Yew: Lecanium scale

categories: Conifers Ornamentals Yew Yew Insects

revision date: 2023-04-04 12:00

Yellow pencil pointing to Lecanium cales on twig shown on a black background.
Lecanium scales on twig
Photo by: R.S. Byther

Biology

Lecanium scales are shiny brown insects found on leaves and twigs. Adults are 1⁄8″-1⁄4″ in diameter and roughly turtle-shaped. Crawlers (immature scales) are flatter. Scales produce large amounts of honeydew, a sweet, sticky material which may attract ants or become covered with a heavy growth of dark sooty mold. Heavily infested plants may appear yellowish or wilted, or show other signs of stress. New growth may be stunted. Lecanium scale is a common pest in the landscape, infesting many plants including dogwood, maple, rhododendron, willow, and fruit trees.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • Natural enemies such as ladybird beetles and green lacewings help control scale populations. Avoid use of broad-spectrum insecticides which kill these and other beneficial insects.
  • Hand-wipe to help control minor infestations.
  • Prune and destroy heavily infested branches, when practical.

Chemical Management

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

  • 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.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.