Protecting trees and forests

Hemlock Woolly Adelgid

Find a licensed pesticide applicator to treat your hemlock trees.

Hemlock Woolly Adelgid (HWA), originally from Asia, was first discovered in New Hampshire in Portsmouth in 2000. This small, wingless insect uses its piercing mouth-parts to feed on small hemlock twigs. HWA, left untreated, can kill a tree in 4 to 10 years. Today there are many communities throughout the southeast and lakes region with small infestations. In an effort to slow the spread of this pest, the N.H. Division of Forests and Lands developed an action plan, which includes a quarantine on hemlock material from all infected NH counties.

Untreated outbreaks of HWA weaken the tree and leave it susceptible to damage from other pests, such as elongate hemlock scale and hemlock borer. Maintaining trees in a healthy condition lessens damage by other pests.

The Basics and What to Do

HWA and Other Insects

Important HWA Websites

Towns with Infestations - Alphabetical List
Towns with Infestations
- Map by Year







Harvard Forest's ecologist, David Orwig, discusses threats to our native forests.