WSU Extension

Hortsense

Oak : Western oak looper
(revision date: 4/20/2015)


Biology
The Western oak looper feeds mainly on the foliage of the Oregon white (or Garry) oak (Quercus garryana). Mature larvae of the Western oak looper are about 1" long and light brown with black spots when mature. They move in a characteristic "looping" or measuring-worm fashion. The adult moth is yellowish to dark brown. Severe infestations are rare, but can result in almost total defoliation of trees. No permanent damage is done by occasional outbreaks.
Management Options

Non-Chemical Management
  • Severe outbreaks seldom occur.
  • Provide proper culture. Healthy trees can better tolerate insect damage.
  • Hand-pick caterpillars when practical.
Select non-chemical management options as your first choice!

Chemical Management

Apply in July, or early August when larvae are feeding. It is mostly a pest in Oregon. If Bt is chosen, be sure to apply when insect is feeding. Best time is when caterpillars are young. Use a spreader-sticker with liquid Bt formulations. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Safer Brand Caterpillar Killer for Trees, Shrubs & Vegetables Conc II [Organic]
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 70051-106-42697
  • Safer Brand Caterpillar Killer/Trees, Shrubs, & Vegetables Conc
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 42697-23
  • This list may not include all products registered for this use.
Images
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Caption: Looper on rhododendron
Photo by: S.J. Collman