in the spring. The current year’s
growth is rarely affected.
Sphaeropsis Dieback, Tip Blight (fungal)
Symptoms: Multiple shoots of new growth are blighted during
wet springs. Infected shoots turn yellow, then brown and
then wilt. The current year’s shoots may be stunted and curled
downward.
Fungicide sprays are rarely needed for needle rusts.
Prune out diseased shoots when branches are dry. Spray with
fungicide three to four times, at 10-day intervals, starting prior
to new growth. Do not shear trees during wet weather. Shear
healthy trees prior to diseased trees. Severely infected trees
should be cut and destroyed.
Pyracantha
Fire Blight (bacterial)
Symptoms: Leaves and shoots wilt and then turn brown or
black.
Prune out diseased branches and disinfect shears between
cuts.
Scab (fungal)
Symptoms: Disease closely resembles scab or crabapple. Dark
brown lesions develop on leaves, twigs and fruit. Leaves turn
yellow, then brown and then drop prematurely.
Spray with fungicide at bud break and repeat four times at
7- to 10-day intervals. Pyracantha coccinea hybrids reported
to be resistant to scab and fire blight include Apache,
Fiery Cascade, Mohave, Navaho, Pueblo, Red Elf, Rutgers,
Shawnee and Teton.
Rhododendron
Botryosphaeria Canker (fungal)
Symptoms: Single or multiple branches wilt, turn brown and
die. Occurs most often on plants in landscape beds.
Prune out diseased branches. Spray with fungicide after
any summer pruning. Irrigate during periods of drought.
Rhododendron catawbiense cultivars moderately resistant
to canker include Boursalt, Chinoides White, Cunningham’s
White, English Roseum, Le Bar’s Red, Roseum Two, Sweet
Simplicity and Wissahickon.
Gray Leaf Spot (fungal)
Symptoms: Gray, dead areas develop on margins or tips of
older leaves. Often follows environmental stress.
Fungicide sprays are rarely necessary. Irrigate and fertilize
plants to keep them in a vigorous state of growth.
Leaf Galls (insects or mites)
Symptoms: Leaves develop fleshy, pale green to whitish
galls.
For light infestations, simply remove and destroy galls.
Spray with fungicide just prior to new leaf growth and
afterwards at 7- to 14-day intervals.
Phytophthora Root Rot (fungal)
Symptoms: Plants may wilt rapidly even with adequate soil
moisture. Diseased roots are dark reddish-brown. There are a
limited number of resistant varieties available.
Buy disease free plants. Improve soil drainage and use
raised landscape beds in poorly drained soils. Do not
irrigate excessively. Resistant hybrids include Caroline,
Martha Isaacson, Pink Trumpet, Professor Hugo de Vries,
Red Head. Moderately resistant hybrids include Brickdust,
Broughtonni Aureum, Disca, Dr. A. Blok, Dr. Arnold W. Endtz,
English Roseum, Lucky Strike, Madame Carvalho, Mrs. A.
T. de la Mare, Mr. C. B. Van Nes, Prize, Bosley’s Dexter 1020,
Rocket, Wilbrit and Van Veen.
Rose (Rosa)
Tennessee Master Gardener Handbook
493
Table 4. Descriptions of Common Disease Problems and Management Tactics of Woody Ornamentals
Disease and Description
Management Strategies
Black Spot (fungal)
Symptoms: Dark brown to black spots develop on leaves and
canes. Severe defoliation may occur.
Spray with fungicide at 7- to 10-day intervals starting when
new growth appears. Shorten spray intervals to 5- to 7- days
in wet weather. Rake and destroy diseased leaves. Remove
infected canes. Use drip irrigation.
Rhizosphaera Needle Cast (fungal)
Symptoms: Fuzzy black fungal fruiting bodies appear on green,
1-2 year old needles. Needles turn purple-brown and drop by
late fall. Colorado blue spruce is very susceptible and Norway
spruce is relatively resistant.
Make first fungicide application in the spring when new shoot
growth is ½ to 2 inches in length. Make additional applications
at 3- to 4- week intervals (April - July) until conditions no
longer favor disease development.
Sycamore (Platanus)
Anthracnose (fungal)
Symptoms: Interveinal spots develop on leaves. Shoots may
be killed and cankers may develop on branches.
Spray with fungicide at bud swell and follow with
applications at 10- to 14-day intervals during cool, moist
weather during the spring and early summer. Platanus
X acerifolia (London Planetree) cultivars resistant to
anthracnose include Bloodgood, Columbia and Liberty.
Vinca (Vinca Minor)
Buy disease free plants. Do not irrigate or fertilize
excessively. Spray with fungicide in early spring at 2- week
intervals.
Phoma Stem Rot (fungal)
Symptoms: Infected plants wilt and die. Stems turn black.
Yew (Taxus)
Phytophthora Root Rot (fungal)
Symptoms: Needles turn yellow then rust-red. Roots are
discolored and decayed. Similar symptoms can develop from
overwatering or in waterlogged soils. Yew in waterlogged soils
may develop edema-raised, corky tissue on the underside of
needles.
Tennessee Master Gardener Handbook
494
Do not plant yew in poorly drained soils of high clay
content. Yew is intolerant of flooded, waterlogged soil
conditions.
Table 5. Descriptions of Common Disease Problems and Management Tactics of Common Bedding Plants
Disease and Description
Management Strategies
Common Bedding Plant Diseases
Antracnose Leaf Spot (fungal)
Symptoms: This disease causes sunken, brownish to black
lesions on the bean pods, leaves and stems.
Plant certified seeds and plants and spray fungicides as
appropriate.
Aster Yellow (virus)
Symptoms: This disease causes chlorosis in the leaves, with
the veins remaining green. Leaves may also be small, narrow
and curled. Flowers may also be misshapen with tufts of
deformed leaves. Flowers may also be misshapen.
Control insects-especially leafhoppers, use resistant plants,
remove diseased plants and control weeds.
Botrytis (fungal)
Symptoms: This disease causes brown to black lesions with
grayish spores on above ground plant structures.
Use sanitary practices and apply fungicides as appropriate.
Cercopsora Leaf Spot (fungal)
Symptoms: This disease causes narrow, dark brown leaf spots.
