OSU BLUEBERRY SCHOOL
March 16-17, 2015
held at
Oregon State University, Corvallis, Oregon
This two-day blueberry “school” was organized for new and experienced blueberry growers,
farm managers, crew leaders, advisors, packers/shippers, and consultants. Experts from Oregon
State University, USDA Agricultural Research Service, Washington State University, and the
blueberry industry were asked to address key issues of where the blueberry market is going; how
you might be more successful in tight labor or volume markets; which cultivars are easiest to
grow and are in most demand; how to establish new acreage using cutting-edge methods;
projected costs and the resources available to growers for selecting new planting sites; how to
best manage existing acreage to maximize returns of high-quality fruit; provide basic information
on blueberry plant physiology to help growers minimize environmental stresses and improve
yield potential; nutrient management programs for optimal growth and quality; irrigation and
fertigation practices for higher quality and better efficiency; use of organic amendments and
mulches; planning for and improving machine harvest efficiency; pruning for hand or machine
harvest (where can you cut corners….or not), maximizing pollination for good fruit and seed set;
overviews of the most important blueberry viruses, diseases, insects, weeds, and vertebrate pests;
and tools for good pest management. Information throughout the program addresses the needs of
conventional, transitional, and organic growers. Simultaneous interpretation to Spanish has been
provided. This proceedings book contains information provided on these topics by each speaker
and co-authors. The thumb drive provided in the registration packet for each attendee includes a
copy of each presentation. Thank you for attending. It is our sincere wish that this will be a very
useful meeting and that you find the accompanying materials a valuable reference! –
Bernadine Strik, Professor and Extension Berry Crops Specialist, OSU and the members of the
organizing committee
Organizing Committee
Bernadine Strik, Chair, Oregon State University (OSU)
Wei Yang, OSU. Co-chair (sponsorship coordinator), OSU
Donna Williams, Rachel Williams & team at OSU Conference Services
Dave Bryla, USDA-ARS HCRU
Chad Finn, USDA-ARS HCRU
Vaughn Walton - OSU
Steve Castagnoli - OSU
Steve Renquist - OSU
Bryan Ostlund – Oregon Blueberry Commission
Eric Pond - industry
Jon Umble – industry
Derek Peacock - industry
Steve Erickson - industry
Nancy Jensen - industry
i
Table of Contents
OSU Blueberry School
Title
Authors
Characteristics of production regions in the Pacific
Northwest
Lisa DeVetter, Pat Jones, Bernadine
Strik, Kathie Dello
1
Markets - what's the future for fresh, processed, and
organic markets? Things you MUST think about before
starting or expanding production
Rod Cook, Derek Peacock, Jeff
Malensky, David Granatstein
9
Cultivar choices- Tried and true to brand new
Chad Finn and Bernadine Strik
15
Economics of production – resources
Bernadine Strik and David Granatstein
29
Resources available for selecting a good blueberry site
Wei Q. Yang
37
Site selection and establishment of a blueberry field
Wei Q. Yang and Bernadine Strik
41
Organic soil amendments and mulches for blueberry:
the good, the bad and the ugly
Dan Sullivan (OSU)
47
On-farm irrigation system design and operation
David Bryla
53
Blueberry plant physiology - why it's important to
understand the plant to manage it well
Bernadine Strik
57
Irrigation scheduling: when, where, and how much?
David Bryla
63
Pruning - impact of plant age, cultivar, and harvest
method
Bernadine Strik
69
Harvesting - hand vs. machine
Bernadine Strik (moderator); Paul
Norris (Norris Farms); Frank Brown
(Littau Harvesters (Inc.); Doug
Krahmer (Berries Northwest)
75
Nutrient management of blueberry -- assessing plant
nutrient needs and designing good fertilizer programs
Bernadine Strik and David Bryla
79
Maximizing pollination in blueberry
Ramesh Sagili, Carolyn Breece, John
Borden
95
Blueberry viruses present in the Pacific Northwest and
suggestions for their management
Robert Martin
99
Blueberry bacterial and fungal diseases
Jay Pscheidt and Jerry Weiland
107
ii
Page
Title
Authors
Page
Weed management for blueberry fields in the Pacific
Northwest
Tim Miller
115
Getting hit high and low: Options for managing bird
and vole damage
Dana Sanchez (OSU
125
Management of arthropods, insect, and plant-parasitic
nematodes in blueberries
Vaughn Walton,Nik Wiman, Inga
Zasada, Joe DeFrancesco, Daniel
Dalton, Amy Dreves, Jana Lee, Lynell
Tanigoshi, Wei Yang
129
iii
Management of arthropods, insect, and
plant-parasitic nematodes in blueberries
Vaughn Walton1, Nik Wiman1, Inga Zasada2, Joe De Francesco3, Daniel Dalton1, Amy Dreves3,
Jana Lee2, Lynell Tanigoshi4, Wei Yang5
1
Department of Horticulture, Oregon State University, 4017 Agriculture and Life Science Bldg.,
Corvallis, OR 97331
2
USDA-ARS, Horticultural Crops Research Unit, 3420 NW Orchard Avenue, Corvallis, OR
97330
3
Department of Crop and Soil Sciences, Oregon State University, 3017 Agriculture and Life
Science Bldg., Corvallis, OR 97331
4
Mount Vernon Research & Extension Center, Washington State University, 16650 State Route
539 Mount Vernon, WA 98273-4768
5
Oregon State University, North Willamette Research and Extension Center, 15210 Northeast
Miley Road, Aurora, OR 97002
INTRODUCTION
There are several species of insects, arthropods and and plant-parasitic nematodes which can
damage blueberries in the Pacific Northwest. Herein, we provide an overview of the most
important pests that attack blueberry. This document classifies pests as direct and indirect. Direct
pests negatively affect fruit quality due to feeding. Indirect pests may affect plant parts including
roots, vascular systems and leaves and may also have a negative effect on fruit quality and
cropping levels. Indirect pests may also be classified as secondary or induced pests when they
are not normally considered a pest, but when their populations increase as a result of broadspectrum or poorly timed insecticide application. Several synthetic insecticides are labeled for
blueberry insect pest control. These compounds need to be used judiciously in order to maintain
high parasitism levels by natural enemies typically found in blueberry fields. Guidelines for the
management of both direct and indirect pests are presented. This document can be used in
conjunction with the Pacific Northwest Pest Management Handbook
(http://insect.pnwhandbooks.org).
