WSU Extension

Hortsense

Cherry : Pear slug (Cherry slug)
(revision date: 3/10/2017)


Biology
The pear sawfly is also known as the pear slug or cherry slug because of its resemblance to a small, dark slug. These insects are the larval stage of a glossy black sawfly about 1/5" long. The larvae are covered with a dark green to black slime which gives them the slug-like appearance. The caterpillar-like larvae are yellow immediately after molting and until the slime is produced. Larvae are also yellow-orange immediately before pupating. Pear slugs feed on upper leaf surfaces, skeletonizing leaves. Severe infestations can cause defoliation, weaken trees, and affect fruit development. The pear slug prefers cherry and pear, but will also feed on plum.
Management Options

Non-Chemical Management
  • Natural enemies control pear slug populations fairly effectively. Avoid use of broad-spectrum insecticides which can kill beneficial insects.
  • Wash pear slugs from trees with a strong stream of water.
  • Hand removal is effective on small trees.
Select non-chemical management options as your first choice!

Chemical Management

Chemical control measures are rarely necessary except for very severe infestations. Apply when larval damage approaches 25% defoliation. NOTE: Esfenvalerate is toxic to bees. Do not apply products containing esfenvalerate on or near blooming plants. To minimize risk to bees, apply in the evening after bees have stopped foraging for the day. 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.
  • Monterey Bug Buster II
    Active ingredient: esfenvalerate  |  EPA reg no: 1021-1778-54705
  • Safer Brand Insect Killing Soap with Seaweed Extract II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-59
  • This list may not include all products registered for this use.
Images
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Caption: Pear slug and damage
Photo by: R.D. Akre