San Jose scale is an armored (hard) scale found on many deciduous trees and shrubs including apple, cherry, elm, maple, poplar, and willow. The scale insects are about 1/16" in diameter. The female is gray with a yellow spot in the center. The yellow crawlers are easily spread by wind, birds, or people. San Jose scale may be found on twigs, branches, leaves, and fruit. Heavily infested branches or entire trees may wilt and appear water-stressed. Severe infestations can cause twigs and branches to die back. Repeated infestations can kill trees. Infested fruit develops sunken spots surrounded by reddish areas. The scale overwinters as black immature scales on the bark.

Management Options

Non-Chemical Management

Provide proper plant care. Healthy plants are more tolerant of insect damage.
Prune and destroy localized infestations, when practical.
Natural predators and parasites help control scale populations, but may not prevent damage in severe infestations. Avoid use of broad-spectrum insecticides which kill beneficial insects.
By late April, begin monitoring for crawlers by using double-sided sticky tape.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Apply oil alone or with 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.

Hi-Yield Dormant Spray
Active ingredient: oil/pet distillate | EPA reg no: 7401-428
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.

Images

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Caption: San Jose scale Photo by: K. Grey

WSU Extension

Hortsense