WSU Extension

Hortsense

Common Insects & Mites : Lecanium scale
(revision date: 4/14/2015)


Biology
Lecanium scales are a complex of scale species ranging from variously mottled to all brown. The mature female scales look like bumps on twigs, while the mature males are flat, somewhat oval discs. First noticeable in late spring when eggs and tiny crawlers are produced. The crawlers appear on the underside of leaves throughout much of the summer. They feed on a wide variety of trees and shrubs. When populations are high, they produce an abundance of honeydew, a shiny, sticky, sweet substance which can accumulate on leaves and other surfaces beneath infested plants. Honeydew may attract ants or serve as a food source for sooty mold, a black fungus which is unsightly but does not directly harm plants.
Management Options

Non-Chemical Management
  • If the infestation is minor, scales may be wiped from the bark or leaves.
  • Natural predators such as ladybird beetles and green lacewings may greatly reduce the number of crawlers.
  • Prune and destroy heavily infested branches, if practical.
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 crawler stage, usually in late spring to early summer. Make certain that the product you purchase is labeled for the target host and carefully read and follow label instructions.

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Caption: Lecanium scales
Photo by: R.S. Byther
Caption: Lecanium scales
Photo by: R.S. Byther