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Wood-Boring Insects

May 9, 2001

Be on the lookout for wood-boring insects (beetles and moths), a problem in nurseries and landscapes. Insects active at this time of year include bronze birch borer (Agrilus anxius), flat-headed appletree borer (Chrysobothris femorata), round-headed appletree borer (Saperda candida), peachtree borer (Synanthedon exitiosa), and viburnum crown borer (Synanthedon fatifera). In general, females lay eggs on exposed bark; eggs hatch into larvae that tunnel through the cambium. Larvae feed within the sapwood or heartwood; adults feed on leaves or flower nectar.

The key to managing wood-boring insects is to keep plants healthy and avoid stress by maintaining proper cultural practices–watering, fertility, mulching, and pruning. Also, avoid mower or weed-whacker injury to the base because this removes essential cam-bium tissue that transports food upward to leaves. This injury places undue stress on plants. Many wood-boring insects are opportunistic and thrive on stressed plants; healthy plants are less susceptible. Pruning trees or shrubs at certain times of year can in-crease problems with wood-boring insects. For exam-ple, generally avoid pruning birch trees, especially white birch, May to August because bronze birch borer adults are flying around looking for places to lay eggs. Pruning during this time creates wounds that emit odors, attracting the females. Newly planted trees or shrubs are highly susceptible to borer attack. For example, the flat-headed appletree borer attacks recently planted plants because they are stressed, in-creasing their susceptibility; it is important to properly water and mulch young plants to minimize stress.

Pest-control materials may be used to avoid prob-lems with wood-boring insects. Phasing out of chlor-pyrifos (Dursban), due to the Food Quality Protection Act (FQPA), is causing concern about availability of effective pest-control materials for managing wood-boring insects; chlorpyrifos will not be available to homeowners at the end of 2001. However, it will still be available for commercial operators for several years. Presently, the alternative pest-control materials that have demonstrated efficacy against various wood-boring insects include dimethoate (Cygon), lindane, and permethrin (Astro). Residual activity often de-pends on bark characteristics, with activity generally lower on smooth bark (as in birch) compared to ridged or furrowed bark. The insecticide binds more easily to rough bark; also, there is less potential for wash-off from rain or irrigation. It is important to thoroughly soak the bark up to 5 feet from the tree base because adult borers tend to lay eggs there.

The timing of bark applications is critical. Make them before eggs hatch or when adults emerge be-cause most insecticides do not penetrate bark after insect entry. Once larvae are inside the tree, very little can be done except maintain plant health. Recent studies show that imidacloprid (Merit, Imicide, and Pointer) may have some activity on wood-boring insects; however, more data is needed. Als

Author: Raymond A. Cloyd


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