Insects, Pests, Diseases & Weeds
The hemlock woolly adelgid (HWA), a destructive aphid-like insect pest of eastern and Carolina hemlock, is originally from Asia. Its first discovery in the United States was in Oregon on western hemlock in the 1920s. It was not found in the East until the 1950s, when it was detected in Virginia. Since then it has spread throughout the East from New England to North Carolina (1995) and most recently to East Tennessee in 2002. The HWA is expanding its range an average of 15 miles per year.
The hemlocks found in Asia and the western and mountain hemlocks that occur in the western United States appear resistant to HWA. Conversely, the eastern and Carolina hemlock found in the East are highly susceptible. Nearly half the hemlock stands in the eastern forests are infested with this pest, which has caused extensive tree mortality, up to 80 percent, in the Middle Atlantic and southern New England states.
"SP503-G The Hemlock Woolly Adelgid - A Threat to Hemlock in Tennessee," The University of Tennessee Agricultural Extension Service, 04-0005 SP503G-5M-3/04 E12-4615-00-002-04, http://trace.tennessee.edu/utk_agexfores/28