WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Winter Moth & Bruce Spanworm

Insects & Invertebrates

 

Winter Moth and Bruce Spanworm

 

Symptoms

Unmanaged, winter moth larvae and span worms can cause significant yield loss in blueberries. Larvae feed on flower buds, flowers and foliage and can contaminate harvested berries. Damage is seen as small tunnel holes on buds.

 

Identification

Adult male moths are mottled brown and gray with lighter gray underwings. Female moths are wingles and are rarely seen.

Winter Moth Larva and Bruce Spanworm Larva

Larvae are pale green with three white stripes developing on each side as larvae grow. Head capsules of the winter moth are also pale green while Bruce spanworms begin with dark head capsules and can lighten to pale green upon developing. Mature larvae are up to 1 inch long. Larvae can be distinguished from other types of caterpillars by typical ‘inchworm’ or looper movements.

 

Life History

Adult moths begin mating in November and continue until early January. Female moths can be found climbing blueberry canes in the evening to call for males. Females deposit eggs in cracks and crevices in the bark surface of blueberries. Eggs hatch in March and April often coinciding with bud break of flowers and leaves.

After egg hatch, larvae can disperse by ballooning in the wind on silken threads. Blueberry fields bordered by trees and shrubs often are infested by ballooning larvae from these other hosts.

Larvae prefer to feed on flower buds. Larvae tunnel into the bud and begin feeding on the developing flower parts and buds. During bloom, larvae can be found inside the flower. Maturing larvae feed on emerging foliage and developing fruit through June or July. Upon maturing, larvae cease feeding and drop to the soil to pupate. There is one generation per year.

 

Monitoring

Pheromones are commercially available for monitoring adult flight. Due to the difficulty of synthesizing the winter moth/spanworm pheromones, purchasing from a reliable source can be difficult. Contact your local agricultural supplier or county extension agent for assistance in finding a commercial supplier for winter moth/spanworm pheromones.

Begin monitoring egg hatch and larval feeding in March or just prior to bud break. Inspect buds for silk and frass. Inspect buds for feeding damage and small holes along the side of the bud.

Open suspect buds to find the feeding larvae. Inspect five flower buds or flower clusters per blueberry bush. Winter moth and spanworm infestations will appear in the field in patches. Infestations along borders may be uniform due to ballooning larvae in the early spring. Monitor field edges, especially those bordering deciduous trees and shrubs, alternate hosts of winter moth and spanworm.

 

Thresholds and Management

Insecticides properly timed can reduce winter moth and spanworm problems. Time insecticide applications to target the hatching larvae. Once larvae have entered the bud or flower, insecticides can be less effective. Use an insecticide that is soft on predators such as Bacillus thuringiensis. Do not apply insecticides during bloom that will kill or disrupt pollinators.

 

Resources

Oregon State University, Joe DeFrancesco, Gina Koskela and Glenn Fisher; Control of Winter Moth (Operophtera brumata, L.) in PNW Blueberries
http://www.ipmnet.org/Joe/Winter%20Moth%20in%20PNW%20Blueberries.pdf

Washington State University Extension, Glenn Fisher, Arthur Antonelli, and Carrie Foss. Winter Moth: A Key Pest of Blueberries in the Pacific Northwest
http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls75wintermoth.pdf

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