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Northern Research Station
One Gifford Pinchot Drive
Madison, WI 53726
(608) 231-9318
(608) 231-9544 TTY/TDD

Hemlock Woolly Adelgid

Control and Management

Research into the best ways to control and manage hemlock woolly adelgid (HWA) includes discovery and evaluation of potential biological control agents, evaluation and improvement of methods for chemical control, evaluation of silvicultural options, and development of host plant resistance (both through hybridization and identification of putatively resistant trees in the infested area).

Control with traditional insecticides is limited to individual tree treatments in readily accessible, non-environmentally sensitive areas.  There are no practical means to manage HWA in forest environments.  Eradication efforts have centered on tree removals and multiple chemical insecticide treatments to individual trees.  In short, the tools available to manage this pest have been limited and inadequate.  Research is directed at developing and implementing insecticide treatment strategies to limit the impact of HWA in the forest environment.  Research also is being conducted to improve the methods for protecting individual, high value trees in urban and recreation areas.

Biological control efforts have focused on HWA predators and pathogens, because there are no known parasites of adelgids.  Activities to date have included (1) exploration in western North America, China, and Japan to identify, evaluate, and collect HWA natural enemies, (2) lab and field assessments to determine host specificity and suitability to climate and site conditions in eastern North America, (3) mass-rearing of promising natural enemies, and (4) establishment and evaluation of selected natural enemies throughout the infested region. To date, three beetle predators (Sasajiscymnus tsugae, Laricobius nigrinus, and Scymnus sinuanodulus)have been released widely.  Small numbers of a fourth beetle predator (S. ningshanensis) was released for the first time in 2007 in Massachusetts and Connecticut.  Additional predators from China, Japan, and western North America are being evaluated. Insect-rearing facilities currently involved in mass-rearing these predators include the New Jersey Department of Agriculture, North Carolina Department of Agriculture, Virginia Tech, University of Tennessee, University of Georgia, and Clemson University.  Mass-rearing HWA predators requires large quantities of field-collected host; efforts to develop artificial diets are currently underway.

Host resistance research requires a long-term commitment, but this can be shortened if the mechanisms responsible for resistance can be identified.  Once hemlocks with resistant genotypes are identified, they must be evaluated for desirable growth characteristics and propagated.  Until biological control and/or host resistance can prevent HWA from annihilating eastern hemlocks, actions are needed to preserve the extent of genetic variation in native T. canadensis and T. caroliniana.

Research Areas

Last Modified: 05/08/2015