Hemlock: Hemlock woolly adelgid
Photo by: R.S. Byther
Biology
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 problms. 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
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!
- 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.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- 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.
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.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.