Lesser Peachtree Borer
Lesser peachtree borer, Synanthedon pictipes, is an important pest in peach and cherry orchards throughout Pennsylvania and surrounding states. Problems are almost always associated with widespread incidence of Cytospora canker and, to a much lesser extent, pruning wounds, winter injury, and mechanical damage.
Adults are day-flying moths that resemble wasps. Veins and margins of transparent wings are fringed with steel-blue scales; the body is blue and narrowly fringed with yellow. Males of lesser peachtree borer have yellow scales on the top of the head between the eyes and black scales between the antennae. This combination differentiates them from peachtree borer males, which have black scales between the eyes and yellow scales between the antennae. Lesser peachtree borer larvae are white with a yellowish-brown head and reach 1 inch at maturity.
There are two generations each year; the first flight occurs during May and June, and the second during August and September. The lesser peachtree borer overwinters as larvae and reaches full growth during April and May. Larvae eat an exit hole nearly through the bark, spin a cocoon, and pupate in a small cavity. In 3 to 4 weeks, a clear-winged moth emerges, leaving an empty pupal skin projecting from the burrow. Adults are active for several weeks. The female moth is capable of laying several hundred eggs in cracks, under bark scales, and in cankered areas. Moths are attracted to trees that have been injured or previously infested. Eggs hatch in a week to 10 days, and young worms move to the inner bark and continue to feed.
Growers first notice evidence of borer infestation by checking for pupal skins in cankered areas. An early sign of lesser peachtree borer injury is the presence of wood chips, sawdust, and frass produced by feeding borers in the gum in cankered areas. If the gum does not contain this particulate material, the injury is probably not caused by borers. As an aid in timing sprays, growers should obtain pheromone trap records on flight activity. Treat at peak flight, usually toward the end of June, if there is an average of more than two borers per tree, and again in late summer. If fewer than two pupal skins are located in each tree, target only the second generation in late summer.
Any horticultural practice that prevents canker and maintains good tree development will help prevent borer damage. If chemical control is necessary, high-volume handgun sprays thoroughly wetting trunk and scaffold limbs are recommended, with at least 1 gallon of spray mixture applied per tree. The late-summer spray can be applied after harvest. If peachtree borer is also a problem this spray should be made within the first 2 weeks of September. If only lesser peachtree borer is present, sprays may be applied to late-maturing varieties in early August. Do not allow spray residue to contaminate fruit.