WSU Extension


Bacterial twig blight 
Marssonina leaf & twig spot 
Twig blight (Venturia) 
Poplar-and-willow borer 
Satin moth 
Spiny elm caterpillar 

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Caption: Satin moth
Photo by: A.L. Antonelli
Willow : Satin moth
(revision date: 6/29/2015)

The caterpillars of the satin moth feed on leaves of willows and poplars. They may also occasionally attack oak and aspen. The adult moth is satiny and pure white, with a wingspan of 1 1/2" to 2". The caterpillars are voracious feeders, sometimes causing severe defoliation of trees. Mature caterpillars are approximately 2" long. They are black, with red and white patches and tufts of hairs along the sides.
Management Options

Non-Chemical Management
  • Hand-pick caterpillars when practical. Wear gloves, as hairs may irritate the skin.
  • Natural enemies, including a fly and several parasites, help control satin moth populations. Avoid use of broad-spectrum insecticides which may kill beneficial insects.
Select non-chemical management options as your first choice!

Chemical Management

Applications should only be made if defoliation begins to approach 25% of the canopy. 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.

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Caption: Satin moth
Photo by: A.L. Antonelli