Pest description and crop damage Four species of inchworms may injure blueberries, three of which are native to North America. The fourth, and potentially most serious, is the European winter moth, Operophthera brumata, which was introduced to the PNW in 1958. Adult males are small moths with light brown to tan colored wings which have a hairy appearance. Female moths have reduced wing size and are flightless. The larvae are pale green with a light stripe down their sides, up to 12 mm long. Larvae damage the buds, blooms, leaves, and fruit from March to midsummer. Symptoms of leaf feeding are distinct from leafroller larvae: leaves are tied together with silken threads, but not rolled like a leafroller.
Biology and life history This insect pupates in the soil in summer and fall; adults emerge in late fall and early winter (hence the name "winter moth"). After emergence, the flightless female mates, crawls up the canes, and deposits eggs in bud or cane crevices. Larvae hatch in early spring and immediately begin feeding on developing buds. After feeding for several weeks, larvae drop to the soil on silken threads and pupate until fall. Adults emerge after the first frost. There is one generation per year.
Sampling and thresholds Monitor fields in early spring for larvae, larval webbing, and feeding on buds. Also, in early morning and early evening, silken webs may be seen in the slanting sunlight (young larvae climb out to an open branch and send out a fine, silken web for dispersion by wind to find new food sources). A treatment application may be necessary if there are more than eight larvae per plant.
General predators such as lacewings, assassin bugs, and spiders feed on the larvae, but populations are not well regulated by these predators. Cold winter temperature may play a bigger role in controlling populations.
Home gardeners: Pick larvae when you find them, and prune out infested growth.
Management-chemical control: HOME USE
No products are registered for control of this pest in the home garden.
Management-chemical control: COMMERCIAL USE
- acetamiprid (Assail) at 0.085 to 0.1 lb ai/a. PHI 1 day. Do not exceed 0.5 lb ai/a per season.
- Bacillus thuringiensis (Bt) (several brands)-Consult label for rate. PHI 0 days. OMRI-listed for organic use.
- bifenthrin (Brigade and other brands) at 0.033 to 0.1 lb ai/a. PHI 1 day.
- chlorantraniliprole (Altacor) at 0.066 to 0.099 lb ai/a. PHI 1 day.
- diazinon (several brands) at 0.5 lb ai/a. PHI 7 days. One application per season allowed; as such, consider other pests that may need to be managed with diazinon. Restricted use pesticide.
- horticultural oil (several brands)-Consult label for rate. When oil is used for lecanium scale suppression in the dormant season, winter moth eggs on the plants may also be controlled. Some formulations are OMRI-listed for organic use.
- indoxacarb (Avaunt) at 0.65 to 0.11 lb ai/a. PHI 7 days.
- methomyl (Lannate) at 0.45 to 0.9 lb ai/a. PHI 3 days. Do not use during bloom. Restricted use pesticide.
- methoxyfenozide (Intrepid 2F) at 0.25 lb ai/a. PHI 7 days. Begin applications when first signs of feeding damage appear, usually on buds in late winter or early spring. Do not exceed three applications per season.
- novaluron (Rimon 0.83EC) at 0.13 to 0.19 lb ai/a. PHI 8 days. Apply when larvae are young and small, just after egg hatch.
- spinetoram (Delegate WG) at 0.05 to 0.09 lb ai/a. PHI 3 days.
- spinosad (Entrust) at 0.062 to 0.09 lb ai/a. PHI 3 days. Apply at egg hatch or to small larvae. Entrust is approved for organic production. SLN 24(c) OR-160013 and WA-140014 for Entrust SC formulation allow a 1-day PHI in Washington and Oregon only.
- tebufenozide (Confirm 2F) at 0.25 lb ai/a. PHI 14 days. Begin applications when first signs of feeding damage appear, usually on buds in late winter or early spring. Do not exceed 64 fl oz product/a per season.
- zeta-cypermethrin (Mustang) at 0.05 lb ai/a. PHI 1 day. Restricted use pesticide.