WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Bloom

Decision Making Matrices

 

Pest
Brief Description
Damage / Reason for Concern
Monitoring Approaches
Decision Points / Tolerances
Management Options
Follow Up
INSECTS

 

Aphids

Winged and non-winged aphids may be present at this time.

Deformation of leaves.
May cause honeydew formation and sooty mold on fruit.
May transmit viruses.

Check 5 leaves at each plant for adults and nymphs.  Record # of leaves with more than 5 aphids.

Consider  treatment if:
When not in a scorch area: if 50% of leaves sampled have more than 5 aphids.
When in a scorch area: if 10% of leaves sampled have more than 5 aphids.

Reduce excessive nitrogen use.  Aphids (and other piercing/ sucking insects) are attracted to high nitrogen tissues.

Chemical control.

Continue scouting for winged and wingless populations.

Wintermoth and Spanworm

Larvae may be feeding on flower buds.  Larvae are pale green with three white stripes developing on each side.
Head capsules of wintermoth are pale green.
Bruce spanworm larvae have dark head capsules which can lighten to pale green.

Larvae can defoliate new growth and flower buds causing a reduction in yield.

Inspect 5 flower clusters per plant.  Look for feeding activity such as silk, frass, discolored buds and chewed entrance holes in the sides of buds.
Record # of infested or damaged fruit clusters.

Consider treatment if 5-10% of plants have infested buds.

Chemical.
Be cautious of applying pesticides that may disrupt pollinators.

Treated fields should be scouted soon after treatment to determine efficacy.

Leafrollers (OBLR)

Larvae are about 1” long and are green with a dark head. Larvae create webbing on leaves and flowers and feed inside of this shelter.

Larvae can feed directly on fruit to reduce yield.  They can also act as a contaminant pest.

Place pheromone traps to determine timing of larval presence. Inspect 5 flower clusters per plant at each site.  Gently pull apart clusters to look for larvae and feeding damage.  Record # of infested clusters.

Detection of leafroller larvae at most sites indicates pre-bloom insecticide application may be necessary.

Microbial insecticide B.t. with spreader sticker on cloudy day.

Chemical control.

Continue scouting for larvae at each site.

Gall Midge

Insects are very small; they can be seen with hand lens and appear as a small maggot at this stage.
Damage appears as blackened tips of unfolding leaves.

Can cause damage to shoot tips and cause a witches’ broom growth.  This may result in decreased growth and poor bud set for the following year.

Inspect 5 shoot tips per plant at each site.
Look for blackened tips of developing shoots.  If seen, open up tips and use hand lens to identify maggots.

New Planting: When more than 4 tips per plant with distortion. Pest is not an economic issue on established plantings.

Chemical control.  No pesticides are labeled for Gall midge, but other insecticides may have activity against gall midge.

Main peaks of infestation are before and after harvest, when shoot tips are actively growing.  Scout during this stage and again post-harvest.

Root Weevils

Adult black vine weevils, clay colored weevils, and strawberry weevils will be emerging at this time.  Black vine weevils are the largest (up to 1/3” long) and are predominantly black.
Clay colored weevils are mottled light and darker brown or gray.
Strawberry weevils are black to brown in color and 1/5” long.
C-shaped larvae are grubs found in the soil approximately ½” long.

Adult weevils can cause notching damage to leaves and new stems.
Larvae feed on and damage roots.

Look for plants with reduced vigor.  Dig around base of plant to look for grubs feeding on roots.
After May, look for notching on lower leaves and new shoots.
At night, look for adult weevils feeding on foliage by shaking plant onto light colored cloth or using beating tray.

Consider treatment if plants show signs of low vigor and weevils (adults or larvae) have been found. Young plants have a threshold of 1-3 weevil larve per plant.

Manage weeds in the infested area to eliminate alternate food sources for adults and larvae.

Chemical: Time insecticides to target emerging adults; will depend on species present.

Continue scouting for adult and larval stages of weevils.

DISEASES

 

Mummyberry

Leaves and blossoms will begin to become infected.  Infected leaves will flag and turn brown.  Infected blossoms turn brown and wither.

Infection of blossom resulting in loss of yield.  Fruit is non-saleable.

Inspect 5 shoots at each plant.  Infection will appear as drooping shoots and the upper surface of the leaves will turn brown from the petiole outwards.

Consider treatment when primary infection is occurring to reduce secondary infection.

Chemical

Continue scouting for infected leaves and shoots and look for infection on developing fruit.

Godronia Canker

Infections form a bull’s eye pattern and are formed at lea scars and other wounds on stems.