These spots will eventually enlarge and turn into irregularly
shaped lesions with dark tan centers and dark brown to
purple margins. This disease may lead to the yellowing and
withering of infected plants.
Avoid excess irrigation, fertilize with slow release fertilizers
according to the plant’s needs and spray fungicides as
appropriate.
Phytophora Root Rot (fungal)
Symptoms: The seeds and roots are the main sights of
infection. Infected seeds are soft and discolored. Infected
roots are colorless to dark brown and appear water soaked.
Plants are stunted and appear wilted.
Use disease free plants, use sanitary practices and apply
fungicides as appropriate.
Pythium Root Rot (fungal)
Symptoms: See “Phytophora Root Rot.”
See “Phytophora Root Rot.”
Thielaviopsis Root Rot (fungal)
Symptoms: This disease causes plants to appear stunted and
yellow. Roots develop black lesions but do not appear water
soaked.
See “Phytophora Root Rot.”
Tennessee Master Gardener Handbook
495
Table 6. Descriptions of Common Disease Problems and Management Tactics of Fruit Trees
Disease and Description
Management Strategies
Apple Diseases
Apple Scab (fungal)
Symptoms: Velvety, olive-green leaf spots that later become
metallic black and possibly puckered. Leaves fall from the tree.
Fruit have brown, corky lesions and are scabby, deformed and
cracked.
Fungus overwinters on fallen leaves and fruit. Rake up and
destroy them. Follow spray schedule, with emphasis on
early season sprays. Plant scab-immune varieties.
Bitter Rot (fungal)
Symptoms: Small brown spots on the fruit enlarge rapidly,
becoming darkened and almost black. Concentric rings
of spores are sometimes present. The fruit lesion appears
“V-shaped” in a cross-section cut.
Remove mummified fruit, dead wood and fire-blighted
twigs. Follow spray schedule, with emphasis on summer
sprays. Removing newly infected fruit from trees will aid in
control.
Cedar-Apple Rust (fungal)
Symptoms: Small, yellow spots develop on leaves in the
spring. These spots gradually enlarge and turn orange. Later,
black dots appear in the spots on the upper surface and
tube-like protuberances appear on the lower surface. Severe
infection results in heavy defoliation. Fruit lesions appear near
the calyx end and are similar to the leaf lesions.
Overwinters on cedar trees. Removal of nearby cedar trees
lessens the problem, but may not eliminate it. For complete
control, all cedars within 4 to 5 miles would have to be
removed. Spray with a rust fungicide every 2 weeks from
the pink stage of bud development to the third cover spray.
Consider resistant varieties.
Collar Rot (fungal)
Symptoms: Dark coloration of wood at or below the ground
in the root-crown area, sometimes extending up the trunk.
Leaves may be small and yellow in the summer. Symptoms are
the same as for other root problems Isolation of the fungus is
often required for positive diagnosis.
Fungus is soil-borne. Select well-drained soil for planting
and request rootstocks with resistance if collar rot is
anticipated. Avoid the cultivar MM 106.
Fire Blight (bacterial)
Symptoms: Shoots blight from the tip downward. Leaves turn
brown (apple) or black (pear). Shoot tip bends, resembling
a shepherd’s crook. Blossoms wilt suddenly and turn brown.
Limb and trunk blight occur when the infection moves
downward from the infected shoots or fruit spurs into larger
branches on the trunk.
Plant resistant varieties. Avoid excessive nitrogen fertilizer
applications. Cankers and blighted shoots should be pruned
out before the growing season begins. Apply fungicide
every 3 to 5 days during bloom, but not after bloom.
Powdery Mildew (fungal)
Symptoms: On leaves, the fungus appears as whitish, felt-like
patches that spread and engulf the entire leaf. Infected leaves
are narrower than normal, folded and stiff. Infected fruit have
a net-like russeting.
The fungus overwinters on buds infected the previous
summer. Many varieties are resistant. On susceptible
varieties, use a fungicide in the early sprays, beginning at
the tight cluster stage.
Sooty Blotch and Fly Speck (fungal)
Symptoms: Soot blotch appears as superficial, sooty or cloudy
blotches on the surface of the fruit. Fly speck appears on the
fruit as sharply defined, black, shiny dots in groups of a few to
100 or more.
Both fungi overwinter on the twigs of many woody plants.
Apple fruit infections are the most numerous during the
summer. Follow spray schedule and good pruning practices
to allow air, sunlight and spray penetration of the canopy.
Tennessee Master Gardener Handbook
496
Table 6. Descriptions of Common Disease Problems and Management Tactics of Fruit Trees
Disease and Description
Management Strategies
White Rot or Bot Rot (fungal)
Symptoms: Fruit rots show up late but develop rapidly,
beginning as tan or red spots. In cross section, the rot is
cylindrically shaped, extending to the core. The rot may
involve the entire fruit. On green varieties, the rot is tan with
concentric rings. Branch cankers become tan to orange and
papery.
The fungus overwinters in bark and in limb cankers. This
fungus can readily colonize fire-blighted branches. Remove
and destroy all dead branches and twigs. Follow spray
schedule with emphasis on summer sprays. Practice proper
pruning.
Peach and Nectarine Diseases
Brown Rot, Blossom Blight (fungal)
Symptoms: The most noticeable phase is the fruit rot phase.
Small, circular, brown spots enlarge rapidly and become
covered with ash-gray tufts or spores. Fruits shrivel and
mummify. Infected blossoms wilt and turn brown. Shoots can
sometimes become infected and die.
The fungus overwinters in mummified fruit and in cankers.
Remove all mummies and blighted twigs from trees after
last picking. Follow spray schedule with emphasis on the
3-week period prior to harvest. Control insects that injure
the fruit. Keep fruit cool after picking. To lessen the spread
of the disease, remove infected fruits as soon as they are
observed.
Bacterial Spot (bacterial)
Symptoms: Leaf spots are small and brown, black or red, and
more numerous on leaf tips. The centers of the leaf spots fall
out, creating a “shothole” effect. Infected leaves may turn
yellow and fall to the ground. Fruit sometimes develops dark
pits in the skin.
