Squash Vine Problem Becoming Common

Is it just my imagination or did gardening have less problems 50 years ago? Oh, we had the occasional cutworm that we fought with Folgers Coffee cans around each young tomato plant, and we were on the lookout for potato bugs. But squash was easy – you planted, it grew. Well, those days are long gone. More gardeners are finding it difficult to keep squash vines healthy enough to produce a crop, and squash vine borers are to blame.

Gardeners first notice that something’s wrong when leaves wilt, as they sometimes do on hot, dry days. They might perk up a little after watering, but eventually they remain wilted and quickly go downhill.

Squash vine borer problems often go undiagnosed, because the vines wilt and collapse in mid-summer from no apparent reason as the borer is safely nestled within the stems, hidden from view unless the stems are dissected. It’s become an increasing problem in winter squash, zucchini, pumpkins and less frequently in cucumbers and melons.

The adult wasp-like moth is dark gray with an orange abdomen and makes a noticeable buzzing sound as it flies. The moths lay eggs at the base of plants in late June. As the eggs hatch, the inch-long, cream-colored, brown-headed larvae enter stems, tunneling throughout and causing vine collapse. After feeding for about four weeks, larvae exit the stems and enter the soil where they survive winter until next spring when they emerge as adults, beginning the cycle again.

Adult Squash Vine Borer Moth
Eggs laid by adult moth that will hatch into borers.
Borer inside stem

To control squash borers:

  1. Apply insecticide spray or dust containing carbaryl (Sevin), spinosad or permethrin to the base of plants around June 20 and repeat in seven days. The insecticide must thoroughly cover the stems below the leafy canopy, especially the twelve inches above soil level. The insecticide kills the newly hatched borers as they attempt to chew their way into the stem. Spraying the leaves isn’t effective. Thorough coverage on the stems is the key.
  2. Besides insect sprays, aluminum foil can be wrapped around the basal twelve inches of stems to prevent borer entry.
  3. As vines grow, cover stem sections with soil in several places. As they root, the chance that borers will affect the entire planting will be reduced because the plants are rooted in more spots.
  4. Remove and dispose of all vines in the fall, or earlier if they collapse and die.
  5. Rototill the garden in late fall just before freeze-up. If the insects overwintering in the soil are exposed to severe cold, chance of their winterkill is increased.