Answer: It sounds as though your plants have fallen victim to squash vine borers. Just as squash is beginning to flower in your area, the adult moth lays eggs on the stems, usually within six inches of the ground. The eggs hatch and the larvae tunnel into the stems to feed for four weeks, which eventually causes the plants to wilt and die. There are two generations of moth/larvae a year and they overlap, which makes this a bigger problem throughout the summer. Prevent the moth from laying eggs by wrapping the stem with a barrier such as aluminum foil or covering the whole plant with a floating row cover until blossom time. If you use row covers, keep the plants well watered. Squash plants tend to dry out quickly under them. If the larvae get inside the stems and you see the sawdustlike frass begin to ooze out, inject Bt (Bacillus thuringiensis) into the stems with a garden syringe about 1/2 inch above the soil line every two weeks, starting after first flowering. If you miss some of the borers, slit the stem, remove the larvae and replant the slit stem. In fall, remove and destroy the squash plant debris where the larvae overwinter. Bt is an organic pesticide which is basically a disease you are giving the squash borers. It isn't harmful to you, birds, bees, pets, etc. It is widely available in garden centers and mail order gardening catalogs. It is often sold under the brand name Dipel or Thuricide.
Be sure to plant your squash in different areas of the garden each year. Rotating crops helps keep the soil healthy and it confuses the insects!
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