Dogwood Borer

The dogwood borer, a native clearwing moth, can be found from southeastern Canada to Florida, and as far west as the Mississippi. The insect has a wide host range including dogwood, pecan, oak, plum, and apple. It is probably the most destructive pest of established flowering dogwood trees. Adults are active during daylight hours.

Description and Life History

The adult dogwood borer is deep blue-black with yellow markings. It has a wing span of about ¾ inch. Both the fore and hind wings are mostly clear. The off-white to cream larvae are 1 inch long with a reddish head capsule. Dogwood borers overwinter as caterpillars in tunnels under the tree’s bark. Larvae change to pupae in spring and, in the Northeast, adult emergence begins in early June and continues into early September, peaking in mid July. Female moths lay eggs on smooth or rough bark. On older trees, they lay eggs in wounds or old borer injuries on the trunk and larger branches. Caterpillars hatch in 8 to 10 days and wander around the bark until an opening is found (the larvae are unable to chew through bark) for their entry into the cambium. Tunneling is confined to the cambium and bark. Once inside, they are well protected and difficult to control. Larvae feed in this protected area throughout most of the year. One generation occurs each year.

Damage

Trees infested with borers show swollen, knotty, calloused, or gall-like areas on the trunk. Dogwood borer adults make irregular burrows under the bark on the trunk, especially at ground level and around the base of limbs or at the edges of wounds or scars on the bark. Fresh sawdust-like borings are usually present on the bark near active borer sites. In young trees, the crown is attacked, resulting in wilting and die-back. Young trees may die completely and older trees may be left with dead or dying branches. Damage by this insect severely limits the success and attractiveness of dogwood.

Control

The general prevalence of dogwood borers and the ease with which they penetrate injured bark makes control difficult. Preventative control measures include: 

• Avoid physical injury to the tree by unnecessary cutting or bruising. Be careful with use of mowers near the base of trees.

• Brace newly transplanted trees to protect against strong winds.

• In some cases, wrapping the trunks of new trees will reduce egg-laying of female moths.

• Plant non-native dogwood varieties less susceptible to dogwood decline, since trees affected by this disease are more likely to be attacked by dogwood borers.

• Maintain optimum growing conditions for trees and remove dead or cankered branches in dry weather.

Dogwood borers are difficult to control once the larvae have gained entry under the bark of a tree or branch. A residual insecticide applied in June may help reduce damage and reduce the number of adults that lay eggs on host trees, but coverage of trees is often expensive and difficult. 

Adapted from: Delaware Cooperative Extension, 1999; NYS IPM Program, Cornell University