Return to Insect Pests

Squash vine borer (Melittia cucurbitae) adults are stout, dark gray moths with ”hairy” red hind legs, opaque front wings, and clear hind wings with dark veins. Unlike most moths, they fly about the plants during the daytime, appearing more like a paper wasp than a moth. The cream-colored, 1-inch larva tunnels into the stems of cucurbits. Symptoms appear in midsummer, when a long runner or an entire plant wilts suddenly. Infested vines usually die beyond the point of attack. Sawdust-like frass near the base of the plant is the best evidence of squash vine borer activity. Careful examination will uncover yellow-brown excrement pushed out through holes in the side of the stem at the point of wilting. The small brown eggs, laid individually on leaf stalks and vines, hatch in seven to 10 days. The newly hatched larva immediately bores into the stem. A larva feeds for 14 to 30 days before exiting the stem to pupate in the soil. A degree-day model has been developed that estimates adult emergence at 1,000 degree-days (base 50°F with a March 1 biofix).

Squash vine borer moth.

(Photo: Ric Bessin, University of Kentucky)

Squash vine borer larva tunneling into cucurbit stem.

(Photo: Ric Bessin, University of Kentucky)

Management:

• The key to management of squash vine borer is controlling the borers before they enter the stem. Once they’re inside the vine, insecticidal control is not possible. Poor timing of sprays is the usual cause of inadequate control.
• Monitor plants weekly from mid-June (or at 900 degree-days) through August for initial signs of borer frass. Very early signs of larval feeding indicate that other eggs will be hatching soon.
• Use two insecticide applications seven days apart to control newly hatching larvae and continue to monitor for additional activity.
• In order to be effective, sprays need to penetrate the canopy to cover the vines.

Return to Insect Pests