Use of resistant varieties is the primary method of control.
Chemical control is limited. Fixed copper may be used prior
to petal fall. Adequate fertility is important in minimizing
the effects of this disease.
Peach Leaf Curl (fungal)
Symptoms: Infected leaves are thickened, curled and
puckered and often flushed with red or purple. Affected
leaves appear in the spring and drop from the tree.
Using the correct material, a single spray will provide nearly
perfect control, if it is applied during the period from fall
leaf drop until bud swell. After bud swell, the disease cannot
be controlled.
Peach Scab (fungal)
Symptoms: Spots on the fruit are small, dark and circular.
Spots usually do not begin to appear until the fruit is well
grown. They tend to be concentrated at the stem end. The
skin may toughen and crack. Forty to 70 days elapse from the
time the spore lands on the fruit until the spots appear.
The fungus overwinters in twig lesions. The critical period
for control is from the shuck-split stage of development
until 40 days before harvest. Fungicide should be applied at
shuck split and repeated every 10 to 14 days until 40 days
before harvest.
Cherry Diseases
Cherry Leaf Spot (fungal)
Symptoms: Small, circular, purple spots on the leaves. Only a
few lesions per leaf can cause the leaves to turn yellow and
fall. The fruit on trees severely defoliated by leaf spot fail to
mature properly and are soft and watery.
The fungus overwinters in infected leaves on the ground.
Rake and destroy fallen leaves. Apply fungicide, beginning
at petal fall and repeating at 10 to 14-day intervals until
harvest.
Black Knot (fungal)
Symptoms: Elongated swellings or knots on the limbs, twigs
or trunk. The swelling may be less than an inch to more than
a foot long. Newly formed knots are greenish and soft, but
become hard and black with age. Affected limbs die.
The fungus overwinters in the knots. The spores are
discharged from the pink stage of bud growth until terminal
growth stops. Prune out knots and destroy. Since the
fungus may have extended beyond the swelling, make cuts
well below visible infection. Apply fungicide beginning at
the pink stage of bud growth, and repeat at 10 to 14-day
intervals until terminal growth stops.
Tennessee Master Gardener Handbook
497
Table 6. Descriptions of Common Disease Problems and Management Tactics of Fruit Trees
Disease and Description
Management Strategies
Brown Rot, Blossom Blight
See “Peach.”
See “Peach.”
Coccomyces Leaf Spot (fungal)
Symptoms: Reddish spots on leaves drop out leaving circular
holes. This disease is more severe during mild, wet summer
weather.
At bud break, apply fungicide four times at 2-week intervals.
Pear Diseases
Fire Blight
See “Apple.”
See “Apple.” Avoid planting highly susceptible varieties.
Pear Scab (fungal)
Symptoms: Caused by a different fungus then apple scab
fungus. Symptoms are similar, but twig infections can also
occur.
Rake and destroy fallen leaves because that is where the
fungus overwinters.
Fabraea (Entomosporium) Leaf Spot (fungal)
Symptoms: Spots can occur on leaves, shoots and fruit. Spots
are initially purplish-black dots then they become circular,
brown lesions that are about 1/8 inch in diameter.
The fungus overwinters on twig cankers and on fallen
leaves. See “Pear Scab” for control measures.
Plum Diseases
Black Knot
See “Cherry.”
See “Cherry.” Avoid planting highly susceptible varieties
such as Damson, Stanley, Bluefree and Shropshire.
Brown Rot, Blossom Blight
See “Peach.”
See “Peach.”
Bacterial Spot (bacterial)
Symptoms: Can be a severe problem on Japanese plums.
American and European plums are less susceptible. See
“Peach” for symptoms.
See “Peach”. Avoid planting highly susceptible varieties such
as AU Frontier, AU Rosa, AU Rubrum, Frontier, Methley and
Santa Rosa. Some Japanese plum varieties are resistant.
Tennessee Master Gardener Handbook
498
Table 7. Descriptions of Common Disease Problems and Management Tactics of Small Fruit Trees
Disease and Description
Management Strategies
Blackberry Diseasess
Anthracnose (fungal)
Symptoms: This disease can be severe on thorned blackberries
grown in Tennessee. Leaf spots are roughly circular, with a
light gray center and a reddish-purple margin. On the berry,
individual drupelets become purplish brown and sunken after
infection. They eventually become dry and scabby. The most
damaging phase of anthracnose in Tennessee is the berry phase.
Cane Blight (fungal)
Symptoms: Cane blight appears only on fruiting canes. Infection
occurs on primocanes near the end of the growing season.
This disease is most severe when drought stress occurs after
widespread infections take place. Cankers form on the cane,
often at the nodes, and extend down or encircle it. This causes
lateral shoots to wilt and die.
Crown Gall (bacterial)
Symptoms: Wart-like growths (galls) appear on the roots or
crowns of infected plants. Galls range in size from a pinhead
to several inches in diameter. Plants produce dry and poorly
developed berries. Bacteria present either in the soil or on the
planting stock cause galls. The bacteria enter the plant through
wounds or growth cracks.
Orange Rust (fungal)
Symptoms: Orange rust can be a destructive disease on
blackberries and purple and black raspberries. The new leaves
on infected plants are weak, spindly and yellowish. Later, the
underside of the leaves shows orange, blister-like pustles, which
release spores. Canes appear to recover in late summer, but are
still diseased and will not bear fruit the following year. Many of
the erect blackberry varieties grown in Tennessee are resistant.
Sterility (viral?)
Symptoms: The cause of blackberry sterility is not fully
understood, but it may be a virus. Affected plants grow
vigorously, but they either fail to set fruit or they produce fewseeded berries.
Apply a copper fungicide at 10- to 14-day intervals beginning
prior to bloom and continuing through harvest. Destroy
nearby wild brambles. Plant in well-drained site and allow
good air circulation by thinning plants and controlling weeds.
Remove and destroy fruiting canes immediately after harvest.
Cultural methods of control are the same as for anthracnose.
Chemical control is not recommended. Provide drip irrigation
to reduce drought stress. Liquid lime sulfur applied at bud
break in early spring may be helpful. Prune out blighted canes.
