WSU Extension


Crown gall 
European canker (Nectria canker) 
Fire blight 
Pacific Coast pear rust 
Pear trellis rust 
Powdery mildew 
Pseudomonas blossom blast and dieback 
Stony pit 
Virus diseases 
Apple-and-thorn skeletonizer 
Brown marmorated stink bug 
Codling moth 
Cutworms and armyworms 
Pear psylla 
Pear slug (pear sawfly) 
Pearleaf blister mite 
San Jose scale 
Spider mites 

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Caption: Pearleaf blister mite damage
Photo by: C.R. Foss
Pear : Pearleaf blister mite
(revision date: 2/14/2019)

Pearleaf blister mites are tiny, white to yellowish eriophyid mites that feed on leaves and fruit. Damage on leaves is caused by mites feeding inside the leaf tissues, resulting in the formation of pale green to reddish blistered areas on the leaf. Later in the summer these blistered areas will turn brown to black as the leaf tissue dies. Leaf blisters are typically 1/8" to 1/4" in diameter. Severe blister mite infestations can cause leaves to drop. Blister mite damage to fruit consists of russetted, somewhat sunken areas on the skin. These mites overwinter under bud scales, attacking emerging leaves in the spring. Severely infested buds can fail to develop in the spring.
Management Options

Non-Chemical Management
  • Predatory mites help control populations by feeding on exposed mites. They cannot attack mites inside blisters. Avoid use of broad-spectrum insecticides which kill predatory mites and beneficial insects.
  • Removing and destroying infested leaves may help control mite populations on small trees.
  • Provide proper culture. Healthy trees easily tolerate some insect damage and leaf loss. Neglected trees are more likely to be attacked.
Select non-chemical management options as your first choice!

Chemical Management

Apply oil plus lime-sulfur in early spring just prior to bud swell. 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.
  • All Seasons Horticultural & Dormant Spray Oil Conc [Organic]
    Active ingredient: oil/pet distillate  |  EPA reg no: 4-80
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • This list may not include all products registered for this use.

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Caption: Pearleaf blister mite damage
Photo by: C.R. Foss