WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Pre-Bloom

Biology and Monitoring

 

 
Insects
Diseases
Key Pests
 • Aphids
 • Wintermoth & Spanworm

 • Mummyberry
 • Godronia Canker
 • Botrytis
 • Bacterial Blight
 • Shock Virus

Occasional Pests
 • Leafrollers
 • Root Weevils
 • Yellowjackets
 • Phytophthora
 • Anthracnose
 • Tomato Ringspot

 

Biology

Aphids

Aphids begin to emerge from overwintered eggs in the spring and females give live birth. Populations will increase in an unchecked environment; beneficial insects are often present in sufficient numbers to discourage high infestation levels, especially later in the season.

Aphids feed with their piercing-sucking mouthparts on succulent new growth. This can cause deformation of plant tissue and defoliation. High infestations can reduce fruiting bud formation for the following year. Aphids may be found in colonies on the undersides of leaves and in new, curled leaves.

Aphids are also the vectors of viruses, such as Blueberry Scorch Virus (BlSV). In areas with BlSV, monitoring and management of aphids is essential to control this virus.

 

Wintermoth and Bruce Spanworm

Eggs hatch in March and April, which often coincides with bud break of flowers and leaves. Larvae can disperse by ballooning in the wind on silken threads. Blueberry fields bordered by trees and shrubs are often infested by ballooning larvae from other hosts. Larvae are green inchworms (up to 1” in length) with 2 yellow or white stripes running the length of the body.

 

Mummyberry

Mummyberry affects shoots, flower clusters, and fruit. Fruit infection results in unmarketable fruit and can reduce yield by over 50% in susceptible varieties if not controlled. In late February or early March, the small mushroom-like spore cup emerges from infected berries on the soil surface. Spores are released and spread by wind currents to infect leaves and flowers, causing flowers to brown and stems to blacken.

 

Godronia Canker / Fusicoccum Canker

Godronia (asexual form is Fusicoccum) canker infects and causes dieback of new stem tissue. This fungal disease overwinters in infected stems. Conidia produced in the spring are released during wet periods and spread through splashing rain. New infections occur at leaf scars and other openings on the bark of new growing tissue. Infections form a bull’s eye pattern. Large cankers can girdle stems and cause flagging. Most cankers are near ground level, but some occur as high as 3 feet above the ground.

 

Botrytis

Botrytis overwinters in infected stems of bushes and plant debris. Branch tips killed by winter injury are easily infected. Spores are produced during wet spring months and are dispersed through wind movement and water splashes. Damaged leaves and blossoms are vulnerable to Botrytis infection. Infected tissue may appear blighted or be covered in a gray fuzzy mold.

 

Bacterial Blight / Canker

Pseudomonas bacterial blight is a bacteria naturally present in the environment that becomes a problem if it manages to enter plant tissue. Infection occurs only on previous season’s growth. Symptomatic tissue turns a reddish brown color; buds in this region will die. It is a problem during early to late spring, especially if late frosts are prevalent.

 

Blueberry Shock Virus (BlShV)

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 and yields will recover in the following year.

 

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.

 

Monitoring

General Guidelines

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

Aphids

• At each site, visit 20 bushes and inspect 5 leaves for aphid populations.

• Examine the undersides of leaves and inside the curled leaves of terminal shoot growth. Record the number of leaves with over 6 aphids.

• Low numbers of aphids will not cause economic damage. Beneficial insects should keep this pest in check.

Note: If Blueberry Scorch Virus is present, intensive aphid control is required. One critical period of monitoring and treatment is early in the season when winged aphids are present. Winged aphids will spread the disease through a field and between fields.

 

Wintermoth and Bruce Spanworm

• Inspect 5 shoot tips per plant for wintermoth and Bruce spanworm. Record number of buds infested or showing feeding damage.

• Evidence of feeding activity includes silk, frass, discolored buds, chewed entrance holes in the sides of buds.

