Issue 10, June 27, 2011

Flatheaded Appletree Borer

Flatheaded appletree borer attacks a variety of rose family trees including crabapple, hawthorn, serviceberry, mountain ash, and ornamental pears, plums, and cherries. It also attacks maple, ash, and a variety of other trees. Now is the time to treat for this pest.

Flatheaded appletree borer generally attacks trees or parts of trees under stress. It commonly attacks older rose family trees, assisting in their death. Particularly in the northern two-thirds of Illinois, serviceberry, mountain ash, flowering cherry, purple-leaf plum, and Bradford and Callery pears are short-lived trees, frequently dying within 30 years. As these trees decline, flatheaded appletree borer frequently attacks them. With homeowners and other clientele commonly assuming that all trees live for a hundred years or more, this natural decline and borer attack is difficult for them to understand.

It also frequently attacks maples that have been recently transplanted as well as those with frost crack injury or storm breakage. Maples in nurseries and new landscapes are typically attacked near the base of the tree. The larva tunnels under the bark in a helical fashion around the trunk, girdling and killing the tree. Larvae are likely to tunnel beyond the frost crack or storm damaged area, causing additional damage. Frothy sap commonly exudes through bark cracks in damaged areas.

Larvae tunnel through the cambium with older larvae tunneling into the heartwood. The tunnels are broad and packed with frass. Fully grown larvae are about one inch long. Pupation occurs in the heartwood with adult beetles emerging at this time of year through oval holes that are about three-sixteenths inch in diameter. Adult beetles are about one-half to three-fourths inch long, long-oval in shape, and grayish-bronze. The wing covers are rough with small bumps. After mating, females lay eggs for the next generation in wounds and in cracks in the bark.

Newly transplanted trees should be watered when necessary to keep them as healthy as possible. Other cultural practices assisting in adaptation to site and rapid growth help reduce borer attack. Plastic or paper trunk wraps reduce borer attack, but be watchful for disease development under that wraps.

Application at this time of imidacloprid (Merit, Xytect, others) is effective to newly transplanted stock and damaged trees. Spraying the bark should provide control. Application to trees declining due to age may extend longevity only a couple of years and is usually not recommended. (Phil Nixon)

Phil Nixon

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