The most important direct pests include spotted wing drosophila (SWD), leafrollers, winter
moth, and increasingly there is potential for direct damage from brown marmorated stinkbug
(BMSB). Important indirect pests include root weevils, symphylans, aphids, blueberry gall
midge, scale insects, and plant-parasitic nematodes. Here we describe each respective pest,
indicate how these pests can be detected, and finally discuss some management techniques.
DIRECT PESTS
Spotted Wing Drosophila (SWD)
The invasive species Drosophila suzukii, (SWD) first arrived in the Pacific Northwest in 2009,
and has fundamentally changed pest management in blueberries. These small flies get their name
from the adult male, which has a spot on the leading edge of the forewing. Female SWD may lay
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multiple eggs in suitable ripening fruits using a serrated ovipositor. Developing larvae in the fruit
are extremely damaging. Feeding damage by SWD larvae renders infested fruit unmarketable
and reduces processed fruit quality. Presence of SWD larvae in packing-house fruit samples can
cause rejection of a grower’s fruit, as can insecticide residues that exceed the maximum residue
levels (MRL) established by countries importing the fruit. The adult flies are generally present as
soon as the fruit ripen. In very rare cases, early ripening cultivars may escape SWD attack. In
western US production areas, D. suzukii damage may cause up to $500 million in annual losses
assuming 30% damage levels, and $207 million in annual losses in eastern US production
regions. Nationally, crop loss from SWD has been estimated to potentially exceed $718 million
annually, and costs directly related to management practices are estimated to vary between $129
and $172 million (6 to 8% of farmgate value), annually, and ca. $7 million for Oregon
production. These figures clearly illustrate the economic importance of D. suzukii.
Detection. Timing of seasonal trap captures of adult SWD using apple cider vinegar in clear deli
cups differs depending on the production region. In mild regions such as the Willamette Valley,
trap captures start earlier than in regions with colder winter temperatures, such as the inland
areas of eastern Washington. High mid-summer temperatures (greater than 85 °F) may result in
a brief decrease of trap counts. During the latter portion of the season, the trap counts again start
to increase, peaking in the late fall, and eventually decrease at the onset of the cooler winter
period..In regions where colder winter temperatures are experienced, such as eastern
Washington, SWD are found in traps much later in the growing season. Preliminary studies in
Oregon and California suggest that SWD overwinter as adults, although detailed field
overwintering biology is still unclear. There is increasing evidence that D. suzukii may seek
refuge in suitable alternate host plants as a mechanism to survive without optimal food resources
during cold winter temperatures. Work on alternate hosts and cold-adaptation indicates that this
phenomenon may aid the survival of adult flies. Sampling techniques still need improvement
despite extensive efforts to improve trap methodology and fruit sampling protocols. Traps should
aid growers in the timing of management and enable more judiciuos use of insecticides.
Trapping is currently being used by growers to determine presence or absence of SWD, but
management thresholds based on trap catches have not been established. Most growers and
scientists use traps baited with apple cider vinegar or a combination of sugar-water and yeast to
monitor adult D. suzukii flight. However, trapping is not standardized, it is labor intensive, and in
some cases the costs may not justify the benefits for many growers. Trap data have often proven
to be an unreliable warning against D. suzukii attack, especially for susceptible crops in high-risk
habitats. Monitoring fruit infestation levels to guide management may also be impractical as it is
unclear how many samples are required to accurately determine infestation levels. Additionally,
by the time that larvae are detected in fruit, it may be too late to manage SWD because damage
has already occurred.
Management. Pesticide applications have been a key control tactic for D. suzukii. Effective
materials are used to target gravid females and include pyrethoids, carbamates, and spinosyns.
Applications are timed to prevent oviposition on ripening host crops. Many growers in the
Pacific Northwest schedule spray intervals at 4-7 days. Given the limited selection of products
and modes of action available to growers, this prophylactic use of insecticide is unsustainable.
