WSU Extension

Hortsense

Oak : Pit scale
(revision date: 2/14/2019)


Biology
Pit scales of oak may be brown, gold, or greenish in color. They feed on twigs and small branches, with young wood most commonly infested. Pit scale feeding causes the tissue of the twig to swell around the insect. The growth makes the scale appear to be in a pit on the bark. Numerous scales on a twig cause it to appear roughened. Adult scales are covered with a hard shell and are about 1/16" in diameter. Severe infestations cause twig dieback. Heavy infestations of pit scale combined with drought stress or anthracnose, a fungal disease can result in severe weakening or death of trees.
Management Options

Non-Chemical Management
  • Prune out and destroy severely infested twigs to help control localized infestations (when practical).
  • Provide proper culture. Healthy trees are more able to tolerate insect damage and are more disease-resistant.
  • Natural enemies may help control scale populations. Avoid use of broad-spectrum insecticides which kill beneficial insects.
Select non-chemical management options as your first choice!

Chemical Management

Apply to control the immature crawler stage, usually in late spring to early summer. 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
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • 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.
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Caption: Oak pit scale
Photo by: A.L. Antonelli