• Consider treatment if 5-10% of bushes have infested buds. Insecticide treatments should be scheduled to target the hatching larvae; insecticides are less effective once larvae have entered the bud or flower.

 

Mummyberry

• Scrutinize the soil at the base of 20 plants per site.

• In February: rake the soil and look for fallen mummified berries. Open berries and look for the developing spore cup which appears like a germinating seed. Record the level of mummyberry found (none, low, medium, high)

• In March: monitor for mushroom-like spore cups on the soil surface. Peak spore production usually occurs shortly after bud break. Record the level of spore cups found (none, low, medium, high)

• Once green foliage develops, scout for primary infection on the leaves, which shows as a blackening in the center of the leaf. The leaves will wilt quickly and the twig tips will bend. Look for grayish green tufts of fungus associated with the wilted foliage and blackened stems.

Management:
• Prior to budbreak, shallow cultivation, less than one inch deep, will prevent spore cup development, but will not be effective is sawdust mulch is used.

• Mummies can be covered with soil or mulch at least 2 inches deep.

• Avoid wet sites and overhead irrigation at least until petal fall and try to improve drainage.

• Select resistant cultivars, if available. Late flowering cultivars are often able to avoid infection.

• Consider treatment if spore cups are found at 10-20% of bushes and weather conditions are wet and above 50°F.

 

Godronia Canker

• Inspect several stems per plant for evidence of cankers. Record the number of plants showing symptoms.

• Cankers are seen as small reddish-brown blemishes in early spring.

• This disease is spread through wet weather in the spring; early treatment is important to reduce infection.

Management:
Infected stems should be pruned from the plant and destroyed.

 

Botrytis

• Examine 5 branch tips per plant for evidence of Botrytis.

• Look for branch tips that are grayish and brittle or dried-up. Record number of plants showing symptoms.

• Branch tips killed by winter injury are easily infected.

Management:
• 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 / Canker

• At each plant, look for blighted tips or cankered twigs, especially when frost has occurred. Record number of plants showing symptoms.

• Symptoms are similar to Blueberry Scorch Virus and Botrytis mold. Send samples to be tested if unsure.

Management:
Prune out diseased wood as soon as possible.

 

Blueberry Shock Virus

• Regularly monitor for shock just prior to bloom.

• Visit 20 bushes at each site. Record the number of plants that exhibit symptoms and tag these plants.

• Also, monitor throughout the field for symptoms. Tag suspected plants and have them tested.

• Blueberry shock virus symptoms are very similar to blueberry scorch virus, so have suspected plants tested immediately. Testing is done at USDA-ARS in Corvallis Oregon for a small fee. Contact your extension office for more information on testing. Sampling information is included in the profile pages for scorch virus.

• At this stage, symptoms are flowers and new leaves unexpectedly dying. Often just a branch will show symptoms, but sometimes the whole plant will show symptoms.

Management:
• Certified new stock should be used.

• Do not plant a new field next to an infected field.

• If in larger fields with an isolated area of the disease, rogue out the diseased plants. Otherwise, let the disease run it’s course.

 

Voles

• Spring monitoring is done to assess winter mortality and new populations.

• Monitoring stations can be constructed using a protected shelter to cover a runway or tunnel entrance. Shelters can be constructed using roofing shingles or PVC piping. Place an apple wedge as bait underneath the shelter. Check the apple bait every 24 hours for 2-3 days. Inspect the apple wedge for feeding damage. Four to eight bait stations per acre can provide an accurate assessment of vole populations.

• Monitor again 2-3 weeks following treatment to determine efficacy.

Management:
•Treatment threshold ranges from 20-40% positive from monitoring station.

• Habitats can be changed to reduce vole problems

• Remove debris piles

• Regularly mow field margins and keep large weeds under control

• Pelletized baits can be broadcast, but they degrade quickly.

• Bait stations can be made by making a T out of 2-3 inch PVC pipe filled with bait. (see profile page for more information)

 

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