WSU Extension

Hortsense

Caption: Cotoneaster webworm damage
Photo by: C.R. Foss
  
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Cotoneaster : Cotoneaster webworm
(revision date: 3/10/2017)


Biology
The cotoneaster webworm is a dark brown caterpillar, 1/4" to 1/2" long. It typically ties clumps of leaves together with webbing and feeds within the nests, skeletonizing leaves. The caterpillars feed during the summer and fall, overwintering in nests on the plant and pupating in the spring. The dark gray, night-flying adult moth emerges in the spring to lay eggs. The webworm is primarily a problem on Cotoneaster horizontalis (rock cotoneaster).
Management Options

Non-Chemical Management
  • Hand-pick and kill caterpillars.
  • Prune out and destroy nests.
  • Remove any overwintering nests found on the plant.
Select non-chemical management options as your first choice!

Chemical Management


Monitor plants and apply product when caterpillars first appear. 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.
  • Bayer Advanced Power Force Multi-Insect Killer R-T-S
    Active ingredient: cyfluthrin  |  EPA reg no: 72155-39
  • Bonide Systemic Insect Control
    Active ingredient: acephate  |  EPA reg no: 239-2461-4
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • 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.
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Caption: Cotoneaster webworm damage
Photo by: C.R. Foss
Caption: Cotoneaster webworm
Photo by: S.J. Collman