Hemlock (Tsuga)-Hemlock woolly adelgid

Adelges tsugae

Pest description and damage Hemlock woolly adelgids are aphid-like insects. They appear as white, woolly tufts on the bark, branches and needles of twigs. Adults are black beneath the woolly waxy material. While needles may drop prematurely, weakening the tree and sometimes leading to death of branches, more often in landscapes infestations are limited to single branches without dire consequences. A few adelgids usually do not require action. Trees with severe infestations are stressed, predisposing them to other insect and disease problems. The hemlock adelgid is especially a problem on hemlock hedges.

Biology and life history The adelgid overwinters as woolly adults. Reddish-brown crawlers, similar to scale crawlers, appear in spring and early summer. Hemlock adelgids are known as "hemlock chermes."

Pest monitoring Inspect woolly areas for the presence of live adults or tiny black dots on the needles which indicate the scale crawlers are alive and active. Also, check for evidence of natural enemies.

Management-cultural control

Western hemlock (Tsuga heterophylla), mountain hemlock (T. mertensifolia), and Northern Japanese hemlock (T. diversifolia) are reported to be resistant to infestation. Eastern or Canadian hemlock is very susceptible. Wipe off minor infestations and prune out larger infestations if possible.

Management-biological control

Often the woolly material will appear dirty and disturbed. Look for syrphid larvae, white waxy ladybug larvae, lacewing larvae and other predators.

Management-chemical control

See Table 1 in: