Hemlock trees are an important part of forest systems, providing protection from erosion as well as food and shelter for wildlife. Hemlocks are a vital resource for the timber industry, but are also highly regarded for the ornamental beauty they add to landscapes. But these trees are under attack. The culprit? Hemlock Woolly Adelgid (HWA), a pest that’s threatened hemlocks throughout eastern portions of the United States since the early 20th century. In 2007, Virginia Tech College of Agriculture and Life Sciences reported an estimated 50 percent of the eastern hemlock range had been affected. A 2009 study by the U.S. Forest Service Southern Research Station found that the Hemlock Woolly Adelgid was killing hemlocks in the southeast at an even faster rate than in the northeast.
What It Looks Like
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.
The Threat It Poses
Feeding causes needles on infested branches to dry up, turn grayish-green and drop from the tree, preventing new apical 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.
The following states and districts have established HWA populations: Georgia, Tennessee, Virginia, South Carolina, North Carolina, Kentucky, West Virginia, Pennsylvania, New York, Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New Jersey, Delaware, Maryland and the District of Columbia.
How You Can Help
Contact your local USDA Animal and Plant Health Inspection Service (APHIS) office [http://www.aphis.usda.gov/] if you think you’ve found an HWA infestation.
Treating Your Trees
Protect your trees against Hemlock Woolly Adelgid with a foliar spray or a systemic insecticide applied as a soil drench at the base of the tree.
Products that kill or prevent this pest (liquid formulations only)