Elm: European elm scale
The European elm scale is a reddish-brown to purplish scale surrounded by a conspicuous fringe of white, waxy material. They sometimes resemble mealybugs. The mature females are about 1/8″ in diameter. The crawlers emerge in late spring and summer and are yellowish to dark brown. The scales feed on twigs and branches as well as leaves, and overwinter as immature crawlers in bark crevices of small branches and branch crotches. Feeding scales produce honeydew, a sweet, sticky material which attracts honeydew-feeding ants and may become covered with a growth of black sooty mold. Infested trees may show yellowing leaves and early leaf drop, followed by death of twigs and branches. Severe infestations may cause extensive damage. The European elm scale feeds only on elms.
Use Integrated Pest Management (IPM) for successful plant problem management.
Select non-chemical management options as your first choice!
- A strong stream of water will wash off some scales. This is most effective in spring, before leaves emerge.
- Provide proper culture to maintain plant health. Healthy trees are more able to tolerate scale infestations.
- Asiatic elms such as Siberian elm (Ulmus pumila) and Chinese elm (U. parvifolia) are apparently not infested.
- Natural enemies such as ladybird beetles and green lacewings help control scale populations. Avoid use of broad-spectrum insecticides which kill beneficial insects.
- Prune and destroy twigs to help control isolated infestations, when practical.
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- Apply to control the immature crawler stage, usually in late spring to early summer.
- Scout for crawlers and gather life history data.
- Oils are effective in early-late spring.
- 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.