WSU Extension


Annosus root rot 
Phytophthora root rot 
Hemlock scale 
Hemlock woolly adelgid 

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Caption: Hemlock woolly adelgid
Photo by: R.S. Byther
Hemlock : Hemlock woolly adelgid
(revision date: 3/10/2017)

Hemlock adelgids are aphid-like insects. They appear as white, woolly tufts on the bark and needles. Trees with severe infestations may be stressed, predisposing them to other insect and disease problems. Needles drop prematurely, weakening the tree and sometimes leading to death. The adelgid overwinters as woolly adults, with reddish-brown crawlers similar to scale crawlers appearing in spring and early summer. Adults are black beneath the woolly material. Hemlock adelgids are sometimes known as hemlock chermes. The hemlock adelgid is especially a problem on hemlock hedges.
Management Options

Non-Chemical Management
  • Western hemlock (Tsuga heterophylla), mountain hemlock (T. mertensifolia), and Northern Japanese hemlock (T. diversifolia) are reported to be resistant to infestation. Eastern or Canadian hemlock is very susceptible.
  • Spray smaller trees with a strong stream of water to dislodge adelgids.
  • Prune and destroy heavily infested branches, when practical.
Select non-chemical management options as your first choice!

Chemical Management

Esfenvalerate is toxic to bees. Do not apply products containing esfenvalerate 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.
  • Monterey Bug Buster II
    Active ingredient: esfenvalerate  |  EPA reg no: 1021-1778-54705
  • This list may not include all products registered for this use.

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Caption: Hemlock woolly adelgid
Photo by: R.S. Byther