These limitations could ultimately lead to D. suzukii resistance development and may result in
secondary pest outbreaks because of negative non-target effects on beneficial organisms. In fact,
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the first observations of secondary pest resurgence have been reported in several blueberry
production regions nationally. Furthermore, production costs have increased substantially in
susceptible crops where D. suzukii are managed. Pesticide management of SWD on average cost
growers approximately $250/acre per season on Oregon. There are no registered insecticides that
are known to control larvae within fruit. Pesticide sprays only target adults, but this life stage is
estimated to constitute only 5-10% of the total population during the harvest period. In particular,
organic production is seriously threatened because there are few effective organically approved
SWD insecticides. Chemical control presents difficulties in timing insecticide applications for
many crops because of pre-harvest interval concerns. Several exporters in the United States have
lost fruit consignments due to unacceptably high pesticide residue levels as a result of the need to
control SWD close to harvest. Current cultural management practices include timely and costly
repeated harvests to remove fruit before reaching peak susceptibility to SWD. Efforts to
optimize chemical control are currently focused on increased efficiency. Effectiveness of
electrostatic sprays, border sprays, and alternate-row sprays are some examples of these efforts.
Research on parasitoids suggest that there are few species that attack SWD in the US, and their
impact on host populations is very limited. However, the species composition, distribution, and
host range of D. suzukii parasitoids are poorly documented in North America. Parasitoid impact
on populations of D. suzukii is believed to be limited as indicated by a parasitism index from the
sentinel traps. Work on the importation of parasitoids is ongoing.
Brown Marmorated Stink Bug (BMSB)
Another invasive pest and recent arrival in the Pacific Northwest is the brown marmorated
stinkbug (BMSB; Halyomorpha halys (Stål)). BMSB feeds on numerous fruit and vegetable
crops, including blueberries. Direct effects are caused through feeding on berries, while BMSB
also attacks vegetative plant structures, causing indirect effects on plant health. In the Willamette
Valley of Oregon, BMSB has only recently begun to threaten agriculture, although nuisance
problems in urban areas have been occurring for several years. This pest is currently increasing
in range into other important blueberry production regions including parts of Washington and
California. About 28 eggs are laid per cluster on the undersides of leaves. The eggs are various
shades of blue or green and are barrel-shaped. After several days the eggs hatch and the red or
orange first instar nymphs form a ring around the egg mass as they feed directly from the eggs.
After molting, the black second instar nymphs disperse across the host plant and begin feeding
on the plant itself. There are five immature stages before the winged adult stage is reached, and
all but the first instar nymph can potentially damage the blueberry crop. Although the different
life stages can differ in coloration and appearance, a white band on the charcoal-colored
antennae is always present throughout development and may be used for identification. Nymphs
move readily across individual plants; however, the winged adults can disperse over long
distances and may frequently move between different host plants. Feeding by adults and
presumably immature H. halys can damage the fruit by causing external discoloration and
internal damage in the form of tissue necrosis. Feeding may also affect ripening and °Brix of the
berry crop. Other potential impacts of BMSB on commercial blueberry production may be
through contamination of the crop with pathogens causing secondary infection, contamination of
fruit by defensive volatile compounds, and by the presence of nymphs and adults at harvest,
particularly in mechanically harvested fruit.
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Detection. The recent discovery and subsequent commercialization of both the aggregation
pheromone and a synergistic compound that can be combined to create a highly attractive lure
has resulted in an effective trap that is available to growers. The standard trap is currently the
large black pyramid trap, though other designs also work well. All of the commercial lures based
on the newly discovered aggregation pheromone and the synergist that are currently on the
market work well. However, little data is available to link trap captures to management activity.
The traps can be used to determine presence or absence of BMSB, or to determine relative
abundance of nymphs or other life stages, as instars 2-5 and adults are attracted to traps. It is
recommended that traps not be placed directly in the crop. Aggregation pheromone attracts the
bugs within 2-3 yards of the trap, and the majority of these BMSB will not likely be captured in
the collection jar. Instead, they may cause crop damage that would not have otherwise occurred.
In general, it is best to place traps along borders of crops, particularly where there is natural
vegetation or forest as this will be the likely source for BMSB immigrating into berry fields. The
standard black pyramid trap requires that a killing agent be used in the collection jar. This
effectively prevents the captured insects from escaping. Other traps may not require a killing
agent, but then the traps should be monitored frequently as it is likely that some insects will be
able to enter and exit the trap. Other methods for sampling and detection include use of beating
trays and timed visual observations. Beat samples of vegetation surrounding berry fields can be
very effective to determine presence of BMSB along borders. Target wild host plants with fruits,
seeds, or pods such as wild Himalaya blackberry, big leaf maple, or tree of heaven. Beat trays
can also be used to dislodge BMSB nymphs and adults directly from blueberry plants. Repeated
2-3 minute visual observation of blueberry plants can be used to determine presence or absence
and relative abundance of all life stages on blueberry plants.
Management. There are few management options at this time for BMSB. Chemical management
is the typical response. Effective chemistries are neonicotenoid and pyrethroid insecticides.
Guidelines for effective management of SWD can also help to prevent BMSB damage. However,
there are no good organic insecticides for BMSB, so organic management of SWD that is largely
dependent on spinosad compounds will not likely affect BMSB. Border sprays and alternate row
sprays show promise because these approaches have been shown to be effective in other
perennial crops. There are few natural enemies of BMSB in the Pacific Northwest. Parasitism on
egg masses is very low, although predation of eggs can be high in some locations. Thus, it is
important to conserve natural enemies, particularly generalists such as lacewings, spiders, ground
beetles, and earwigs. Current management tactics under research include attract-and-kill
techniques, as well as a classical biological control program for Trissolcus japonicus, a minute
egg parasitoid that attacks >50% of BMSB eggs in China.Originally a candidate biological
control agent under testing for eventual release in the US against BMSB, this parasitoid has been
recently discovered in a Maryland forest remnant.
