Douglas Fir: Aphids

• Categories: Conifers Douglas Fir Douglas Fir Insects Ornamentals
• Last review date: 2026-04-26 10:31

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

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!

• 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 honeydew.

Chemical Management

• 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

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.