The hemlock woolly adelgid (related to aphids) is a serious pest of Canadian hemlock in the eastern United States and of western hemlock used as an ornamental in the Pacific Northwest. The adelgid injures hemlocks by sucking sap from needles and twigs.
Look for white, cottony masses attached to the bottom of hemlock needles and twigs. Heavy infestations resemble a coating of snow. Initially, hemlock needles discolor and drop prematurely.
As the infestation progresses, the tree looses vigor, twigs and branches die and eventually the tree could die.
Treatment and Management
Horticultural oil applications in April, July and October may be necessary to effectively control a large infestation.
Fertilization with Arbor Green PRO® will help increase your hemlock's tolerance of environmental stress. Additionally, an insecticide application will help the tree rebound from feeding damage.