Conservation Archive


Jan 1, 2019

David Katz

Hemlock Woolly Adelgid

A variety of invasive species have made the news this year. For people interested in the health of our region’s forests, probably the most worrisome is the Hemlock Woolly Adelgid (HWA). Hemlock Woolly Adelgids, aphid-like insects native to Asia, attach their hypodermic-like mouthparts to hemlock twigs and needles, consume nutrients from the host tree, and reproduce prolifically. Infested trees invariably die, often over a period of 4-10 years, but in as few as 1-2 years in stressed stands. Infestations, characterized by twigs with white, cottony masses, spread rapidly. Older infestations produce greyish crowns and kill literally all hemlocks in their path. HWA has been established south of the Thruway since the late 1980s.

The long-term outlook is hopeful. Cornell University is studying a beetle (Laricobius nigrinus) and two species of silver fly (Leucopis argenticollis and L. piniperda), all native to the Pacific Northwest. These insect parasitoids successfully control the genetically distinct HWA population that affects hemlocks in that region. It is too early to assess the studies, but Cornell hopes that one or more of these predators will also control the HWAs in eastern hemlock forests and allow the forests to recover.

Locally, there’s both good news and bad news. The bad news is that the HWA is moving in our direction faster than expected. It is present in the Oswego area, and this summer was spotted for the first time in the Adirondacks, near Lake George. It is likely that both outbreaks were caused by the trucking of infected nursery stock, which could easily bring the adelgids here, too.

The good news is that scouting allows early detection of outbreaks, and early detection allows effective treatment. The HWAs in Lake George were discovered when only 2 trees were affected, and DEC expects the outbreak to be controlled. Treatment typically involves treating affected trees with insecticides, as the DEC is doing in Lake George.

If you’d like to learn more about the Hemlock Wooly Adelgid (and other invasive species) and get some hands-on scouting experience, Cornell Cooperative Extension and the New York State Hemlock Initiative will host a one-day workshop on January 16, 2019, featuring both classroom and field sessions. Call the Extension office at 315-379-9192 to register, or contact Paul Hetzler at for more information.