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vermont invasive forest pest update

Hemlock Woolly Adelgid

Adelges tsugae


Brief Introduction

The hemlock woolly adelgid is a tiny insect from east Asia that attacks forest and ornamental hemlock trees. It feeds on young twigs, causing needles to dry out and drop prematurely. Trees may die in four to six years. Some survive, but with sparse foliage, losing their value as shelter for wildlife and their ability to shade streams. Hemlock is our 7th most common tree, so this insect will have a major impact as it spreads in Vermont. hemlock woolly adelgid egg masses
Plant hardiness zone map of Vermont with HWA detections

Where is the pest?

Hemlock woolly adelgid was observed in Virginia in the early 1950’s and has now spread from Georgia to Maine. In 2007, it was found on native trees in Vermont for the first time. It is now known to occur in Windham and Bennington Counties.  It has also been detected in Windsor County.


What’s being done about it?

Tactics used to combat hemlock woolly adelgid infestations include release of natural enemies like predatory beetles and pathogenic fungi, preserving genetic resistance, regulations to prevent the movement of infested hemlocks, and pesticide treatments.
  What are we doing in Vermont?
  The Department of Forests, Parks & Recreation is collaborating with the Agency of Agriculture, Food, and Markets and the states of New Hampshire and Maine to manage the insect and to find out more about how it affects trees as it moves north. The U.S. Forest Service helps support these projects.
  • Surveys
    • Citizen volunteers have been trained and are assisting with detection surveys in Bennington, Windsor and Windham Counties.
  • Quarantines
    • A quarantine regulates the movement of hemlock from infested counties.
  • Control
    • We are participating in forest impact and management research projects in cooperation with the U.S. Forest Service and local universities.
    • A cold-hardy predatory beetle from the northwestern U.S. has been released in infested stands in Windham and Bennington Counties.  We have also used pathogenic fungi and chemical treatments to slow the spread of the insect.


  • Familiarize yourself with hemlock woolly adelgid and look for potential infestations. The most obvious sign is a white, woolly mass found on the underside of twigs at the base of needles. If you’re interested in doing more, volunteer to participate in the citizen monitoring program.
  • Remove bird feeders and baths from early April until August, to reduce spread by birds.
  • When purchasing hemlocks, check that they don’t come from areas with hemlock woolly adelgid.
  • If shipping hemlock products, stay abreast of changing quarantine regulations.
  • Don’t rush to salvage hemlock. Our cold winter temperatures can be lethal to hemlock woolly adelgid.

For More Information

Vermont Hemlock Woolly Adelgid Information:

General information:,

Distribution map:

Quarantine information:

Recommendations for landowners: for landowner response.pdf

This insect will have a major impact as it spreads into Vermont. The sooner we find new infestations, the better our chances of slowing its spread to other trees nearby or to other areas, and of eradicating it where it has been detected.

If you suspect this pest occurs in your area or for more information, contact the Forest Biology Lab at 802-879-5687, or Windsor & Windham Counties Springfield (802) 885-8845
Bennington & Rutland Counties Rutland (802) 786-0060
Addison, Chittenden & Grand Isle Counties Essex Junction (802) 879-6565
Lamoille, Orange & Washington Counties Barre (802) 476-0170
Caledonia, Orleans & Essex Counties St. Johnsbury (802) 751-0110
VT Department of Forests, Parks & Recreation, May 2014.









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