Stem girdling when cankers get large.

Inspect 20 plants per site.  Look for infections on current year stems or wounded areas.

No tolerance established.

Prune out infected wood.
Choose resistant varieties.

Educate farm workers on identification of cankers and pruning out methods.

Botrytis

Blossoms are susceptible to infection.  The pathogen can move from the blighted blossom to the peduncle to girdle the stem.

Stem girdling.
Blossom infection causing poor fruit set.

Fruit may become infected with gray fuzzy mold.

Inspect 5 flower clusters per plant, especially during wet weather.  Look for a brown, water-soaked appearance. Blossoms may also be covered with gray fuzzy mold.

No established tolerance. Consider treatment when twigs are found infected.

Keep an open canopy to allow for good air circulation.
Time overhead irrigation so that foliage is not wet for prolonged periods.

Chemical

Continue scouting for botrytis infection of flowers and fruit.

Bacterial Blight

Reddish-brown to black cankers may have developed from infections in January and February.  Infection only occurs on previous season’s growth and enters through wounds in stem tissue.

Large cankers can cause stem girdling and bud death.

Inspect 20 plants per site.  Look for reddish-brown to black cankers on previous season’s growth. Send samples to lab for diagnosis.

No established tolerance. Threshold depends on market, weather, and variety grown. In mature planting, consider treatment if more then 10% plants are infected.

Prune out infected wood.

Chemical

Educate farm workers on identification and pruning techniques for removal of infected wood.

Anthracnose

Spores are transmitted to flowers and developing fruit during a rain event.  Symptoms are seen on last year’s fruit stems as orange spore masses.

Fruit infection does not usually show up until fruit ripens, sometimes following harvest.

Inspect 20 plants per site.  Look for orange spore masses on last year’s fruit stems.  Look for infected leaves (circular spots) and blossoms turning black or brown.

No established tolerance. Threshold varies according to end product usage and processor.

Apply overhead irrigation so that plants do not stay wet for prolonged periods.

Prune plants to ensure good air circulation.

Chemical

Continue scouting for infection on leaves and blossoms.  Infection on fruit will often not show up until fruit is fully ripened or after harvest.

Shock Virus

Symptoms will be appearing at this stage.  New tissue appears black and older foliage turns orange.  Very little fruit will set.

Decrease in yield for at least one season.  Plants usually recover after one season with symptoms.

Symptoms for Shock Virus are very similar to that of Scorch Virus.  Plants with Scorch Virus will not recover.  Proper identification is crucial.

At each site, look for plants with blackening new foliage and flower clusters.  Tag plants with symptoms and record location.  Send samples off for testing to ensure Scorch Virus is not present.

No established tolerance. Plants with Shock Virus will fully recover.

For small plantings, let disease run its course.  For larger plantings, rogue plants if contained to a small area, otherwise let disease run its course.

Educate farm workers on identification of symptoms and how to mark plants for identification.  Identification should be done throughout the field.

Scorch Virus

Symptoms are similar to those of Shock Virus: shoot tips dying back and blight on blossoms.  Plants will not recover from Scorch as they do from Shock.

Plant death.
This virus can be spread quickly through a field and between fields.  Vectors include aphids and people and tools moving between plants and fields.

Monitoring of plants should be done through the entire field.  Plants suspected for Scorch (or Shock) Virus should be sent to Oregon State University for testing immediately.

Zero tolerance.  

No treatment available for this disease.
Plants must be removed from the field as soon as identified.

Continue monitoring and testing for virus in field.

VERTEBRATE PESTS

 

Voles

Small rodents tunnel through soil causing air pockets in the root zone.  They will also feed on roots

Can eat roots and girdle crowns.

Set up a monitoring station using PVC pipe and apple wedge.  Check for feeding damage on the apple wedge.

20-40% of monitoring stations are positive for feeding damage

Habitat reduction.
Rodenticide baits at bait stations.

Monitor again 2-3 weeks following treatment to evaluate efficacy.

Birds

Several types of birds may be present and have the potential to cause damage in a field. Starlings, robins, house finches, and red-winged blackbirds are common.

Damage to fruit can be caused in several ways; fruit may be knocked off of bushes during foraging, eaten wholly by the bird, or punctured or pecked at by a bird.

Scout for birds in the early morning or just before dusk. Identify type of birds present, number present, and change in population size.

Consider treatment if problematic birds are present. Cater management plan to type and number of birds present.

Several types of management options are available. A management plan should be developed that is appropriate to farm site and surrounding properties.

Continue to scout for birds in the field and adapt management plan accordingly.

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu