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Flat-Headed Apple Tree Borer

May 26, 1999

Flat-headed apple tree borer attacks a wide range of trees and shrubs, including plants in the rose family (Rosaceae) such as crabapple, rose, hawthorn, cotoneaster, and pyracantha. Young maple trees are also highly susceptible to borer infestations. Adult beetles attack plants growing in nurseries and landscapes. The adults are 12 mm long, with a somewhat flattened appearance. They are metallic and vary in color from brown to gray. Adult females lay eggs in bark crevices, and the eggs hatch into legless, creamy white larvae that bore through the bark into the cambium. The larvae are 25 mm long when full grown. They produce long, winding, tortuous tunnels in the cambium that can girdle and kill large branches and young trees. Larval activity can usually be detected by the presence of white sap flowing from cracks in the bark. Newly transplanted trees and shrubs are highly susceptible to injury. Eventually, the larvae bore into the heartwood to pupate. Adults that emerge leave a D-shaped hole. There is only one generation per year.

Proper fertilization and irrigation promote healthy, vigorous growth and minimize attacks by the flat-headed apple tree borer. A horticultural wrap of paper or burlap may be useful in protecting young trees and shrubs. In nurseries, clean cultivation, removing grassy weeds by mowing, or using a postemergent herbicide may reduce potential problems with flat-headed apple tree borer. Chemical management consists of spraying plants in late May or early June with chlorpyrifos (Dursban) or lindane. Spray applications made at this time kill eggs and the newly hatched larvae before they bore into trees.

Author: Raymond A. Cloyd


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