WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Bloom

Biology and Monitoring

 

 
Insects
Diseases
Key Pests
 • Aphids
 • Wintermoth & Spanworm
 • Gall Midge
 • Leafrollers
 • Root Weevils
 • Mummyberry
 • Godronia Canker
 • Botrytis
 • Shock Virus
 • Scorch Virus
 • Anthracnose
Occasional Pests
 • Scale
 • Cherry Fruitworm
 • Tent Caterpillars
 • Sawflies
 • Bacterial Blight
 • Premature Fruit-drop
 • Phomopsis Canker

 

Biology

Aphids

Wingless and winged aphids may be present at this time. Winged aphids are a concern if in an area of blueberry scorch virus. Populations will continue to build throughout the growing season if beneficial populations are not sufficient.

 

Wintermoth and Bruce Spanworm

Larvae prefer to feed on flower buds by tunneling into the bud and feeding on the developing flower parts. During bloom, small larvae can be found inside the flower and in clusters.

 

Leafrollers

All life stages of this pest are present at this time. As leaves expand, larvae roll up leaves to feed and pupate. Second generation adult moths begin to emerge in late May or June.

 

Gall Midge

Adults emerge in May and June to oviposit in the terminal growth of new shoots. Adults are very small gnats, less than 1/16 of an inch long. Eggs hatch within a few days and the tiny larvae feed in the terminal buds causing the foliage to curl and deform. This feeding may also cause branching or witches’ broom symptoms resulting in decreased plant growth and reduced bud set for the next season.

Early larval stages are clear to ivory; as they mature, they become pink or orange in color and are only 1/16 inch long at maturity.

Gall midge has several generations per year with two main population peaks; one pre-harvest and one post-harvest, or during active foliar growth periods.

 

Root Weevils

Root weevil larvae feed on roots and can cause damage to roots. Adult weevils feed on foliage and new stems to cause notching of new growth.

Adult black vine weevils, clay colored weevils, and strawberry weevils will be emerging during this period. When weevils first emerge, their bodies have not fully hardened and are quite soft to the touch.

Black vine weevils are up to 1/3” long and are black with a few small yellow or orange spots.

Clay colored weevils are slightly smaller than black vine weevils and are mottled with darker and lighter shades of brown or gray.

Strawberry weevils are 1/5” long and range from black to brown in color.

Other weevil species are present as larvae during this period and may be found in the soil below the plant.

 

Mummyberry

At bloom stage, leaves and blossoms begin to become infected by spores from the mummies on the ground. Infected leaves will flag and turn brown. Infected blossoms turn brown and wither. Environmental factors such as air moisture and prevailing winds contribute to the degree of infection.

 

Godronia Canker

New infections may be forming at this stage at leaf scars and other wounds on stems. Infections are reddish brown and form a bull’s eye pattern.

 

Botrytis

Spores are transmitted under favorable conditions at this time of year, such as high humidity and cool to mild temperatures. Blossoms are susceptible to infection and the pathogen can move from the blighted blossom to the stem and may cause girdling. All growth above the girdling is then killed.

 

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.

 

Blueberry Shock Virus

Shock virus is transmitted by pollinating insects between plants and can spread quickly in a field. Symptoms begin to appear just prior to bloom; affected new tissue appears black and older foliage will turn orange. Foliage and developing flowers will wither. Once a plant is infected, severe yield loss will occur that year. Plants will flush with new growth later in the season. Yield will recover in the following year.

 

Blueberry Scorch Virus

This serious disease can be quickly spread through a field and between fields by aphid transmission. Symptoms are similar to that of blueberry shock virus, but plants will not recover in the following year. Symptoms include twig die-back, complete browning of blossoms and some leaves and eventual stem and plant death. The plant usually retains the scorched blossoms into the fall and sometimes through the following season. Early detection is very important; management depends on minimizing spread of the disease.

 

Anthracnose

Spores are released from infected twigs throughout the growing season and are transmitted to flowers and developing fruit during a rain event. Fruit are susceptible to infection at all stages of development but do not show symptoms until ripening.

 

Voles

Voles resemble house mice; they are 4-5 inches long, and gray or gray-brown in color. They create tunnels in the soil and can feed on fine roots or girdle stems. This tunneling also creates air pockets in the root zone. Vole populations are regulated by food availability and climatic conditions.

 

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.

 

Monitoring

General Guidelines

See general guidelines in the “Introduction” section of the manual.

Aphids

• Check 5 leaves at each plant for aphid nymphs and adults.

• Inspect the undersides of leaves and inside the curled leaves of terminal shoot growth.