Leafrollers
Leafroller larvae roll and tie terminal leaves together for shelter and feeding. Two leafrollers that
are damaging to blueberries in the Pacific Northwest are the orange tortrix (OT; Argyrotaenia
citrana) and oblique-banded leafroller (OBLR; Choristoneura rosaceana). Direct damage to
blueberry fruit occurs occasionally when leaves are tied to flowers or fruit. Larval feeding on
berry clusters or flowers is also believed to promote the spread of fruit diseases, including
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botrytis. Furthermore, OT larvae can become contaminants of mechanically harvested fruit.
Caterpillars are light cream to green in color with light brown heads. They have three pairs of
thoracic legs and five pairs of fleshy pseudolegs on the abdomen. Four pairs are near the true
legs, and the fifth pair is located on the tail end. Less than 0.06 inch long upon emergence from
the egg, the larvae can reach nearly 0.5 inch at maturity. OT undergoes two to three generations
per year. The larvae feed and overwinter on many plant species. In blueberry fields, they may
overwinter on leaves on the soil surface or on the plants inside curled dead leaves. OT larvae can
occasionally be active in the winter, feeding on dead leaves or tender limb tissue during warm
periods. Larvae become active in the spring as new plant growth appears. Peak spring emergence
of OT moths usually occurs from late April through May. OBLR caterpillars are similar in size
to OT but are a darker green with dark brown to black heads. They have the same physical
arrangement and number of legs as OT. Adult moths of both species are buff-colored, with
wingspans that vary from 0.5 to 0.75 inch. Subtle differences in markings on the wings of the
two species serve to distinguish them from one another. The two species have distinct
pheromones, so OT and OBLR lures placed in different traps will allow growers to distinguish
which moths are present in their fields. OBLR has two generations per year. Similar to OT,
OBLR overwinters in the larval stage on various plant species. It usually is inactive during the
winter. This leafroller has a wide host range, but prefers plants in the rose family. Infestations of
blueberries are rare and may be the result of immigration from surrounding areas.
Detection. Rolled leaves and feeding damage of early spring growth may indicate presence of
leafrollers. Infestations are likely to occur near field borders. Control measures should be
considered if more than 5% of the terminals, floral structures, or berries have damage or larvae.
Inspect mechanically harvested plantings for larvae beginning 2 weeks before harvest to
determine whether larvae will be problems as contaminants. Place a white sheet on the ground
underneath plant foliage on a warm day and shake the plants vigorously. Larvae will spin down
on silk threads. Temperature records (degree-day accumulations) and pheromone traps can be
used to time control measures and monitor both species, although OBLR rarely occurs as a pest
in blueberries. OT and OBLR pheromone traps should be placed in the field by April 1 each
year. Apply conventional or biological insecticides, such as formulations of Bacillus
thuringiensis, 2-3 weeks after flight peaks are recorded or as soon as possible when 70 or more
OT moths per trap have been captured within a week.
Management. Larvae are susceptible to low winter temperatures and ice storms. Studies have
shown that more than 90% mortality occurs in larval populations exposed to low winter
temperatures as low as a mean daily temperature of 27°F for two weeks. Removal of larval
overwintering sites (such as leaves plastered to whips or rolled leaves that dropped to the
ground) reduces infestations the following year that would have arisen from an in-field
population of OT. B. thuringiensis can provide excellent control of leafrollers and is most
effective when application is timed to the period when young larvae are feeding. Thorough
coverage and spray penetration into rolled leaves are essential to control. A suitable sticking
agent and application on a warm evening around dusk enhances effectiveness. Control is
enhanced if the guidelines for the use of B. thuringiensis are followed. Timing of applications
may be improved by using thresholds from pheromone traps. Consider the use of B. thuringiensis
if leafroller control is required when pollinators are present and avoid insecticide application
during bloom to protect pollinating insects.
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Winter moth
Four species of inchworms or spanworms (Operophthera spp.) injure blueberries. All stages of
these species are similar in appearance, and their larvae cause the same type of damage. Adults
are called winter moths because of late fall and early winter male flights. Larvae are pale green
with a light colored line down the side of the body. They vary in length from less than 0.06 inch
upon hatching to over 0.5 inch at maturity. Larvae have pale green heads, three pairs of true
thoracic legs, and three pairs of fleshy pseudolegs on the abdomen. Larvae damage buds, bloom,
leaves, and fruit from late March through midsummer by boring into developing buds, fresh leaf
growth, blooms, and small berries. Leaves are tied together with silken threads, but not rolled as
with leafrollers. Flightless females lay eggs on trunks and stems of many species of deciduous
trees and shrubs in late fall and winter. Eggs hatch in late winter and early spring. Larvae are
found on host plants through late spring or early summer, and pupation occurs in the soil to
complete one generation per year.
Detection. Inspect plants at weekly intervals in late March to early April around the field
borders, focusing particularly on nearby deciduous broadleaved trees and shrubs. Look for dead
or dying buds, damaged buds with tunneling, leaves webbed together, and the presence of larvae.
