Hemlock Woolly Adelgid (HWA) is an invasive pest that has threatened hemlocks throughout eastern United States since the early 20th century. An estimated 50 percent of the eastern hemlock range has been affected.
This small, aphid-like pest varies in color from brown to red, is oval-shaped and only about 1/32 inch long.
Nymphs are approximately 1/8 inch in diameter and produce a white, cottony substance that covers their bodies. The presence of these white masses on a hemlock tree is a sure way to identify a Hemlock Woolly Adelgid infestation.
Feeding causes needles on infested branches to dry up, turn grayish-green and drop from the tree, preventing new buds. Dieback of major limbs can occur within two years and progresses from the bottom of the tree upward. Heavy infestations can kill trees in as little as four years.
Hemlock Woolly Adelgids are found in Georgia, Tennessee, Virginia, South Carolina, North Carolina, Kentucky, West Virginia, Pennsylvania, New York, Maine, New Hampshire, Vermont, Massachusetts, Michigan, Rhode Island, Connecticut, New Jersey, Delaware, Maryland and the District of Columbia. They feed exclusively on Canada and Carolina hemlock trees.