Squash vine borer larvae are stocky white caterpillarsthat reach over 1 inch long when full grown. - Clemson University, USDA Cooperative Extension Slide Series, www.insectimages.org

Squash plants attacked by the squash vine borer will go from healthy looking to limp and wilted almost overnight.

They're hard to spot, but eggs of the squash vine borer are tiny, shiny brown disks that the moth lays on the stems, underside of the leaves, and on the blossoms. The best way to prevent borers is to find these eggs and smash them or drop them into a vial of alcohol. Don¹t just brush them off to land elsewhere on the plant or the ground.

Once you've seen the first one, it will be easy to recognize the eggs and distinguish them from little bits of dirt on the stems. The eggs are very tiny, only 1/24 of an inch in diameter, flat, shiny brown, and disk shaped.

The squash vine borers are serious enemies of squash and gourds but rarely attack cucumbers and melons. Named for its boring into stems, the borer’s tunneling often kills whole plants, especially if they attack the base. If you see sudden wilting of plants and sawdust-like waste coming from a hole in the stem, the borers are at work inside.

Borers spend the winter in the soil as larvae or enclosed in cocoons. Moths emerge in late spring and early summer and lay eggs on the stems of the plants, where young larvae can bore into the stems and begin feeding inside. Once inside, they are impossible to control.

Some gardeners have luck performing “surgery” by slitting infested vines lengthwise to remove borers, then covering the slit stem with soil to encourage it to root and renew the plant. It’s important to water regularly at this time.

Because the borers spend the winter in the soil, you can keep from rearing your own new enemies next year by turning the soil in late winter to expose the over-wintering pests to killing cold. Also destroy and remove vines that have been killed. Try to stay ahead of borers by planting as early as the weather allows, since the borers do not usually emerge until late spring or early summer.

Some squash and pumpkin varieties such as Butternut and Green-Striped Cushaw varieties are nearly immune to attack, but others such as Hubbard squash are very susceptible.

You can help protect plants from borers by spraying the stems and undersides of the leaves with Bt, or Baccillus thuringiensis, as soon as the plants begin to grow and continuing spraying throughout the growing season. Bt is an organic-gardening approved pesticide and is not harmful to the bees which are so important for pollinating squash and many other vegetables. Avoid using any pesticides on squash that are harmful to bees; the product label will tell you.