Goal: Deliver Benefits to the Public Managing hemlock woolly adelgids

A nonnative invasive insect, the hemlock woolly adelgid (HWA), threatens the ability of natural resource managers to maintain eastern and Carolina hemlocks as critical components of unique forest ecosystems in eastern North America. Although substantial progress has been made in both chemical and biological control of HWA, neither of these tactics applied alone is expected to provide adequate control of HWA throughout its introduced range.

A new USDA Forest Service resource manager’s guide titled “Integrating Chemical and Biological Control of the Hemlock Woolly Adelgid” presents a strategy for using biological and chemical control together in the same forest stands. The goal of the strategy is to prolong hemlock health on certain hemlock trees through temporary insecticide protection, while simultaneously establishing predators on nearby untreated trees.

Temporarily-protected hemlocks are expected to eventually support predators after their chemical treatment wears off. A separate research project showed that Laricobius nigrinus, a predatory beetle, significantly reduced populations of the winter generation of the hemlock woolly adelgid. However, this beetle inactive in the spring, suggesting the need for additional predators and control measures.

Another research project confirms that silvicultural treatments that allow more sunlight to shine on eastern hemlock trees can make them healthier, even if they are infested with hemlock woolly adelgids. Researchers are working to develop management recommendations, and plan to update the manager’s guide.

Webinar on the manager’s guide presented through Emerald Ash Borer University

Related article: To save the hemlock, scientists turn to genetics and natural predators - The Washington Post