Obtain clean planting stock from a reputable nursery and
inspect the roots and crowns for galls. Do not plant in a field
with a history of crown gall. Avoid fields previously planted
with brambles, tree fruits or other highly susceptible hosts.
The practice of mowing blackberry plants after harvest can
cause crown gall problems because of damage to the roots
and crowns.
Key to control: Remove infected blossom clusters before
they open. Apply a copper fungicide at 10 to 14-day intervals
beginning prior to bloom and continuing through harvest. Use
only roots, not plants, for planting stock. Remove and destroy
nearby wild brambles.
Remove and destroy plants that fail to set fruit. Plant only
certified, disease-free planting stock. Destroy nearby wild
brambles.
Blueberry Diseases
Anthracnose (fungal)
Symptoms: This disease is also known as ripe rot. Infected berries
The spray schedule used for mummy berry control will help in
remain symptomless until maturity, when the infected area
controlling anthracnose. Prune out and destroy blighted twigs,
becomes slightly sunken. Masses of salmon-colored spores are
on which the fungus overwinters.
exuded to the surface.
Mummy Berry (fungal)
Symptoms: As berries approach maturity, they become light
pinkish to cream and drop as mummified fruit. Blighting of
leaves, shoots and flowers can occur. The fungus overwinters on
the ground in mummified berries.
Where mummy berry is a problem, early spring cultivation
will aid in control by covering the overwintered berries. Apply
a fungicide from green tip through petal fall at 7 to 10-day
intervals.
Tennessee Master Gardener Handbook
499
Table 7. Descriptions of Common Disease Problems and Management Tactics of Small Fruit Trees
Disease and Description
Management Strategies
Stem Blight (fungal)
Symptoms: One or more branches exhibit yellowed or reddened
leaves, followed by the death of the branch. Stems show brown
discoloration of woody tissue, often only on one side of the
stem. Penetration into the plant is primarily through wounds.
Pruning during the coldest and driest winter months may
reduce infections because inoculum is at the lowest levels
during the winter. Avoid late (early July) fertilizer applications.
These encourage the formation of new shoots that do not
have time to harden off before winter. Winter-injured shoots
are more subject to infection.
Twig Blight (fungal)
Symptoms: Infection occurs in the flower buds and then
advances 2- to 6-inches down the stem, causing a dieback of the
flower bearing stems. The fungus overwinters in twigs infected
the previous year.
Prune and destroy discolored twigs during dormant pruning
and summer. Follow the spray schedule recommended for
mummy berry.
Grape Diseases
Anthracnose (fungal)
Symptoms: This disease is also known as bird-eye rot because of
the dark margin around the gray-colored spot on the fruit. This
disease is usually confined to certain highly susceptible varieties
such as Vidal blanc. Numerous spots may occur on shoots,
leaves, tendrils, petioles and fruit stems.
Bitter Rot (fungal)
Symptoms: This disease can be severe on certain varieties, such
as Catawba. The fungus enters the berry from the stem and a
grayish discoloration of the berry begins on the stem side. The
appearance of tiny, black fungal fruiting bodies and a shriveling
of the berry into a hard, dry mummy can cause this disease to be
mistaken for black rot.
Black Rot (fungal)
Symptoms: Black rot is the most destructive disease of grapes
in Tennessee. Berry symptoms begin as dark, circular spots that
expand to discolor the entire berry. The berries shrivel to hard,
black and wrinkled mummies. Leaf spots are reddish-brown with
dark margins. Dark spots form on the green stems and tendrils.
Crown Gall (bacterial)
Symptoms: Knots form on roots, crowns and sometimes, on
canes. These galls may grow to several inches in diameter. The
amount of damage to the plant varies from none to the death of
the plant. Winter-injured vines frequently become infected.
Eutypa Dieback or “Dean Arm” (fungal)
Symptoms: This disease occurs only in older grapevines because
infections develop slowly. Symptoms consist of dying arms and
yellowed, cupped leaves on new growth in the spring. Leaves
develop small necrotic spots and tattered margins. Infection
occurs on the trunk and main branches through pruning
wounds. Spores are produced throughout the year.
Tennessee Master Gardener Handbook
500
Control needed only on susceptible varieties. Apply liquid
lime sulfur during the late dormant phase, and then follow the
spray schedules.
On susceptible varieties, spray a fungicide in the spring and
summer.
Follow the spray schedules, beginning when shoots are 2- to
4- inches long. Mix a few drops of dishwashing detergent with
the spray solution to improve the coverage of tissues. Good
control in the spring lessens the need for summer control.
Follow recommended pruning practices to properly thin the
canes and avoid overly-dense growth. Destroy pruning and
mummified berries.
Plant winter-hardy varieties, avoid sites with a history of crown
gall and avoid injuries to the canes.
When pruning, make clean, close cuts to encourage callusing.
Identify infected plants in the spring and remove and burn
infected canes when weather is not rainy. Avoid pruning
during the wet weather.
Table 7. Descriptions of Common Disease Problems and Management Tactics of Small Fruit Trees
Disease and Description
Management Strategies
Downy Mildew (fungal)
Symptoms: Light yellow spots form on the upper sides of leaves,
and a white, moldy growth can be seen on the undersides of
leaves. The affected leaves eventually become dry, brown and
crumpled. Defoliation can be severe on some varieties during
wet seasons.
Powdery Mildew (fungal)
Symptoms: This disease usually does not significantly damage
the American varieties. However, many of the vinifera varieties
show a high degree of susceptibility. It appears as a white
powdery growth on the leaves and berry clusters. Severely
affected leaves turn brown and fall.
Use an appropriate fungicide in the spring and summer.
Use a fungicide in the spring according to the label. Continue
use in the summer only if the variety is known to be very
susceptible to powdery mildew.
Raspberry Diseases
Crown Gall (bacterial)
Symptoms: Refer to crown gall of blackberries.
Gray Mold (fungal)
Symptoms: In wet seasons, gray mold can cause a significant
loss of flowers and fruit. Blossoms show a blasting that may
extend down the pedicel. Infected berries become covered with
a gray, dusty fungal growth. Mature berries are more susceptible
than young ones. Berries sometimes do not show gray mold
until after harvest. Berries can quickly become a rotted mass in
storage.
