Squash Vine Borer

Yellowish 'sawdust' on the base of plants indicates squash vine borer activity.  Photo by Laura Iles.

Description of squash vine borers

Squash vine borers are a serious pest of summer squash, winter squash and pumpkins.  The squash vine borer is a white caterpillar found inside squash plant stems (usually near the soil line) from June through August. Damage usually first appears as a wilting of the vines. Yellowish 'sawdust' (dry or wet and mushy) may accumulate around the base of the plant indicating tunneling activity by the borers inside. Damage may be severe, but infested plants are often able to live and produce in spite of borer activity.

Life cycle squash vine borers

The squash vine borer begins the summer as a moth slightly longer than one-half inch with a bright orange abdomen with black dots. The front wings are metallic green.  The unusual moths resemble wasps and fly during the day as they visit plants and lay their eggs on the outside of the stems. Small caterpillars tunnel into the plants and remain inside for the rest of the summer. At about the time harvest is complete the borers leave the stems and burrow into the soil to spend the winter.

Squash vine borer adult moth.  Photo by Laura Iles.

Management of squash vine borers

Preventing squash vine borer damage usually requires treating the base of the plants with a residual insecticide spray at the time the moths are flying (early to mid June). Products labeled for squash vine borer will be effective if applied before borers enter the plant.  

Plants that are already have borers in the stem are not helped by insecticide applications. Borers can sometimes be successfully removed from infested stems with a sharp knife during July or early August. Cover the dissected stem with a shovelful of soil.

Other gardening activities that may help reduce future infestations include removing and destroying infested vines as soon as harvest is complete, and tilling the garden soil in the fall and spring to disrupt the pupae in the soil.

Do you live in Iowa and have an insect you would like identified?

Squash vine borer caterpillar within a vine.  Photo by Laura Iles.

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Inse

ct Diagnostic Clinic.  

Squash vine borer female laying eggs.  Photo by Laura Iles.
Squash vine borer eggs are small and difficult to see.  The female often lays them on leaf stems near the soil.  Photo by Laura Iles

Last reviewed:
July 2022

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 13, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.