Squash Vine Borers

Fall is harvest season for squash, but there’s someone else who wants to get to those plants before you do—the squash vine borer. Here’s how to prevent these pests from ruining your squash harvest.

Fall is harvest season for squash, but there’s someone else who wants to get to those plants before you do—the squash vine borer. Here’s how to prevent these pests from ruining your squash harvest.

Vine borers are the larvae of a orange and black clearwing moth. They look like white caterpillars, but you generally won’t see them since they do their dirty work on the inside of your plants.

Adult moths lay their eggs at the base of squash (and pumpkin, melon or cucumber) plants in mid-summer, and the young bore through the stems, eating the plants from the inside and turning an otherwise healthy-looking plant into a pile of brown mush. After they’re done feeding, they drop into the soil to pupate and emerge as moths, laying eggs on plants and starting the cycle of destruction all over again.

One calling card of their damage are tiny holes in plant vines and nearby droppings that lok like sawdust. If you notice these signs on wilting squash plants apply Bt or insecticidal soap to the vines to kill them as they dine. You can also cut the vines lengthwise to find and destroy the white caterpillars inside, or pull out affected plants and destroy them.

By the time you see the mushy damage, the plants are most likely past the point of rescue. But you can prevent squash vine borer larvae from maturing and laying eggs on next season’s crop. The following season, set out traps for the adults. Use a yellow bowl or pan filled with water. Look for individual brown eggs at the bases of new plants and wipe them off.