WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Pre-Harvest

Biology and Monitoring

 

 
Insects
Diseases
Key Pests
 • Aphids
 • Wintermoth & Spanworm
 • Gall Midge
 • Leafrollers
 • Root Weevils
 • Spotted Wing Drosophila
 • Mummyberry
 • Godronia Canker
 • Botrytis
 • Shock Virus
 • Scorch Virus
 • Anthracnose
 • Alternaria Fruit-Rot
Occasional Pests
 • Symphylans
 • Cherry Fruitworm
 • Bacterial Blight
 • Phomopsis Canker
 • Nematodes

 

Biology

Aphids

Unchecked aphid populations continue to increase. Both winged and wingless forms are produced. The spread of scorch virus is still a concern in affected areas; monitor closely for aphids in areas where scorch virus is present.

 

Wintermoth and Bruce Spanworm

Maturing larvae feed on emerging foliage and developing fruit through June or July. Upon maturing (up to 1 inch long), larvae cease feeding and drop to the soil to pupate.

 

Leafrollers (OBLR)

Leaves may be rolled, chewed and tied together with silk at this time and may be attached to fruit clusters with silk. Leafrollers cause little damage to established plants, but may be a harvest contaminant.

 

Gall Midge

In May and June, adults emerge from their overwintering pupal casing in the soil to oviposit eggs in the terminal growth of new shoots. Hatching larvae then feed in the terminals causing the foliage to curl and deform, sometimes resulting in excessive branching.

 

Root Weevils

Rough strawberry root weevil adults usually emerge in June and July. Other species of root weevils may be present as adults, eggs, or larvae in the soil.

 

Spotted Wing Drosophila

Spotted Wing Drosophila (SWD) is a “vinegar fly” but unlike other vinegar flies, which attack rotting fruit, this fly targets ripening and decaying fruit. Although weather dependent, the flies can be active beginning in April. There may be as many as 10 life cycles in a season with a single life cycle lasting eight to fourteen days. Females insert their ovipositor into the fruit; lay one to three eggs per fruit, 7–16 eggs per day, and more than 300 eggs in their lifetime. Pupation can take place both inside and outside of fruit. The fly thrives at cooler temperatures (68ºF), while decreasing in activity, egg laying and longevity at higher temperatures (above 86ºF). Adults are small flies (less than 1/8 inch) with red eyes and a pale brown thorax and abdomen with black stripes on the abdomen. The most distinguishable trait of the adult is that the males have a black spot towards the tip of each wing.

 

Mummyberry

Fruit will start to show symptoms of infection at this stage. Infected fruit will show white growth in the interior of the fruit. Infected fruit may fall to the ground before healthy berries are harvested. This will become the innoculum for the next year.

 

Godronia Canker

Cankers are evident as reddish brown lesions on the stem.

 

Botrytis

The gray fuzzy mold may be seen on developing berries at this time. Infected twigs and leaves may also be seen.

 

Bacterial Blight

This pathogen enters through wounds in stem tissue. Infection levels increase during wet springs and on stems with winter injury. Only previous season’s canes are affected.

 

Blueberry Shock Virus

Infected plants may start to show new growth at this time. Blighted blossoms may still be on the plant or they may have fallen to the ground.

 

Blueberry Scorch Virus

Plants infected with scorch virus will not be recovering at this point like shock infected plants. Scorch virus can be devastating to a field, destroying all plants in an area in a short period of time. Testing for this virus and plant removal are critical in controlling its spread.

 

Anthracnose

Berries will show symptoms when they are nearing maturity which shows as shriveled sections and orange spore masses. Infected ripe fruit can cause great damage to the entire harvest.

 

Alternaria Fruit-Rot

Infected ripening fruit will show symptoms of caving in on one side with dark gray-green spore growth. Dry fruit may become watery when stored following harvest.

 

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

Follow general guidelines in the “Introduction” section. For each pest below, record pest numbers or symptoms on record sheet.

 

Aphids

• Inspect 5 leaves per plant at each site.

• Examine the undersides of leaves and record the number of leaves with 5 or more aphids.

