Native to Asia, the hemlock woolly adelgid, or HWA, is an invasive, aphid-like insect that attacks North American hemlocks. HWA are very small (1.5 mm) and often hard to see, but they can be easily identified by the white woolly masses they form on the underside of branches at the base of the needles.
Juvenile HWA, known as crawlers, search for suitable sites on the host tree, usually at the base of the needles. They insert their long mouthparts and begin feeding on the tree's stored starches. HWA remain in the same spot for the rest of their lives, continually feeding and developing into adults. Their feeding severely damages the canopy of the host tree by disrupting the flow of nutrients to its twigs and needles. Tree health declines, and mortality usually occurs within 4 to 10 years.
All species of hemlock are vulnerable to attack, but severe damage and death typically occurs in eastern (Tsuga canadensis) and Carolina (Tsuga caroliniana) hemlocks only.
- White woolly masses (ovisacs) about one-quarter the size of a cotton swab on the underside of branches at the base of needles
- Needle loss and branch dieback
- Gray-tinted needles
Infested hemlock trees can be treated using an insecticide to prevent infestation. This can be accomplished using Mauget Injection Capsules to inject specialized insecticides into holes drilled at several locations around the circumference of the tree. Mauget Imicide and Mauget Dinocide are the most effective.