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Caption: Lecanium scales
Photo by: R.S. Byther
Hawthorn : Scale insects
(revision date: 2/14/2019)

Several species of scales may be found on hawthorn. In general, scales are approximately 1/16" to 1/8" in diameter, dull or shiny, and grayish to dark in color. They are typically found on the bark of small twigs and sometimes on the lower surfaces of leaves. They are flattened, circular to oval or oyster-shaped in outline, and may be hard-shelled or relatively soft. The immature scales (crawlers) are usually yellowish to brown and soft-bodied. They may be found on leaves or twigs and are typically present in early summer, depending on species. Scale-infested plants may show signs of wilt, leaf yellowing, and/or premature leaf drop. Heavily infested branches may be killed. Honeydew, a sweet, sticky material, may be present as a result of scale feeding and may become covered with a growth of black sooty mold.
Management Options

Non-Chemical Management
  • Provide proper culture. Healthy plants are more able to tolerate damage.
  • Natural enemies such as ladybird beetles and parasitic wasps may help control scale populations. Avoid use of broad-spectrum insecticides which kill these beneficial insects.
  • Prune out and destroy isolated infestations and heavily infested branches, when practical.
  • In minor infestations, it may be possible to hand-wipe branches to reduce numbers of scales.
Select non-chemical management options as your first choice!

Chemical Management

Scout for crawlers. Oils are effective in very early spring in controlling lecanium, San Jose, and brown scales, but not oystershell scale. All products excluding oils: 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
  • 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: Lecanium scales
Photo by: R.S. Byther
Caption: Oystershell scales
Photo by: Unknown
Caption: San Jose scale
Photo by: K. Grey