Management. Biological control does not consistently limit pest populations below economic
thresholds. Naturally occurring predators including lacewings, assassin bugs and spiders feed on
larvae. Parasites of larvae are not common. Bacillus thuringiensis and registered conventional
insecticides give good control when applied sufficiently early in the season. Best results are
obtained when sprays are applied to small larvae. Larger worms are more difficult to control.
Warm temperatures and dry weather also enhance control.
INDIRECT PESTS
Root Weevils
There are three species of root weevils (Otiorhynchus spp.) that cause damage to blueberry in the
Pacific Northwest. Black vine weevil (BVW; Otiorhynchus sulcatus), strawberry root weevil
(SRW; Otiorhynchus ovatus), and rough strawberry root weevil (RSRW; Otiorhynchus
rugosotriatus) are the most economically important. Larvae of all species are similar in
appearance, occurrence, behavior, and damage caused to the plant. They vary in length from less
than 0.06 inch when newly hatched to over 0.5 inch when fully grown. They are C-shaped,
cream-colored with brown heads, and have no legs. BVW is the most common weevil found to
infest blueberries. Adults are nearly 0.5 inch long, black to gray-black in color, and have a few
orange or yellow specks on the wing covers. SRW and RSRW are about 0.25 inch long and vary
from reddish-brown to nearly black. Economic damage can occur when adults girdle twigs
bearing berries or when adults are a contaminant during mechanical harvest of the fruit. Weevils
spend the winter as larvae in the soil and feed upon roots during this period. The larvae cause
damage by feeding on and girdling roots and the basal crown areas. During periods of unsuitable
winter temperatures, larvae may create an earthen cell and remain inactive until soils warm.
Larvae may pupate as early as April, followed by emergence from the soil as adults in July.
Obscure root weevil (ORW; Nemocestes incomptus) is a fourth species of root weevil that
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occasionally causes damage. Adults of this species may emerge later than the other weevils.
Eggs are deposited in or on the surface of the soil in small clusters from June through September.
ORW may also deposit eggs on foliage. All larvae move into the soil and immediately begin
feeding on roots upon hatching. All adult root weevils present in blueberry fields are females and
are capable of laying 200-500 eggs during the course of a 3- to 9-month lifetime. In irrigated
plantings ORW can be found in the soil from late summer through early summer of the following
year, as deep as the root system of the host plant penetrates the soil.
Detection. Field history is very important. During the growing season prior to planting or replanting, inspect the field to be planted with blueberries for adults and larvae. Root weevil
infestations in both prospective and established fields can be detected by a combination of
methods. The females of all root weevil species feed for a 3-5 week period on foliage before
laying eggs. Characteristic marginal leaf feeding can be seen beginning in May. Damage appears
as leaf edge notching on new growth. Females are active at night and during overcast or showery
days of low light intensity. Adults are usually not seen on foliage during the daylight hours,
preferring instead to lie motionless on or below the soil line hidden among plant debris or within
the shelter of cracks and crevices of the plant bark. Plants infested with root weevil larvae are
stunted, yield poorly, and may die. Larvae hatch starting in September and can be seen in
irrigated soils through the following spring. Eggs of root weevils may not hatch in non-irrigated
soil until fall precipitation arrives. Weevil traps can be created by wrapping the trunks of plants
with cardboard or burlap during late May, June, or July. Weevils often congregate here during
daylight hours. Check wraps in the early morning if afternoon temperatures rise above 75°F or if
trunks receive direct sun.
Management. More than 90% of SRW larvae and pupae can be eliminated when a combination
of plowing and rototilling is used in late April/early May. It is important to note that pre-plant
cultivation is most useful for control of pupae. Fall or early spring cultivation of infestations
when only larvae are present may not give the desired degree of control. This is because
undecomposed plant material can remain as a resource for development of surviving larvae to the
pupal and then adult stages. Even at 90% control through cultivation, this method alone may be
insufficient to protect new plantings. Field infestations may be the result of one or a concert of
three primary occurrences: first, planting into a field previously infested with root weevils;
second, introduction of larvae (occasionally adults) on infested rootstock or transplants; and
third, a wide host range, including many species of native and introduced ornamental plants.
Often, infestations result from summer migrations of weevils into a field. Make sure to plant
only material that is certified weevil-free. Small grains are not a host for root weevils so these
may be used as a cover crop on infested sites. Allow at least 12-16 months before planting
blueberries if cultivation or host-free periods are the only techniques used for weevil
management. Control weevils in bordering fields and surrounding vegetation. Commercially
available insect-parasitic nematodes and fungi can provide control but they must be applied at
the correct time during late larval development and when ample soil moisture and warm soil
temperatures predominate. Currently labelled insecticides provide limited control.
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Symphylans
Symphylans (Scutigerella immaculata) are non-insect generalist feeders that injure germinating
seeds, feeder roots and root hairs, tubers, rhizomes, and aerial plant parts that come into
prolonged contact with the soil. Seedlings may die, and surviving plants are stunted and never
fully realize yield potential. Symphylans resemble miniature, swiftly moving centipedes or
millipedes. Symphylans seldom exceed 0.25 inch in length, and newly hatched symphylans have
six pairs of legs, adding an additional pair at each molt (shedding of the skin or outside skeleton)
until the adult stage is reached. At maturity, symphylans have 12 pairs of legs, 15 body
segments, prominent antennae, and a pair of silk-producing structures at their tail ends called
spinnerets. These structures resemble miniature pincers. Features that distinguish symphylans
from other soil arthropods include white to cream body color, very fragile nature, rapid
movements, rapidly vibrating antennae, and immediate movement back into soil when exposed
to light. Field observations indicate there are two distinct periods of egg production, one in the
spring and the other in the fall. The greatest numbers of adult and immature symphylans occur in
the summer and early fall. Symphylans negatively impact newly established seedlings. When
large populations exist at planting (greater than 10 per shovelful of soil), plants remain stunted,
never realizing economic return.
Detection. Prior to planting, consider field history, soil type, injury to previous crops, and
proximity to other symphylan infestations. Clay soils and those rich in organic matter are more
likely to be infested than sandy or mineral soils. Applying mulch and composted manure, may
create an ideal environment for symphylans. Sampling soil with a shovel to a depth of at least 8
inches and sifting it through a series of three screens (the largest with mesh size about 0.5 inch
and the smallest with mesh the size of window screen) onto a black tarp probably is the simplest
and most accurate method for detecting symphylans. Inspect at least 30 sites within the potential
new planting area. Ideally, sample during the summer of the year preceding planting. Sample
when another crop is present and when soil is moist and friable, easily passing through the
screens. Most symphylans will be found in the last screen and the tarp. If 3-5 symphylans are
found per shovelful in many areas of a field, potential for economic damage exists.
Management. Non-chemical controls, with the possible exception of cultivation, usually are
ineffective or impractical in most situations. In fact, no simple, inexpensive, or reliable method
of control has been developed. Pre-plant soil fumigation, when done properly, generally gives
adequate control for a 2- to 3-year period allowing for establishment of the planting. However,
pre-plant soil insecticides are not labelled for use on blueberries. Because symphylans are softbodied and very fragile, frequent, vigorous cultivation when symphylans are in the upper strata
of the soil (April through August) may reduce numbers. Research in the United Kingdom has
indicated that flooding can control symphylans. Soil solarization achieved by covering soil with
clear plastic is unlikely to control symphylans because of their vertical and horizontal mobility.
Aphids
Aphids (Hemiptera: Aphididae) are yellow, red or green- colored, small (< ⅛ inch), winged or
wingless soft-bodied insects that are distinguished by a pair of cornicles (lance-shaped
structures) protruding upward from their tail ends. They are usually found in colonies on new
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shoot growth, buds, undersides of leaves, and near flower and fruit clusters. The green peach
aphid, Myzus persicae, and occasionally Fimbriaphis fimbriata (no common name) occur on
blueberries throughout the Pacific Northwest. The green peach aphid overwinters on bedding
plants in nurseries or on any plant host sufficiently protected from severe winter temperatures.
Fimbriaphis fimbriata probably overwinters on strawberry plants. Be aware of the vegetation
surrounding a planting and its possible role in contributing to aphid infestations. Large
populations of aphids weaken and stunt new shoot growth by removing plant sap. While feeding,
copious amounts of honeydew (a sticky, sugary anal secretion) are released from the cornicles.
The honeydew makes the leaves and fruit sticky, sensitizes plant tissue to sunburn, and promotes
the growth of black sooty mold. Ants, honeybees, and yellowjackets may collect the honeydew.
Honeydew makes both hand-pick and machine-harvest operations more difficult, and the fruit
may be unmarketable or downgraded. Aphids may additionally vector plant viruses to field
plants.
Detection. Inspect blueberry planting weekly, prior to bloom through harvest in numerous
locations, particularly the upwind margins of the field and areas of excessively lush growth.
Because the green peach aphid and F. fimbriata do not over-winter on blueberry plants, the
above locations are the most likely areas of colonization by immigrating winged forms.
Management. Aphid populations increase rapidly on plants receiving excess nitrogen. Prune if
needed to remove suckers and excess growth that enhance the rapid increase of aphid
populations. Encourage natural enemies (predators and parasites) by cultivating a progression of
flowering plants within or near the blueberry planting. Control ants because some species of ants
guard aphid colonies from natural enemies in order to glean honeydew. For small plantings, a
narrow band of Tanglefoot or “stickem” around the base of the plants will exclude ants, as long
as limbs, grasses, or other plants do not form a bridge over or around the sticky band.
Insecticidal soaps, pyrethrum sprays, and forceful overhead irrigation can provide some control.
Contact insecticides can be used for aphid control. Because no systemic insecticides are labelled
for use on blueberries, control using these sprays depends on the solution making direct contact
with the aphids. Application should be applied as needed but should occur before aphid
populations have stunted plants or secreted much honeydew.
Blueberry gall midge
Blueberry gall midge (Dasineura oxycoccana,Johnson) is a minute fly (Diptera: Family
Cecidomyiidae) that can cause significant economic damage to floral and vegetative buds in
some blueberry production regions, such as the southeastern United States as seen in the early
1990’s. In the Pacific Northwest, gall midge is considered a minor pest, causing only occasional
minimal damage to vegetative buds. The damage caused by larval feeding is typically flower
bud abortion and aborted and/or blackened young shoot tips as well as distorted developing
leaves. In heavily-infested fields, a witches-broom’ and branching symptoms may occur.
Growth can be stunted when plants are young, which can be problematic when growers are
trying to maximize vertical plant growth to keep the fruit from contacting the soil, or in order to
mechanically harvest. Damage is rarely economic once plants are established, and may appear
similar to boron deficiency, frost damage, or thrips damage. Thrips damage to vegetative buds,
though similar, typically causes stunting and branching, but not blackened tips. Instead, the
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rasping feeding from thrips is typically evident in close inspection of the margins of the leaves
enclosed in the bud.
Blueberry gall midge is a small fly approximately 2 to 3 mm long. The female lays eggs between
the scales of flower buds after the buds begin to expand. Newly hatched larvae are less than 1
mm long, white, and nearly transparent. They then become reddish-orange second and third
instar larvae, spending 2 to 4 days in each instar. Mature larvae (maggots) are about 1 mm long,
0.3 mm wide, legless, and yellow to red in color. Detection of larvae is difficult because of their
small size, before damage occurs. Larvae cease feeding and form pupae in 7 to 10 days. There
are four or more generations in a growing season, and the final generation of pupae overwinters
in the soil. There are believed to be are two main peaks of blueberry gall midge infestation
during the growing season, preceding and following harvest.
Monitoring. Due to the minimal problems that blueberry gall midge causes in the Pacific
Northwest, it is typically not monitored-for in a standard pest management program. Instead,
sampling is typically used to confirm suspected damage. When damage is suspected, randomly
collect five young growing shoot tips with emerging leaves still rolled from 10 random plants in
the suspected field. Determine the percentage of shoot tip damage by dividing the number of
damaged shoot tips by the total number of shoot tips collected. To confirm the presence of
larvae, store the young growing shoot tips in a 1-gallon resealable bag. Place a piece of folded
moist paper towel in one lower corner of the bag and the shoot tip samples in the other lower
corner. Keep the plastic bags at room temperature. If the shoot tips are infested with blueberry
gall midge, tiny larvae should emerge after 1 to 2 days and adult flies after 2 weeks. The white
and reddish-orange midge larvae can be seen against the clear plastic bag. Adults can be
monitored using sticky traps, but larval sampling is typically preferred.
Management. If an infestation is confirmed and considered to warrant treatment, insecticides are
typically targeted at adults. Larvae are very difficult to control within the buds. Control not
extremely effective during the year an infestation is recognized since different life stages are
present in the field. In the spring following recognition of an infestation, effective control can
often be obtained by targeting the first generation of the adults emerging from the soil, typically
in March and April. Most interestingly, a tiny parasitoid wasp was discovered that kills the
larvae by developing inside the body and eventually killing them.
Scale Insects
Lecanium scales may infest blueberry plants occasionally. Heavy infestations reduce plant vigor
and terminal growth. These scales are about 0.12 inch in diameter and vary from red to dark
brown. Bodies are oval and raised, resembling small helmets or bumps on branches, stems, and
the undersides of leaves. Like aphids, scales also secrete honeydew, which promotes sunburn of
leaves and fruit as well as the growth of sooty mold that affects fruit yield and quality. The outer
covering of the scale is composed of waxes secreted during growth and development, providing
a degree of protection from predators, rain, and insecticides. Usually one generation occurs per
year, with either fertilized females or immature forms overwintering on stems. Development is
completed in the late spring or early summer. In May or June, numerous white to cream-colored
eggs can be found under these scales. Just prior to or during harvest of early-bearing blueberry
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varieties, these eggs hatch, and the young scales, called crawlers, migrate to the undersides of
leaves to insert their piercing/sucking mouthparts into tissue along the larger veins. After 4-6
weeks on the leaves, scales return to stems and twigs. Here they mate and continue to feed
through early fall. Feeding resumes again in the spring, with the cycle repeating itself. Scale
insects disperse as crawlers by movement of people and machinery, wind, rainfall, irrigation, and
hitchhiking on the feet of birds.
Detection. Inspect twigs for scales during the dormant season. Pay particular attention to the
edges of plantings and weak plants, as well as older plantings where some bark and crevices may
occur. The crawlers migrate starting in March and are best observed with 10x or greater
magnification. Often, newly hatched crawlers remain under the mother scale until favorable
weather and warm temperatures stimulate migration. Beginning in May, overturn a number of
scales and check for egg hatch and crawler migration. Tanglefoot, stickem, Vaseline, or doublesided tape can be placed around scale colonies. The young crawlers will become stuck to the
adhesive. Weekly monitoring and replacing of adhesives will help to determine the beginning,
duration, and end of crawler emergence.
Management. Infested plants and old growth should be pruned and severely infested twigs
destroyed. Insecticidal soap can be used for crawler control. Direct contact of the soap solution
with the crawlers and two to three applications timed 7-10 days apart during dry winter periods
should provide some control. Note that thorough coverage and direct contact with the scale
crawler is essential for control. Time sprays to coincide with migration away from the mother
scale. Control of adults is much more difficult. Scales are best controlled during the dormant
season by thoroughly covering infested twigs and branches with either a 3% petroleum oil spray
alone or with an organophosphate insecticide. The oil both suffocates the scale and aids the
passage of the insecticide through the waxy coating of the scale. The solution must contact the
scale directly. Scale insect crawlers are easily controlled with a contact insecticide.