Same as for blackberry.
Avoid excessive nitrogen fertilizer applications. Pick fruit
frequently and early in the day, as soon as plants are dry.
Handle berries with care to avoid bruising. Keep the planting
properly thinned and control tall weeds.
Late Leaf Rust (fungal)
Symptoms: Small pustules filled with powdery yellow spores
form on the underside of leaves, petioles, canes and berries.
The single-crop system of producing ever-bearing varieties
Badly infected leaves drop prematurely. This disease can be
should help control this disease because the fungus is thought
damaging to some varieties of red raspberries, although it occurs to overwinter on raspberry canes.
late in the season.
Orange Rust (fungal)
Symptoms: This rust disease occurs on black and purple
raspberries, but not on red raspberries. Refer to this disease
under “blackberries” for symptoms.
Septoria Leaf Spot (fungal)
Symptoms: This is one of the most destructive raspberry diseases
in Tennessee. Septoria can cause almost total leaf loss, especially
on highly susceptible varieties such as Bababerry. Leaf spots
have tan to gray centers with tiny, black fruiting bodies. Spots
are surrounded by thin, brown to purple borders. The spots are
circular and about 1/8 inch in diameter. Leaf spots are similar
to anthracnose leaf spots on raspberry or blackberry. Heritage
seems to have some tolerance.
Same as for blackberry.
Use a copper fungicide on a 10 to 14-day schedule beginning
in April. Sprays may need to be continued throughout the
growing season, if weather conditions remain favorable for
disease (warm, wet). Remove and destroy fruiting canes
immediately after harvest. Keep the planting properly thinned
and control tall weeds.
Tennessee Master Gardener Handbook
501
Table 7. Descriptions of Common Disease Problems and Management Tactics of Small Fruit Trees
Disease and Description
Management Strategies
Phytophthora Root Rot (fungal)
Symptoms: This disease is usually associated with poorly drained
soils. Affected plants may show a general lack of vigor, or they
Plant only on well-drained sites. Planting on raised beds
may decline and die. The tissue underneath the epidermis on the is helpful, and is important if drainage is occasionally
main roots and crown is a brick red (later turning brown), rather
inadequate. Avoid planting highly susceptible varieties.
than a normal white.
Viral Diseases (Tomato Ringspot Virus, Mosaic and Leaf Curl)
Symptoms: Virus diseases are a major problem in raspberries in
the northern United States, but are relatively minor in Tennessee.
This is presumably because of a lack of the proper vectors. The
viruses most often seen in Tennessee are probably mosaic (a
virus complex) and tomato ringspot.
Plant only certified, virus-indexed stock. Destroy nearby
wild or neglected brambles. Do not plant black or purple
raspberries near red raspberries. This is because reds can
tolerate mosaic and act as a reservoir of inoculum, which will
spread to the black raspberries if the proper aphid species are
present.
Strawberry Diseases
Anthracnose (fungal)
Symptoms: This disease causes the death of blossoms, fruit
clusters and young daughter plants. Dark, sunken lesions form
on all stems, stolons, petioles, peduncles and pedicels. Fruit
lesions are firm, slightly sunken and may be tan, black or natural
in color. The fruit rot phase can occur in the absence of other
symptoms. Leaves shrivel and die due to petiole infections.
Crown infections can result in the wilting and death of older
plants.
Gray Mold (fungal)
Symptoms: This disease can be very destructive in wet seasons.
Gray mold often starts as blossom blight and then continues as
a rot of green and ripe fruit. Many fruit infections begin when
the fungus enters the blossoms and remains latent until the
fruit begins to mature. In wet weather, diseased plant parts
are covered with fuzzy brown to gray masses of fungal spores.
Berries become more susceptible as they mature. Gray mold may
continue to develop after harvest, becoming a rotted mass.
Leaf Spot (fungal)
Symptoms: Lesions are circular, 1/8 inch in diameter and are
purple with a white or tan center.
Leaf Scorch (fungal)
Symptoms: Round to irregular, purple spots, up to 1/4 inch
in diameter, form on the leaf surface. If the spots become
numerous, large areas of the leaf become reddish-purple to
brown and the entire leaf may turn brown and die.
Leaf Scorch (fungal)
Symptoms: Round to irregular, purple spots, up to 1/4 inch
in diameter, form on the leaf surface. If the spots become
numerous, large areas of the leaf become reddish-purple to
brown and the entire leaf may turn brown and die.
Tennessee Master Gardener Handbook
502
This disease is difficult to control. The simplest method
for home gardeners is to replant with one of the resistant
varieties: Delmarvel or Sweet Charlie. On susceptible varieties,
spray with a fungicide during dry weather.
Select a well-drained planting site. Renovate planting properly
to narrow the rows and thin the plants. Avoid excessive
nitrogen fertilizer rates. Mulch to reduce fruit contact with the
soil. Pick berries frequently and refrigerate promptly. Apply
fungicide every 7- to 10- days, beginning at early bloom. Good
protection of the blossoms should eliminate the need for
sprays during harvest. Delmarvel and Earliglow have resistance
to gray mold. Sweet Charlie is very susceptible.
Most varieties show some leaf spot, but no real damage.
Chemical control is not necessary on most varieties. Plant
resistant varieties. Use certified plants and select a welldrained site. Renovate properly to avoid overly dense
plantings. Do not over-fertilize.
Same as leaf spot.
Same as leaf spot.
Table 7. Descriptions of Common Disease Problems and Management Tactics of Small Fruit Trees
Disease and Description
Management Strategies
Leaf Blight (fungal)
Symptoms: Spots begin as circular, purple lesions that develop
brown centers as they enlarge. Lesions near leaf margins become
Same as leaf spot.
V-shaped. Leaf blight develops in hot weather. Older leaves may
become blighted and die in large numbers.
Leather Rot (fungal)
Symptoms: This fruit rot occurs sporadically. Disease
development is very dependent on wet weather and puddled
water. Infected berries are light to dark brown or lilac in color
and become tough and leathery. In the early stages of disease
development, the infected ripe fruit are softer than the healthy
ripe fruit.
