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Hemlock Woolly Adelgid

Hemlock Wooly Adelgid
Hemlock Woolly Adelgid. Photograph credit:
Chris Evans, The University of Georgia

The hemlock woolly adelgid (Adelges tsugae) (HWA) is native to parts of Asia and was first discovered in New York in 1985. It is in the family Adelgidae, which is related to aphids. The adelgid uses long mouth parts to extract sap and nutrients from hemlock foliage, this prevents free 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. Infestation is usually fatal to the host after several years. Valued plantings of the shade-loving eastern hemlock (Tsuga canadensis) can be ravaged by the hemlock woolly adelgid, and the natural stands of hemlock in the forests and parks in upstate New York would be greatly affected if the pest spreads to those locations. The wind, birds, other wildlife and the movement of infested host material (wood) by humans are all factors in the dispersion of the adelgid.

Distribution in New York

From the first discovery of the hemlock woolly adelgid in the Hudson Valley in the 1980's, the insect has spread north and west to the Catskills, the Capital Region and even the Finger Lakes and other parts of Western New York. In the summer of 2017, HWA was discovered in the Town of Lake George, the first known occurrence in the Adirondack Park. A press release of the incident can be found on DEC's website. Currently 43 New York counties are infested with the hemlock woolly adelgid.


The most effective way to manage HWA and protect hemlock trees is through the application of insecticides to the basal bark area of the tree, typically done in the spring or fall. This work is done in high priority hemlock stands around the state, using two specific chemicals, imidacloprid and dinotefuran. For more information about chemical control of HWA, please see NYSDEC's Frequently Asked Questions document (PDF, 640 KB).


To learn more about hemlock woolly adelgid, please see the Links Leaving DEC's Website in the right column. To report a sighting of this insect, go to "Look for and Report Hemlock Woolly Adelgid" below or in the column to the left.

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