Yew: Lecanium scale

• Categories: Conifers Ornamentals Yew Yew Insects
• Last review date: 2025-12-03 10:06

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

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

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

• 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

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.

• All Seasons Horticultural and Dormant Spray Oil Concentrate [Organic]
  Active ingredient: mineral oil
  EPA registration number: 4-80
• R-T-U Year-Round Spray Oil
  Active ingredient: mineral oil
  EPA registration number: 6218-78
• Safer Brand BioNEEM Multi-Purpose Insecticide and Repellent Concentrate [Organic]
  Active ingredient: azadirachtin
  EPA registration number: 70051-6-42697
• Safer Brand Insect Killing Soap Concentrate II [Organic]
  Active ingredient: potassium salts of fatty acid
  EPA registration number: 42697-60
• This list may not include all products registered for this use.