WSU Extension


Douglas Fir
Armillaria root rot 
Laminated root rot 
Rhabdocline needle cast 
Stem cankers 
Swiss needle cast 
Upper stem canker 
Yellow-green mottle syndrome 
Cooley spruce gall adelgid 
Douglas fir needle midge 
Douglas fir tussock moth 
Douglas fir twig weevil 
Sequoia pitch moth 
Silverspotted tiger moth 
Spruce spider mite 

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Caption: Giant conifer aphids on pine
Photo by: A.L. Antonelli
Douglas Fir : Aphids
(revision date: 2/14/2019)

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

Non-Chemical Management
  • 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.
Select non-chemical management options as your first choice!

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.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • All Seasons Horticultural & Dormant Spray Oil Conc [Organic]
    Active ingredient: oil/pet distillate  |  EPA reg no: 4-80
  • Bonide Systemic Insect Control
    Active ingredient: acephate  |  EPA reg no: 239-2461-4
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.

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Caption: Giant conifer aphids on pine
Photo by: A.L. Antonelli