Red Stele (oomycete-fungus-like pathogen)
Symptoms: This disease is most damaging in heavy, wet-natured
soils. Plants first appear stunted and dull in color, then wilt and
eventually die. Roots decay and show reddish or brown cores
(steles). Roots become devoid of fibrous lateral rootlets, giving
them a rat-tailed appearance. Red stele is not as common as it
once was because many of today’s varieties are resistant.
Verticillium Wilt (fungal)
Symptoms: This disease does not occur frequently on
strawberries in Tennessee because it favors cool weather. The
symptoms are similar to those for red stele, except Verticillium
does not cause red discoloration in the roots.
Provide good soil drainage. Straw mulches are particularly
effective in controlling this disease. Avoid excessive nitrogen
fertilizer applications.
Avoid sites having low-lying clay soils. Plant on raised beds.
Purchase certified disease-free plants of resistant varieties. Do
not plant in fields with a history of red stele. The casual fungus
can remain in the soil up to 13 years.
Adequate control can be obtained without fumigation
by planting resistant varieties and avoiding sites next to
susceptible crops such as: tomato, potato, eggplant, okra and
pepper.
Tennessee Master Gardener Handbook
503
Table 8. Descriptions of Common Disease Problems and Management Tactics of Vegetables
Disease and Description
Management Strategies
Potato Diseases
Early Blight (fungal)
Symptoms: Initial infection occurs on lower leaves. Lesions
appear small and dry and become dark brown and circular.
Concentric rings give infected leaves a “bulls-eye” appearance.
Leaves turn yellow, brown and then die.
Plant disease-free seeds in well-drained soils. Spray with
protectant fungicides. Control weeds around plants. After
harvest, plow under all plant debris. Rotate crops and take care
to not bruise tubers.
Late Blight (oomycete)
Symptoms: This disease causes pale green spots on the edges
of leaves. Spots appear water-soaked. Lesions are circular or
Spray appropriate fungicide before infection. Applications
irregular and are often surrounded by a yellowish border. Lesions
should be made early in the season on a weekly or bi-weekly
eventually turn purplish to blackish and may be ringed with
schedule. Destroy and bury infected parts of the plant.
a grayish fungal growth. Infected tubers have brown, dry and
sunken lesions.
Virus Y (viral)
Symptoms: This disease causes leaves to be necrotic, especially
at the terminal end. Leaves may also be wrinkled, distorted or
droopy. Stunting and decreased yield may occur.
Plant early in the season. Spray with appropriate fungicide.
Destroy infected plants after spraying with a pesticide. Treat
for aphids.
Sweet Potato Diseases
Bacterial Soft Rot (bacterial)
Symptoms: Infected roots are light brown with dark brown
margins and watery with black streaks, they usually decay.
Lesions may also appear on the stems and petioles.
Black rot (fungal)
Symptoms: Initially, this disease causes circular, small, slightly
sunken, dark brown spots to appear on the surface of the
potato. The rot is usually firm and not deep.
Java Black Rot (fungal)
Symptoms: Affected roots turn yellow, to reddish brown, to
black, to mummified. As the disease progresses, dome shaped,
black fungal masses appear on the root surfaces.
Carefully handle the sweet potatoes, select disease free roots,
do not immerse the sweet potatoes in water.
Rotate crops, use healthy plants for propagation, cure roots
immediately after harvest, use a post-harvest fungicide dip and
sanitize all equipment.
Plant crops in well-drained soils and store harvested sweet
potatoes at 55-60 degrees F and 90% relative humidity. Also,
cure sweet potatoes immediately after harvest and properly
sanitize all equipment.
Tomato Diseases
Bacterial Wilt (bacterial)
Symptoms: This disease causes plants to wilt and die quickly.
Early in the infection, the center of the stem appears watersoaked; later in the disease, it appears brown and may hollow.
Buckeye Rot
Symptoms: Initially, lesions are firm, smooth, brownish and
water-soaked. They appear near the blossom end of the plant.
As the disease progresses, the lesion enlarges and forms into a
target pattern.
Tennessee Master Gardener Handbook
504
Rotate crops, fumigate the soil, remove wilted plants and
replace the soil surrounding them.
Maintain adequate soil drainage, avoid soil compaction,
rotate crops, minimize contact of fruit with the soil and apply
fungicides as appropriate.
Table 8. Descriptions of Common Disease Problems and Management Tactics of Vegetables
Disease and Description
Blossom-end Rot (lack of calcium)
Symptoms: This disease causes a brown to black, leathery rot
near the blossom end of the fruit. The lesion is initially about a
half inch, dry and brown. It gets bigger as the disease worsens.
Lesions may be covered with a black mold.
Management Strategies
Maintain the soil at a pH of 6.0-6.5, make sure plants are
fertilized and watered properly.
Early Blight (fungal)
Symptoms: This disease causes brown target spots that progress
to blighted foliage.
Rotate crops, plant disease-free seeds and apply fungicides as
appropriate.
Late Blight (oomycete)
Symptoms: This disease causes lesions that are large, irregular
and gray with white mold. The fruit will be firm and rotted.
Use disease free plants and seeds and apply fungicides as
appropriate.
Pith Necrosis (bacterial)
Symptoms: This disease causes infected plants to yellow and
wilt. Younger leaves are affected first. The main stem may be
hollow and have black streaks.
Southern Blight (fungal)
Symptoms: This disease causes the yellowing and wilting of
infected leaves. The stems of infected plants look sunken, soft
and black.
Spotted Wilt Virus (viral)
Symptoms: Symptoms of this disease vary, but can include
yellow or brown rings, black streaks on stems or petioles, and
stunting of the plant. Plants may also have one-sided growth.
Fruits may be mottled and discolored.
Plants usually outgrow this condition. However, avoiding
excessive amounts of nitrogen may minimize this disease.
Rotate crops, bury crop debris at the end of the season, apply
appropriate fungicides and fumigate the soil.
Sanitize all equipment, remove and destroy infected plants
and control insects, especially thrips.
Tennessee Master Gardener Handbook
505
Table 9. Descriptions of Common Disease Problems and Management Tactics of Beans and Cabbage
Disease and Description
Management Strategies
Bean Diseases
Anthracnose (fungal)
Symptoms: This disease causes sunken, reddish to black lesions
on the bean pods, leaves and stems.
