WSU Extension

Hortsense

Plum, Prune (Fresh)
 
Disease
Armillaria root rot 
Bacterial canker 
Black knot 
Brown rot 
Crown gall 
Cytospora canker 
Plum pockets 
Russeting 
Shothole (Coryneum blight) 
Silver leaf 
Virus diseases 
Insect
Aphids 
Apple-and-thorn skeletonizer 
Brown marmorated stink bug 
Earwigs 
Fruittree leafroller 
Leafhoppers 
Pacific flatheaded borer 
Peach twig borer 
Peachtree borer 
Pear slug 
Scale insects 
Shothole borer 
Spider mites 
Spotted wing Drosophila (SWD) 



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Caption: Pear slug and damage
Photo by: R.D. Akre
  
Plum, Prune (Fresh) : Pear slug
(revision date: 3/10/2017)


Biology
The pear sawfly is also known as the pear 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 caterpillar-like larvae are covered with a dark green to black slime which gives them the slug-like appearance. The larvae are yellow immediately after molting 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 (where it is called the cherry slug) 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 Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • 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