• Record the number of leaves with more than 5 aphids per leaf.

Consider treatment:
• When not in a scorch virus area: if 50% of leaves sampled have over 5 aphids per leaf.

• When in a scorch virus area: if 10% of leaves sampled have over 5 aphids per leaf.

 

Wintermoth

• Inspect five flower clusters per plant. Record number of infested or damaged clusters.

• Look for feeding activity such as silk, frass, discolored buds and chewed entrance holes in the sides of buds.

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

• Be cautious of applying pesticides that may disrupt pollinators.

 

Leafrollers (OBLR)

• Place pheromone traps in fields beginning in late April or May and check weekly. Starting one week after peak flight, examine leaves for worm infestation

• Inspect 5 flower clusters per bush at each site.

• Gently pull apart flower clusters and look for larvae and feeding damage.

• Record the number of caterpillars found.

 

Gall Midge

• Begin looking for damage in May.

• Inspect 5 shoots per plant.

• Look for blackened tips of unfolding leaves of the terminal growth and deformed shoots.

• Using a hand lens, inspect the tip for the small maggot, usually located at the stem and leaf junction.

• Record the percent of shoot tip infection to track population trends. No thresholds are currently known. By keeping records of trends you may be able to determine a farm specific threshold.

Management:
If branching like witches broom occurs to a large degree, prune out damaged branches to promote normal bush growth.

 

Root Weevils

• Look for plants with reduced vigor. These may have larval feeding damage on the roots.

• At several places at each site, dig around the soil at the crown of the plant to look for grubs feeding on roots. Record number of grubs found in soil around 10 plants.

• After May, look for notching on lower leaves and new shoots. Record adult feeding damage on a scale of 1-5

• At night, look for adult weevils feeding on foliage by shaking the plant onto a light colored cloth.

• In the day, look for adults in debris and mulch around the base of the plant.

• Consider treatment if plants show signs of low vigor and weevils have been found.

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

 

Mummyberry

• At each bush, inspect 5 shoots for infected leaves.

• Infection will appear as drooping shoots and the upper surface of the leaves will turn brown from the petiole outwards. The brown section of the leaf may be covered in tan-gray fuzz.

• Record percent of shoots that are infected.

• Consider treatment when conidia are present to avoid secondary infection of flowers and fruit clusters.

 

Godronia Canker

• Inspect 20 plants per site.

• Look for infections on current year stems or wounded areas that show up as reddish brown cankers, often with gray centers.

• New cankers may appear as small, reddish discolorations, often around leaf scars.

• Record number of infected plants.

 

Botrytis

• On each plant, examine 5 branch tips for evidence of Botrytis.

• 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. Record number of infected plants.

• Branch tips killed by winter injury are easily infected.

Management:
• Keep an open canopy to increase air circulation.

• Remove infected plant material.

• Avoid excessive use of nitrogen fertilizer in the spring; the Botrytis fungus will readily infect succulent green growth.

• In areas with high levels of infection, a treatment may be made during bloom and fruit ripening

 

Bacterial Blight

• Monitor plants at site for reddish-brown to black cankers

• Send samples to lab for diagnosis.

Management:
• Prune out infected wood immediately.

• Educate farm workers on identification and pruning techniques.

 

Blueberry Shock Virus

• Monitor plants at site for blackening new foliage and flower clusters.

• Tag plants with symptoms and record the location of these plants on your scouting sheet.

• Plants that do not recover from symptoms should be suspect for blueberry scorch virus.

 

Blueberry Scorch Virus

• Monitoring of the plants at each scouting site will be helpful, but plants throughout the field should be noticed and location recorded if symptomatic.

• Symptoms are similar to shock virus symptoms. Blossoms and leaves blight and dry up. Symptoms may be seen on the whole plant or on just one or a few stems of the plant.

• Plants next to infected plants may not show symptoms.

• If scorch virus is suspected, samples should be sent to Oregon State University. See the profile page for Blueberry Scorch Virus for sampling protocol.

Management:
• Plants found with scorch virus should be removed from the field immediately. Bordering plants should be carefully monitored for symptoms.

• There are currently no control measures for this virus.

 

Anthracnose

• Inspect 20 plants per site.

• Look for orange spore masses on last year’s fruit stems. Symptoms are more evident on ripened fruit

• Record number of symptomatic plants.

 

Voles

• Monitor for voles using monitoring stations with apple baits, as described in the profile page.

• Continue monitoring 2-3 weeks following treatment.

 

Birds

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

• Continue monitoring through harvest.

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

• Adapt management plan according to scouting levels

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