Publication 444-217, August 1996
Lepidoptera: Sesiidae, Synanthedon scitula
PLANTS ATTACKED: Dogwood, pecan, elm, hickory, and willow
DESCRIPTION OF DAMAGE: Larvae feed in the inner bark of live, healthy dogwood trees. The damaged area of the trunk or branch swells and eventually the bark will fall off. Leaves turning red prematurely in mid-summer on a lone branch are an early sign of dogwood borers. Infested branches and limbs will die. Dogwood borers often will not kill the tree in the first year, but reinfestation in successive years will.
IDENTIFICATION: Dogwood borer larvae are white with pale brown heads and they bore in the cambium of dogwood, gaining entrance under rough bark or through wounds. Late-summer adults are clear wing moths and somewhat resemble wasps. The body is blue with yellow stripes and yellow-banded legs.
LIFE HISTORY: Dogwood borers overwinter as larvae under the bark. The larvae usually pupate in the spring and emerge in late May and June, but may pupate and continue to emerge throughout the summer. Adults are active from May until September. Adults mate and eggs are laid on wounds or old borer injuries. After hatching, the small, light-colored larvae wander over the branches until an entrance point is reached. Tunneling is confined to the cambium and bark. The larvae, in all stages, overwinter. There is only one generation per year.
CONTROL: Insecticides applied to the trunk and damaged areas beginning in mid-May provide effective control. The treatment should be repeated at 6-week intervals 2-3 times. A fine wire inserted into the entry hole will sometimes kill the larvae.
In addition, some cultural practices will reduce borer injury. Regularly watered and fertilized trees are able to maintain vigor and are less susceptible to borer injury. Avoid pruning during the summer months when the moths are laying eggs and avoid wounding or injuring the tree. See the Virginia Pest Management Guides for Home Ornamental Plants or for Nursery Ornamentals for specific control recommendations. If pest management guides are not available, see your Extension agent for specific recommendations in your area.
REMARKS: Special care should be taken to treat all wounds or injuries to dogwoods, etc., to prevent infestations with borers attracted by the resinous smell released from the wounds.
Prepared by Eric Day, Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 2406l-03l9.
