Hemlock Decline In the New Jersey Highlands Region

Over the past four decades, the eastern hemlock (Tsuga canadensis) has been
declining in health and vigor in eastern North America. Although other factors
may be involved, the major cause of hemlock decline is infestation by an
introduced, sap-feeding insect, the hemlock woolly adelgid (Adelges tsugae).
Feeding by the adelgid causes hemlock needles to dry up and fall off the tree,
resulting in death to the tree within 2-4 years. Infested hemlock branches
appear to have tiny, cottony masses on the undersides of the twigs where the
needle attaches to the twig. This cottony mass is the egg sac produced by the
adelgid.

Infestation by hemlock woolly adelgid (HWA) is thought to have begun in
Richmond, Virginia around 1953. Dispersed by wind, birds, mammals, and even
humans, HWA has spread into hemlock forest stands in eleven states from
Massachussettes to North Carolina. The hemlock woolly adelgid infestations
appeared in New Jersey during the mid-1980's and caused significant mortality
to some of the more noted stands in the state by the early 1990's.