Plant-parasitic nematodes
While diverse plant-parasitic nematodes have been reported from blueberry, the most commonly
encountered plant-parasitic nematodes include root-lesion nematode (Pratylenchus spp.), dagger
nematode (Xiphinema spp.), and stubby-root nematode (Paratrichodorus renifer). Adult
Pratylenchus spp. are migratory endoparasites. Throughout their life, they migrate into, through,
and out of roots, feeding on some root cells and damaging others by tunneling activity. This
extensive damage produces necrotic lesions, reducing the ability of roots to take up water and
nutrients and increasing the susceptibility of roots to attack by soil borne pathogens. In the
Pacific Northwest, several species of root-lesion nematode may be found in blueberry fields
including Pratylenchus penetrans, Pratylenchus neglectus, and Pratylenchus thornei; however,
these species appear not to be parasites of blueberry roots and are likely surviving on weed hosts.
In fact, in controlled experiments Pratylenchus penetrans was not able to survive in pots with
blueberry plants, indicating that blueberry is not a host for this nematode. The root-lesion
nematode species of concern in the Pacific Northwest is Pratylenchus crenatus. The impact that
this nematode has on blueberry establishment and productivity has not been determined.
Xiphinema spp. and Paratrichodorus spp. are migratory ectoparasites, with their bodies
remaining outside the root and only their stylets penetrating the cells of the root. Xiphinema spp.
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may cause damage directly to roots if present in high numbers, but they are most important as
vectors for the tomato ringspot virus. Blueberry plants infected with tomato ringspot virus
display malformed (strap-shaped), chlorotic leaves and necrotic, circular lesions on the stems.
Small populations of these nematodes can cause serious loss where the virus is present,
spreading the virus from plant to plant and from infected weeds to blueberry plants.
Paratrichodorus renifer has been shown to seriously damage blueberry cuttings by severely
stunting the young root system. In microplot experiments this nematode caused 40% yield loss of
blueberry 'Chippewa.'
Detection. Nematode populations fluctuate throughout the year, affecting the number of
nematodes recovered at various sampling times. For example, Pratylenchus spp. populations
peak in the summer while Xiphinema spp. populations are highest in the spring. If both of these
plant-parasitic nematodes are known or suspected to be in field, then sampling in the spring and
the fall may be necessary. The best way to collect soil samples is with a soil probe. Few
nematodes are found in the upper three inches of the soil or in the sawdust mulch. Therefore, it is
advisable to insert the soil probe to a depth of 12-18 inches and remove the top 3 inches cm of
soil (or sawdust) before putting the subsample into the bucket. Each probe full of soil constitutes
one subsample. Taking several subsamples will result in a more representative and accurate
sample. For this reason, collection of at least 20 to 30 subsamples for every 1-4 acres is generally
recommended. Fields larger than four acres should be divided into sections, with separate
nematode samples taken from each section. The subsamples should be drawn from sites chosen
randomly throughout the field, usually by walking in a “W” pattern, and then mixed together in a
clean bucket. Areas with different soil types or cropping histories should be sampled separately.
Management. There are two times during the blueberry production cycle when plant-parasitic
nematodes can be managed, pre-plant and post-plant. It is important to understand that once a
plant-parasitic nematode population is established in a blueberry planting it is very difficult to
eliminate. Great care should be taken prior to planting and in established blueberry plantings to
minimize the introduction of nematodes through infected planting material or dirty equipment.
Before planting, every measure should be taken to create an environment that facilitates rapid
and healthy establishment of blueberry plants. From a cultural management perspective, cover
crops or fallow may be implemented at this time. The use of cover crops has the potential to
reduce populations of plant-parasitic nematodes, but the effect will depend upon the nematode
target. For example, research demonstrated that rotation with tall fescue or rapeseed cover crops
were as effective as soil fumigation in reducing populations of Xiphinema americnum.
Additionally, reinfection of plants with tomato ringspot virus, a virus vectored by X.
americanum, was also prevented for three years. Fallowing is generally considered to be an
effective way to reduce nematode populations because the nematode does not have a host upon
which to survive. Because several cultivated plant and weed species serve as good hosts of plantparasitic nematodes, weeds must be controlled diligently during the fallow year. Pre-plant is the
only time when broad-spectrum fumigants can be applied to manage plant-parasitic nematodes.
In fields where plant-parasitic nematodes are suspected of being a problem, soil fumigation
allows young blueberry plants to become well established while nematode populations are low.
Soil fumigation does not permanently eliminate nematodes from an area; rather, it reduces
population densities during the critical establishment phase. Finally, only planting material
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certified free of plant-parasitic nematodes should be used. There is very little information
available on the susceptibility or resistance of blueberry planting material to plant-parasitic
nematodes. Recent studies showed that the blueberry varieties 'Bluecrop', 'Brunswick', 'Duke',
'Misty', 'O'Neal', and 'Chippewa' were all very good host for Paratrichodorus renifer.
Conversely, it appears that 'Powderblue' is a poor host for Paratrichodorus renifer.
Once a blueberry planting is established there are few practices that consistently and effectively
reduce plant-parasitic nematode damage to blueberry plants. While there are several post-plant
nematicides labelled for use in blueberry, there is limited information available on the efficacy of
these products in a blueberry production system. The best approach to offset or minimize
damage to established blueberry plants by plant-parasitic nematodes is to avoid plant stress
through more frequent irrigation, applying additional fertilizer to support blueberry plants with
limited root growth, and by controlling other diseases and pests.
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