Douglas Fir: Aphids

categories: Conifers Douglas Fir Douglas Fir Insects Ornamentals

revision date: 2023-04-04 12:00

Colony of black Giant conifer aphids on branch.
Giant conifer aphids on pine
Photo by: A.L. Antonelli

Biology

The aphids that infest Douglas fir are quite large—up to 1⁄5″ long. They may range in color from gray to brownish to dark. The aphids establish large colonies on the twigs but are rarely found feeding on needles. Large amounts of honeydew (a sticky material) are secreted, often attracting ants. The honeydew may become covered with a dark growth of sooty mold. Aphid feeding on Douglas fir may cause distorted stems or stunted growth.

Management Options

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

Non-chemical Management

Select non-chemical management options as your first choice!

  • Provide proper culture for trees. Healthy plants are able to tolerate large aphid infestations with relatively little damage.
  • Decrease amount of nitrogen available to discourage aphid reproduction. Use a slow-release or lower-nitrogen fertilizer formula.
  • Wash aphids from trees with a strong stream of water.
  • Encourage aphid-eating insects such as ladybird beetles and green lacewings. Avoid using broad-spectrum insecticides which kill these beneficial predators.

Chemical Management

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

  • When making foliar applications, thorough coverage of the foliage is important, including lower leaf surfaces.
  • Follow label instructions for products applied as a drench.
  • Apply if aphids begin to build up.
  • Apply oils in delayed dormant period.
  • 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.