Bacterial Blights (bacterial)
Symptoms: This disease causes large, brown, circular spots on
the leaves and bean pods. Lesions may be surrounded by a
yellow halo.
Downy Mildew (fungal)
Symptoms: This disease causes white, cottony growth on the
bean pods. Infected tissue may be surrounded by a dark red to
purple border.
Fusarium Root Rot (fungal)
Symptoms: This disease causes stunted and uneven plants.
However, it does not cause seeds to rot or seedlings to
dampen-off. Initial symptoms are long, narrow dark red streaks
on taproots and hypocotlys.
Powdery Mildew (fungal)
Symptoms: This disease causes small, round and whitish spots
on the lower leaves.
Rotate crops, plant certified seeds and plants and spray
fungicides as appropriate.
Rotate crops, plant certified seeds and plants and spray
fungicides as appropriate.
Plant resistant varieties, seed with disease-free seed, rotate
crops and spray fungicides as appropriate.
Use resistant varieties, plant in well-drained, well-maintained
soils and avoid soil compaction.
Spray with a fungicide, use resistant varieties and provide
adequate plant nutrition.
Pythium Root Rot (fungal)
Symptoms: The seeds and roots are the main sights of infection.
Provide adequate plant nutrition and spray fungicides as
Infected seeds are soft and discolored. Infected roots are
appropriate.
colorless to dark brown and appear water soaked.
Rhizoctonia Root Rot (fungal)
Symptoms: Infected roots and hypocotyls have small, narrow,
sunken, dark reddish to brown lesions. Plants may be stunted.
Rust (fungal)
Symptoms: This disease causes powdery, rust colored lesions
to appear on the leaves. Eventually, infected leaves turn yellow,
dry-out and drop.
Bean Common Mosaic Virus (BCMV) and Bean Yellow Mosaic
Virus (BYMV) (viral)
Symptoms: These viruses cause plants to be stunted, bushy and
produce decreased yields. Infected leaves are mottled or mosaic
and may be puckered.
Plant in a shallow, well-drained soil, rotate crops and spray
fungicides as appropriate.
Rotate crops, control weeds, use resistant varieties and spray
fungicides as appropriate.
Use resistant varieties, control aphids and use virus-free seed.
Cabbage Diseases
Black Rot (bacterial)
Symptoms: This disease causes necrotic, V-shaped areas on the
leaf edges.
Tennessee Master Gardener Handbook
506
Rotate crops, plant certified seeds and resistant plants in welldrained soils.
Plant resistant varieties, rotate crops and fumigate the soil.
Table 10. Descriptions of Common Disease Problems and Management Tactics of Cucumberbitss
Disease and Description
Management Strategies
Cucumber (Squash) Diseases
Alternaria Leaf Spot (fungal)
Symptoms: This disease causes tan to brown leaf spots with
concentric, dark rings.
Rotate crops, plant disease-free seeds and resistant varieties in
fertile soil. Spray fungicides as appropriate.
Angular Leaf Spot (bacterial)
Symptoms: Lesions are angular and grayish brown. Fruit has
small, water-soaked spots.
Rotate crops, plant disease-free seeds and resistant varieties in
fertile soil. Spray fungicides as appropriate.
Anthracnose
Symptoms: This disease causes brown, angular leaf spots and
sunken spots on fruit.
Rotate crops, plant resistant varieties and disease-free seeds.
Spray fungicides as appropriate.
Bacterial Wilt (bacterial)
Symptoms: This disease causes individual runners to quickly
wilt and die.
Downey Mildew
Symptoms: This disease causes yellow to brown spots on the
upper surfaces of leaves. Infected leaves may die.
Fusarium Wilt
Symptoms: Plants wilt and then die. Vascular tissue is light
brown.
Gummy Stem Blight (fungal)
Symptoms: This disease causes brown spots on the leaves. Stems
have cracks with a gummy ooze.
Mosaic Virus
Symptoms: This disease causes leaf blades to become long and
skinny. Leaves may be mottled.
Powdery Mildew (fungal)
Symptoms: This disease causes a white, powdery mold to
appear on leaf and stem surfaces.
Control cucumber beetles.
Rotate crops, plant disease-free seeds and resistant varieties in
fertile soil. Spray fungicides as appropriate.
Plant resistant varieties and rotate crops.
Rotate crops and spray fungicides as appropriate.
Control aphids.
Plant resistant varieties and spray fungicides as appropriate.
Tennessee Master Gardener Handbook
507
Table 11. Descriptions of Common Disease Problems and Management Tactics of Grass and Grains
Disease and Description
Management Strategies
Turfgrass Diseases
Brown Patch (fungal)
Symptoms: This disease causes small, circular, 1 to 3 inches
lesions to develop on short cut grasses. Grass may be killed to
the soil surface. On taller cut grasses, larger patches of bleached
grass occur. Lesions are light tan and often have a dark margin at
the edge.
Dollar Spot (fungal)
Symptoms: This disease causes brown patches, up to 3 feet in
diameter, to develop during hot, wet weather. Brown patch is
the most serious disease during the summer on tall fescue in
Tennessee. Some green leaves are usually are present in the
brown patches.
Fairy Rings (fungal)
Symptoms: Fairy rings may appear as small to large rings of
very green grass, dead grass, mushrooms or puffballs, with little
effect on the grass. The soil in the rings may become very dry
and difficult to wet during the summer and fall. Rings can vary
in size from 1 foot up to more than 100 feet in diameter. Some
fairy rings continue to enlarge for many years with an increase in
diameter of 1 to 2 feet per year.
Fusarium Patch/Pink Snow Mold (fungal)
Symptoms: This disease causes circular patches to develop
during cold, wet weather. Patches are rarely greater then 6
inches without snow cover and up to 2 feet with snow cover.
The grass in the patches appears to be gray or light tan. Patches
become pink to salmon after exposure to light.
Helminthosporium Diseases (fungal)
Symptoms: These pathogens cause leaf, crown and root diseases.
Dark, circular lesions that enlarge and girdle the leaves usually
characterize these diseases. Thinning-out and fading-out
symptoms usually occur during stress periods. These pathogens
may also cause seedling blights on recently planted turfgrasses.
