Issue 4, May 14, 2010
Flatheaded Appletree Borer
Flatheaded appletree borer attacks trees in the rose family, being common in older hawthorn, serviceberry, cotoneaster, rose, and crabapple branches and trunks where it primarily attacks declining trees and shrubs near the end of their lifespan. It also attacks dead and dying branches of many other tree species, including maple, oak, ash, hickory, sycamore, tuliptree, and willow. In these situations, it is normally not considered to be a pest.
Flatheaded appletree borer is a serious pest of young maples, attacking nursery and recently planted stock. It typically attacks young maples just above the soil line, tunneling upward in the cambium just under the bark in a helical fashion around the trunk. Attacked trees are commonly killed or have severe dieback.
There is one generation per year. Adult beetles are about one-half inch long and oval, being metallic brown to black. They lay eggs singly in bark crevices. These eggs hatch into larvae that tunnel into the trunk. The legless larvae are whitish with dark mouthparts and grow to slightly more than one inch long.
Flatheaded appletree borer is susceptible to control at this time throughout the state. Spraying the lower few feet of the trunk with imidacloprid (Merit) should be effective to prevent girdling and other weakening of the trunk near the soil surface.
Encouraging growth and heavy sap flow with proper fertilization and other cultural practices helps reduce successful attack by flatheaded appletree borer. Hatching larvae are drowned in heavy sap flow. There is some evidence that wrapped trees are less susceptible to attack, but wrapping left on during the growing season may increase susceptibility to fungal diseases. It also appears that this insect is more of a problem where tall grass is allowed to grow around the young trees. Mowing or other vegetation control is recommended.--Phil Nixon