IDENTIFICATION — There’s nothing worse than having your squash die on the vine because of squash vine borers. Adult moths are about 5?8 in. long with translucent wings. They have an orange and black striped body with fringed hind legs. Females emerge in spring to lay pinhead-sized eggs on the lower 3 to 4 ft. of squash vines.
Once the eggs hatch, the larvae bore into the stem and start eating. They grow up to an inch long with a white body and brown head. Larvae live and eat in the vine for four to six weeks, then move from the plant into the soil, where they spend the winter in a cocoon.
DAMAGE — Squash, zucchini, pumpkins and gourds are all susceptible to attack by these pests. Their favorite variety is Hubbard squash. Butternut squash, cucumbers and melons are less palatable but are sometimes affected. If the vines in your garden suddenly wilt, take a look at the base of the plant. Look for small holes in the vine, along with an accumulation of sawdustlike material. That’s frass, the debris larvae produce as they eat their way through the vine. As they eat, the larvae cut off water and nutrients, which kills the plant.
CONTROL — Because squash vine borer larvae are inside the vine, it’s difficult to get rid of them. But if you keep at it, you can minimize damage. In late spring, spray the vines weekly with an insecticidal soap to smother the eggs. Or spray the vine with Bt before the eggs hatch. This natural insecticide is safe to use on vegetables but needs to be eaten by the pest to be effective. In fall, destroy the vines as soon as possible after harvest to get rid of any remaining larvae. If you can till the soil to expose any cocoons to cold and predators, that will help, too.