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Flatheaded Appletree Borer

May 10, 2000

Flatheaded appletree borer, Chrysobothris femorata, attacks a wide range of trees and shrubs, especially those in the rose family (Rosaceae), such as cotoneaster, crabapple, hawthorn, pyracantha, and rose. In addition, young maple trees are highly susceptible to borer infestations. Adult beetles attack plants growing in nurseries and landscapes. The adults are 10 to 12 millimeters long with a somewhat flattened appearance. They are metallic and vary in color from brown to gray. Adult females lay eggs in bark crevices. The eggs hatch into legless, creamy-white larvae that bore through the bark into the cambium. The larvae are about 1 inch 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 sus-ceptible to injury. Eventually, the larvae bore into the heartwood to pupate. The adults that emerge leave a D-shaped hole. There is only one generation per year.

Proper irrigation and fertility will promote healthy, vigorous growth and minimize attacks by the flat-headed appletree 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 post-emergent herbicide (i.e., Roundup, Finale, Reward, or Scythe) may reduce potential problems with flat-headed appletree borer. Applications of the insecticide chlorpyrifos (Dursban) or lindane in late May or early June will kill eggs and the newly hatched larvae before they bore into trees.

Author: Raymond Cloyd


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