WSU Extension


True Fir
Annosus root rot 
Armillaria root rot 
Current-season needle necrosis 
Grovesiella canker 
Interior needle blight 
Needle casts 
Phytophthora root rot 
Rust (Pucciniastrum) 
Rust (Uredinopsis) 
Balsam twig aphid 
Balsam woolly adelgid 
Giant conifer aphids 
Spruce budworm 
Spruce spider mite 

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Caption: Balsam woolly adelgid damage
Photo by: R.S. Byther
True Fir : Balsam woolly adelgid
(revision date: 1/22/2016)

The balsam woolly adelgid feeds on the stems of true firs. White or grayish cotton-like masses, inside which are the purplish-black insects, can be found on the twigs, branches, or trunk. Heavy adelgid infestations may cover the entire trunk. The feeding insects cause the tree to form swollen, knob-like areas at nodes and tips of infested branches. Adelgid infestations weaken trees, cause foliage to become sparse, and can kill trees. This is a serious pest in the forest and the landscape on balsam, grand, subalpine, Pacific silver, and Frasier firs. Balsam fir and subalpine fir are particularly susceptible.
Management Options

Non-Chemical Management
  • Hand-wipe to remove minor infestations when possible.
  • Hose infested trees with strong stream of water to wash off these insects.
  • Ladybird beetles and syrphid fly larvae help control adelgid populations. Avoid use of broad-spectrum insecticides which will kill these important predators.
Select non-chemical management options as your first choice!

Chemical Management

Control must be aimed at "crawlers". In western Washington, this is usually in spring around the end of April to early May. These products are toxic to bees. Do not apply any of the products listed on or near blooming plants. To minimize risk to bees, apply in the evening after bees have stopped foraging for the day. 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.
  • GardenTech Sevin Conc Bug Killer
    Active ingredient: carbaryl  |  EPA reg no: 264-334-71004
  • This list may not include all products registered for this use.

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Caption: Balsam woolly adelgid damage
Photo by: R.S. Byther
Caption: Balsam woolly adelgids
Photo by: A.L. Antonelli