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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

Best Management Practices

Research Issue

[image:] Cover from publication - .  Eastern Hemlock Forests: Guidelines to Minimize the Impacts of Hemlock Woolly Adelgid.Eastern hemlock (Tsuga canadensis) is the most shade-tolerant and long-lived tree species in eastern North America. Its unsurpassed ability to tolerate low light enables it to form dense canopies and stands that provide a unique habitat for many plant and wildlife species. Carolina hemlock (Tsuga caroliniana) is a relic species limited to a small area in the southern range of eastern hemlock. Both species are being threatened by the accidentally introduced hemlock woolly adelgid (HWA) (Adelges tsugae). Control of the HWA is a challenge. An unusual life cycle, presence of susceptible hosts, and a lack of natural enemies contribute to explosive population increases and rapid spread of the adelgid. Until effective controls are discovered, it is anticipated that the adelgid will continue to spread in eastern forests and mortality of hemlock will increase. Decline of eastern hemlock will lead to a loss of habitat diversity and a decrease in the esthetic beauty in many of our forests as hemlock is replaced by hardwood species such as black birch (Betula lenta) and red maple (Acer rubrum).

Because hemlocks can survive for several years after initial infestation by HWA, forest managers have time to take steps to minimize its impact. Therefore, a group of foresters and entomologists organized existing information into a handbook with guidelines to help resource managers make informed decisions in preparing management plans for hemlock stands that are, or will be, infested with HWA.

Research Results

The handbook summarizes current scientific knowledge of the impact of HWA on eastern hemlock forests and the processes involved in rehabilitating hemlock stands that have been, or will be, damaged by HWA. Part 1 presents the biology and ecology of eastern hemlock and HWA. Part 2 provides guidelines to help managers make decisions about the salvage and rehabilitation of damaged hemlock stands in order to recover, to the extent possible, the ecological and esthetic attributes associated with hemlock forests. These guidelines are summarized as:

  • Develop a management plan before adelgid infestations and hemlock damage occur
  • Identify those stands that are at risk and prioritize them for treatment according to ecological, esthetic, and economic values
  • Monitor the prevalence of HWA and hemlock health
  • Preserve valuable hemlocks with appropriate cultural and chemical controls and encourage the establishment of biological controls where possible
  • Protect public safety by removing dead and dying hemlocks near roads and trails
  • Conduct harvest operations using Best Management Practices to protect forest soils and water quality in adjacent wetlands and riparian areas
  • Establish evergreen cover, where possible, with mixed species plantings to restore some of the ecological and esthetic characteristics that had been provided by hemlock

Ward, Jeffrey; Montgomery, Micheal; Cheah, Carole ; Onken, Brad; Cowles, Richard  2004.  Eastern hemlock forests: Guidelines to minimize the impacts of hemlock woolly adelgid.  Morgantown, WV: U. S. Department of Agriculture, Forest Service, Northeastern Area State & Private Forestry.

Research Participants

Principal Investigators

  • Jeffrey Ward, Station Forester, The Connecticut Agricultural Experiment Station, New Haven, CT
  • Mike Montgomery, Research Entomologist, U.S. Forest Service, Northern Research Station

More Information

  • Nathan Havill, Research Entomologist, U.S. Forest Service, Northern Research Station
  • Melody Keena, Research Entomologist, U.S. Forest Service, Northern Research Station

Last Modified: 05/07/2015