Iowa Insect Information Notes

Squash Vine Borer

Squash Vine Borer

by Donald Lewis 

The squash vine borer is a very common, pudgy, 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.  Other times, moist, white sawdust 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.

 The squash vine borer begins the summer as a moth.  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.

 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).  Sprays provide a much better barrier against borer attack than do dusts.  Home gardeners can apply Sevin, permethrin, bifenthrin, esfenvalerate, spinosad or other labeled home garden insecticide.  Commercial vegetable growers can use one of the following insecticides: Ambush 25WP, Asana XL, Capture 2EC, Endosulfan 3EC or Phaser 3EC or Pounce 3.2EC.

 Plants that are already infested 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.

Updated 08/13/2007 - 1:50pm