|The Botanic Garden
of Smith College
he hemlock woolly adelgid (Adelges tsugae) is an aphidlike insect introduced from Asia that is decimating natural and landscape trees of Canada hemlock (Tsuga canadensis) and other North American hemlock species. Asian hemlocks have a certain tolerance to the pest, which inserts its mouthparts into plant vessels and withdraws plant sap, eventually killing the tree. The insect has a mobile stage followed by an immobile stage, and it may develop a second, opportunistic phase that attacks Asian spruces.
Hemlock woolly adelgid is very difficult to control in forests and hedges, but single specimens can be treated with horticultural oils (complete coverage must be achieved) and/or systemic insecticides. The adelgid was first noted on the Smith campus in 1996 (for more information, see the article by Bill Belden in the Fall 1998 issue of Botanic Garden News).
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