WSU Extension


Birch leafminer 
Bronze birch borer 
Oystershell scale 

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Caption: Oystershell scales
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Birch : Oystershell scale
(revision date: 2/14/2019)

Oystershell scale insects are found on trunks, branches, and twigs of many broadleaved deciduous plants. They occur less frequently on the leaves and other plant parts. The mature scale is approximately 1/8" long, hard-shelled, brownish or gray in color, and usually elongated like an oyster or mussel shell. Scale infestations are often initially limited to isolated colonies on single branches or twigs. Infested plants may show off-color foliage. Oystershell scales overwinter as eggs beneath the shell of the female scale, then hatch and move to feeding sites in late spring or early summer. Scales are spread from plant to plant by birds, people, wind, or insects.
Management Options

Non-Chemical Management
  • In minor infestations it may be possible to pick scales off branches.
  • Where practical, prune and destroy heavily infested branches.
  • Natural predators and parasites help control scale populations, but usually not soon enough to prevent damage to plants.
Select non-chemical management options as your first choice!

Chemical Management

Scout for crawlers. Insecticide applications can be effective when applied to control the immature crawlers stage, usually in late spring to early summer. Oils are effective in the delayed dormant period. Use superior type oil sprays only on overwintering nymphs. 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.
  • Bonide Systemic Insect Control
    Active ingredient: acephate  |  EPA reg no: 239-2461-4
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • 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: Oystershell scales
Photo by: Unknown