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Bronze Birch Borer

May 19, 1999

European white birch, gray birch, paper birch, and yellow birch trees that are growing in landscapes are susceptible to bronze birch borer infestations. Adult bronze birch borers are coppery brown with a boat-shaped abdomen. Adult females lay eggs in cracks and crevices or under loose bark on the sunny side of trees. After approximately 2 weeks, eggs hatch into larvae that bore directly into the bark and begin making feeding galleries. Larvae are long and flat with a head that is wider than the body. Larval feeding can result in girdling of the trunk or branches. Infested trees commonly have ridged or swollen bark where larvae have made their zigzag pattern underneath it. Larvae then pupate near the bark surface. After pupation, adults emerge by chewing a D-shaped hole in the bark. Adults feed on the leaves of birch, alder, and poplar.

Prevention is the best way to manage bronze birch borer. These insects prefer stressed trees because they are unable to survive in healthy trees, so proper watering, fertilizing, mulching, and pruning can reduce the potential for bronze birch borer infestations. Birches should not be pruned between May 1 and August 1; this is the general flight period of the bronze birch borer, and females are attracted to pruning cuts. In addition, planting less susceptible varieties of birch such as heritage and whitespire can lead to fewer problems with this insect.

Chemical management of bronze birch borer involves the use of chlorpyrifos (Dursban) or dimethoate (Cygon). These materials should be applied to the bark to kill larvae that hatch from eggs and adults that feed on the bark to provide a site to lay eggs. Cygon should be applied to the bark as a band no more than 6 inches wide.

Author: Raymond A. Cloyd


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