• Look for aphid predators such as ladybug beetles and lacewings that may be contributing to control of the aphid population.

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

 

Wintermoth and Bruce Spanworm

• Inspect 5 fruit clusters per plant at each location

• Look for webbing and frass in the fruit cluster.

• Record number of clusters infested.

• Consider treatment if 5-10% of fruit clusters are infected.

 

Leafrollers (OBLR)

• Inspect 5 leaves per plant at each site.

• Pull apart rolled leaves to confirm the presence of caterpillars inside.

• Record the number of larvae or damaged leaves found.

 

Gall Midge

• Inspect 5 shoot tips per plant at each site.

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

• Uncurl leaves and inspect the tip for the small maggot. Use a hand lens to identify.

• Record the number of damaged shoot tips or the presence of larvae.

 

Root Weevils

• Inspect 20 plants per site for evidence of adult leaf feeding, which appears as notching on leaves and stems sometimes followed by flagging of stem sections.

• Record adult feeding damage on a scale of 1-5

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

• Treatments should be made when the majority of adults of the predominant species have emerged.

 

Spotted Wing Drosophila

• As soon as fruit begins to ripen place traps in field.

• Using a clear 16oz cup, drill or punch numerous 3/16” to 3/8” holes around the cup for fly entry. Leave a 3-inch space on one side of the container for pouring out vinegar. Add about an inch of apple cider vinegar and place a lid on top. Hang trap from the top wire of the trellis on the cool shady side of the row. Trap should be clear from canopy/fruit with holes exposed so SWD can easily fly in.

• Monitor traps twice per week and record number of adults found. Also monitor for small puncture (oviposition scar) wounds on fruit and soft fruit. Adults are attracted to ripe or ripening fruit.

• Record the number of adults found per trap and the percentage of contaminated fruit.

 

Mummyberry

• Inspect five fruit clusters per plant at each site.

• Look for early “ripening” of fruit, where healthy fruit are green and infected fruit are turning a reddish color.

• Record number of clusters with early “ripening” symptoms.

• Cut open 10 fruit per plant to look for whitish growth inside the berry.

• Record number of infected fruit.

• Treatment is not effective at this stage, but you will be able to determine the disease pressure for the next season.

 

Godronia Canker

• Inspect bushes for infections on stems at wounded areas and leaf scars.

• Cankers appear reddish brown with gray centers, giving a bull’s eye appearance.

• Record number of plants with symptoms.

• Remove and destroy infected stems.

 

Botrytis

• Inspect 20 plants per site for infected shoot tips, seen as brown to black sometimes with black sclerotia near the tip. Record the number of infected plants.

• Inspect five fruit clusters per plant for fuzzy gray mold. Record number of infected fruit clusters.

 

Bacterial Blight

• Inspect plants for blighted tips and cankered twigs.

• Symptoms can resemble those of Scorch Virus and Botrytis blight. Send samples to a diagnostic lab for verification.

Management:
Prune out diseased wood

 

Blueberry Shock Virus

• Plants with shock virus should be recovering at this stage with new growth filling in on the plant. Very little fruit will be produced.

• Record number of symptomatic plants.

• Plants still showing symptoms should be suspected for scorch and tested immediately.

 

Blueberry Scorch Virus

• Monitor for scorch during all crop activities, however, scorch symptoms are less visible after bloom.

• Continue to flag suspected bushes and send samples to Oregon State University to be tested.

 

Anthracnose

• Later in fruit maturity, inspect five fruit clusters per plant at each site.

• Infected mature fruit will show symptoms of sunken, shriveled berries, sometimes with orange regions of sporulation.

• Rate whether the level of infection is low, medium, or high.

• Consider treatment if levels of infection are medium to high, especially if weather is warm and wet.

 

Alternaria Fruit-Rot

• Inspect five fruit clusters per plant at each site.

• Look for a caving-in on one side of a berry as well as a dullish gray spore mass at that area.

• Rate whether the level of infection is low, medium, or high.

• Consider treatment if levels of infection are medium to high.

 

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