Northwest berry Foundation

Management Detail

Winter Moth/Bruce Spanworm

in Blueberries

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Latin name: Operophtera brumata, O. bruceata


Reason for Concern:
1) Winter Moth and Blueberry Spanworm are major early season pests. Larvae bore into and feed on developing buds.
2) Destruction of the flower buds leads to greatly diminished harvest on fruit crops.
3) They chew on new growth, tie leaves with silken threads, and feed on mature flowers and fruit.
4) Severe infestations, if not controlled, can cause total defoliation.

Eggs, light green at first, later changing to bright orange, are laid in bark crevices. Prior to hatching in early spring, they become very dark. After hatch, larvae initially feed by mining developing buds, leaving holes in leaves, which become conspicuous as the leaves expand. After leaf buds open, the small caterpillars can be found within the tight clusters of new leaves during the day. Larvae of both species are stout-bodied, hairless loopers, with 3 pairs of legs behind the head and 2 pairs of prolegs in the rear. They arch their body when moving along a branch. The larvae are about 1/8-inch long when young and ¾-inch long when fully grown. Young Blueberry Spanworm larvae are dark in color, having blackish heads and dark gray bodies with 3 whitish bands along each side. Fully grown larvae are yellowish-orange with rows of black spots that look like continuous black strips running the length of the body. Spanworm larvae often appear on plants in large numbers at night. During the day, shelter in the litter at the base of the plants. Winter moth larvae have a green body, a narrow, dark green mid-dorsal line, and 3 creamy yellow stripes along each side. Adults are drab gray or gray-brown moths and the 2 species are almost identical in appearance and habits. Females (rarely seen) are 0.6 to 0.8 cm long and have only vestigial wings. Males are light brown, slender-bodied moths with bluish gray wings with brownish markings most noticeable on the veins, and a wingspan of 2.5 to 3.0 cm. All 4 wings are fringed with small elongate scales that give the hind margins a hairy or fringed appearance. Adults are evident from late October to the end of January, often in weedy areas or windbreaks.

Winter Moth females lay overwintering eggs in early winter in bark crevices, while Spanworms tend to lay eggs in litter at the base of the plant. Eggs are deposited singly or in clusters. After mating and egg laying, adult moths die. Egg hatch occurs just at or right before bud break. Some of the newly hatched larvae crawl up tree trunks and produce a strand of silk, which makes them air buoyant. They may also use the silken strand to drop to the ground to hide in leaf litter during the day. At night they crawl back up the plant to feed on buds, foliage, flowers and fruit. In June or July, when larvae are full-grown, they stop feeding and drop to the ground to pupate in the soil. Adult moths begin to emerge about 2 weeks later. There is 1 generation per year.



  • The male flight takes place in November and December. A pheromone to monitor this flight is available only from a source in Eastern Europe.
  • Watch for single strands of spider web-like threads appearing in the branches in late February to March that comes from newly hatched larvae.
  • In early spring, closely monitor flower buds, clusters, and leaves for evidence of feeding and/or larval presence. Larvae are light to dark green caterpillars with two distinct white lines running the length of their bodies. Much larger than leafroller larvae, they react much less when agitated.
  • In fields with a history of winter moth problems, a late winter dormant oil and insecticide tank mix is often used to prevent reoccurrence of the damage.

Cultural Controls:

  • Trim trees around field borders, as trees are also a preferred habitat of the winter moth and spanworm. They also scout in early spring for evidence of larvae and/or larval feeding. A pheromone for the male moth has been identified and shown to be an effective monitoring tool, but is not readily available.


For information about chemical controls, check with our Pesticide Guide.


Winter moth larva - photo by T. Peerbolt


Winter moth damage - photo by T. Peerbolt

Winter moth larva - photo by T. Peerbolt


Winter moth adult - photo by J. Troubridge

Bruce spanworm adult - photo by J. Troubridge

Bruce spanworm larva - photo by J. Troubridge, AAFC

Winter moth damage - photo by T. Peerbolt

Dead blossoms in blueberries and winter moth larvae that caused the damage - photo by T. Peerbolt

Damage done by winter moth - photo by T. Peerbolt


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