Rhododendron: Lecanium scale

categories: Ornamentals Rhododendron Rhododendron Insects Shrubs

revision date: 2024-06-05 02:08

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


Lecanium scale adults are found on the twigs in late spring. At this stage they are usually brown or mottled brown and white bumps on the stems. During the summer and fall, scale nymphs can be found on the foliage and are flat and light brown. The partially developed nymphs overwinter in crevices in the bark.

Management Options

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

Non-chemical Management

Select non-chemical management options as your first choice!

  • Prune to remove heavily infested branches.
  • Hand removal of adult scales (when practical) can reduce populations to tolerable levels.
  • Keep dust down and plant flowering plants to attract natural predators such as ladybird beetles.
  • Provide proper nutrition for plants. High levels of nitrogen in the foliage may encourage scale reproduction. If necessary, switch to a slow-release formula or one with less nitrogen.

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.
  • 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.