Elm: Aphids

categories: Elm Elm Insects Ornamental trees Ornamentals

revision date: 2023-04-04 12:00

Curled leaf with aphid on black background.
Elm woolly aphid
Photo by: A.L. Antonelli

Biology

Aphids are soft-bodied, pear-shaped insects that feed on the leaves. They are yellowish to green in color and approximately 1/16″ long. Aphids often produce honeydew, a sweet, sticky substance which can develop a dark growth of black sooty mold. Deformed leaves are often associated with heavy infestations. Whitish cast skins are often found on leaves, as well. Some aphid species may also cause galls.

Management Options

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

Non-chemical Management

Select non-chemical management options as your first choice!

  • Hand-wipe or prune to control small, localized infestations when practical.
  • Wash aphids from foliage with a strong stream of water.
  • Encourage natural predators including ladybird beetles, lacewings, syrphid (hover) fly larvae, and predatory wasps. Avoid use of broad-spectrum insecticides which kill these beneficial insects.
  • Control honeydew-feeding ants, which may protect aphid colonies from predators.
  • Provide proper nutrition. High levels of nitrogen in the foliage encourage aphid reproduction. Switch to a slow-release or low-nitrogen fertilizer.

Chemical Management

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

  • Thorough coverage of the foliage is important, including lower leaf surfaces.
  • Apply when aphid build up is noticed.
  • Apply oils in early spring before bud swell.
  • 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.