Wilting Squash Plants?

Could be the Squash Vine Borer!

Damage first appears as a sudden wilting of a long runner or an entire plant. Closer examination reveals masses of coarse, greenish-yellow excrement which the borer has pushed out from the stem. Splitting the stem cap may reveal a thick, white, wrinkled, brown-headed caterpillar up to 1 inch long and almost 1/4 inch thick.

If only a few vines are present, keep a close check on them. Should any wilting occur, check the base of plants for signs of excrement and borer damage. If there is evidence of borer activity, remove the borer by slitting the vine with a sharp knife and removing the larva. Then cover the injured area with moist soil. Some gardeners put a shovelful of soil at one or more locations along each vine. This is to encourage the plant to develop a supplementary root system and thus overcome squash vine borer attacks at the base.

Once borers have gained entrance into stems, little control is possible; hence, early detection is critical. Excrement should be watched for around the bases of plants, and when first noticed, insecticide sprays should begin. Success of any insecticidal treatment depends on early and repeated treatment. Apply the spray to the stems near the base of the plant and repeat weekly during egg laying periods (early June and early August). Since the insect passes the winter in the ground, squash should not follow squash. Land should be disked in the fall to expose the cocoons and then plowed deeply the following spring. Vines should always be destroyed following harvest to prevent late caterpillars from completing their development.