Squash Vine Borer
On Crops: Summer and winter squash, some pumpkins
Eastern North America
Quite suddenly, healthy squash or pumpkin plants begin to wilt. Near the base of the plant, small holes may be found exuding beige “frass,” which is created by squash vine borer larvae feeding inside the stem. Squash vine borers are the larvae of a large, orange-and-black hummingbird moth that is commonly seen flying at dusk. Females lay scattered eggs around the bases of squash and pumpkin plants, which hatch into squash vine borers.
Squash vine borers feed exclusively on the spongy material inside squash stems. When multiple borers feed inside a stem, it gradually rots off at the site of most intense feeding.
Use row cover (garden fleece) to protect plants for their first month or so in the garden, or until they begin flowering heavily and need to be visited by bees and other pollinators. In early summer, wrap strips of aluminum foil around the bases of squash plants to discourage egg laying. Among winter squash and pumpkins, varieties classified as Cucurbita moschata are highly resistant to squash vine borers; examples include butternut squash and “cheese” pumpkins.
It is difficult to kill squash vine borers without killing the plants, but it can be done. If you can guess the location of the borers, you can stick a sharp pin or needle into the stem in several places – one good hit and the borer is a goner. You also can use a syringe to inject a Bt or spinosad-based insecticide into the section of the stem where the borers are feeding. Spraying insecticides is of no use because squash vine borers feed inside the stems.