Powdery Mildew (fungal)
Symptoms: This disease causes a white to gray, powdery growth
of fungus mycelium on infected leaves. Heavily infected leaves
turn yellow and die slowly. Lower leaves are generally affected
more than upper leaves. This disease is also common on grains.
Tennessee Master Gardener Handbook
508
Provide adequate nitrogen fertilization and soil moisture
levels. Spray fungicides as appropriate.
Provide proper good soil drainage and soil pH. Low levels of
nitrogen will help reduce the severity of brown patch on cool
season grasses. Spray fungicides as appropriate.
Remove large sources of organic matter, such as stumps,
before planting. The removal of excess thatch may help
prevent development in established turf. Aerification and
extra watering of the rings may help the grasses outgrow the
dam-age. Soil fumigation, soil removal or turf renovation by
rototilling can also help control fairy ring. Some fungicides
may also help control fairy rings.
Avoid heavy applications of fertilizer before cold, wet weather
or before the first expected prolonged snow cover. Mow the
grass until growth stops; this will prevent a build-up of excess
foliage. Remove fallen leaves during the autumn and winter.
Fungicides must be applied before snow cover to prevent
disease development under snow. In areas that snow cover
is not a problem, certain fungicides can be applied when the
disease is first observed.
Apply fertilizer to encourage uniform growth while avoiding
excess growth, especially in the spring and summer. Turf
should be irrigated as infrequently as possible, without
causing drought stress. Plant resistant cultivars. Spray
appropriate fungicides at the early form of development.
Provide adequate light intensity and air movement. Select the
most shade tolerant cultivars and apply appropriate fungicides.
Properly fertilizing to avoid lush growth, increasing the mowing
height and irrigating to prevent drought stress will help
infected plants overcome this disease.
Table 11. Descriptions of Common Disease Problems and Management Tactics of Grass and Grains
Disease and Description
Pythium Blight (fungal)
Symptoms: Pythium blight first appears as small, circular patches
from 1 to 12 inches in diameter. Patches often resemble the early
stages of dry wilt. This disease spreads rapidly in streaks along
drainage patterns. Gray, cottony mycelium may be seen in the
affected areas during very humid weather. Root rot type diseases
that are caused by several Pythium species may develop during
hot or cold, wet weather. These diseases can result in a thinning,
or a decline, of turf.
Rust (fungal)
Symptoms: This disease causes small, yellow flecks to develop
on the leaves and stems. Eventually, spots on the leaves become
larger and the yellow areas develop raised centers. Infected
plants become yellow and weakened and may die during stress
periods. This results in thin and weak turfs. This disease is also
common on grains.
Spring Dead Spot (fungal)
Symptoms: This disease first appears as dead spots in 3- to 5year-old turf in the spring, as bermudagrass resumes growth
from winter dormancy. The spots expand for 3 to 4 years. After
the second or third year, the disease often appears as rings of
dead grass and then disappears after 3 to 4 years. Bermudagrass
usually grows over the spots slowly during the summer. The
infected areas often remain lower than the surrounding grass.
Weeds frequently invade these spots.
Management Strategies
Select proper fungicides and use them in a preventative
program during favorable weather conditions for Pythium
blight. Planting cool season grasses in the fall will help prevent
severe seedling blight. Good soil and air drainage and low
levels of nitrogen will help reduce the severity of this disease.
Some cultivars are resistant to rust and should be used when
available. Several fungicides can be used to control this
disease. Proper fertilization and irrigation will help reduce
damage from rust. Leaves should be kept free of water as
long as possible by watering in the morning, by improving air
drainage and by removing excess shade.
A fungicide may be used for control. Reduced levels of
nitrogen and thatch removal may reduce the severity of this
disease. Practices that increase winter hardiness, such as
applications of potassium fertilizer in late summer and higher
mowing heights, will help reduce the severity of the disease.
Tennessee Master Gardener Handbook
509
X
X
Dollar Spot, Lanzia
spp. and Mollerdiscus
spp.
Wet weather, heavy dew and low N
fertility
Fairy Rings, Marasmius
sp., Lepiota sp. and
Wet weather
Psalliota sp.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Helminthosporium
Diseases, Bipolaris
spp., Drechslera spp.
and Exserohilum spp.
Wet weather
Powdery Mildew,
Erysiphe graminis
Cool, moist conditions
Pythium Blight,
Pythium spp.
Hot, wet weather, saturated soils and
high N fertility
X
X
X
X
X
X
Rhizoctonia Brown
Patch Rhizoctonia spp.
Warm, wet weather and high N fertility
X
X
X
X
X
X
Rusts, Puccinia spp.
and Uromyces spp.
Shade, high humidity and low N fertility
X
X
X
X
X
Spring Dead Spot
Cold winter and high N fertility
Stripe Smut, Ustilago
striiformis
Cool, wet weather
Although take-all patch is initiated in
Take-all Patch,
spring and fall, severe damage may not
Gaeumannomyces spp. appear until plants experience heat and
drought stresses
White Patch,
Melanotus spp.
a
b
Daytime temperatures above 85 degrees
F with nighttime temperatures above 70
degrees F and low N fertility
X
X
X
510
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Summarized from: Windham, A. 1996. Turfgrass Diseases and Their Control. The University of Tennessee Agricultural Extension Service, PB842
X indicates that environmental conditions this month often favor disease development.
Tennessee Master Gardener Handbook
Dec.
Wet leaves for an extended period of
time (e.g. 10 hours a day for several days),
low cutting height and high N fertility
X
Nov.
Curvularia Blight,
Curvularia spp.
Oct.
X
Sep.
X
Aug.
June
Xb
July
May
Basal rot - air temperatures of 60 to 75
degrees F. Leaf blight - wet leaves and
successive daytime temperatures of 85
degrees F
Mar.
Anthracnose,
Colletotrichum
graminicola
Feb.
Factors Favoring Disease
Development
Jan.
Disease (Cause)
Apr.
Table 12. Factors Favoring the Development of Several Turfgrass Diseases and the Time Each Disease Usually Occursa a
X
X
X
X
X