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Pest Alert United States Department of Agriculture
Forest Service
Northeastern Area


Hemlock Woolly Adelgid

The hemlock woolly adelgid, Adelges tsugae, has been in the United States since 1924. This introduced insect, believed to be a native of Asia, is a serious pest of eastern hemlock and Carolina hemlock. In the eastern United States it is present from the Smoky Mountains, north to the mid Hudson River Valley and southern New England.

White cottony sacs at the base of the needles are good evidence of a hemlock woolly adelgid infestation. These sacs resemble the tips of cotton swabs. They are present throughout the year, but are most prominent in early spring.

The hemlock woolly adelgid feeds during all seasons with the greatest damage occurring in the spring. It is dispersed by wind, birds and mammals.

By sucking sap from the young twigs, the insect retards or prevents tree growth causing needles to discolor from deep green to grayish green, and to drop prematurely. The loss of new shoots and needles seriously impairs tree health. Defoliation and tree death can occur within several years.


Photo 1. Egg masses produced by overwinterning adults.
Photo 1. Egg masses produced by overwinterning adults. (Click for detail. JPG 29K).


Photo 2. Discolored foliage and twig dieback caused by feeding nymphs.
Photo 2. Discolored foliage and twig dieback caused by feeding nymphs. (Click for detail. JPG 30K).


Photo 3. Hemlock stand heavily damaged by hemlock woolly adelgid.
Photo 3. Hemlock stand heavily damaged by hemlock woolly adelgid. (Click for detail. JPG 38K).


For additional information contact your State Forester, State Entomologist, State Extension Specialist, or County Agricultural Agent.

Technical Advisor, photo credits: Mark McClure, Connecticut Agricultural Experiment Station

 

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