The Q&A Archives: Yellow Squash Plants

Question: What would make your squash plant stalks just all of a sudden start dying?

Answer: If nothing has changed in the way you take care of the plants, I would suspect the sudden wilting is due to squash vine borers. These pesky critters can bore into the stems of the squash vines which disrupts the flow of fluids and causes the vines to wither and die, almost overnight. These pests are difficult to control, but there are the several strategies. You can prevent the vine borer moth (Melittia cucurbitae) from laying eggs on the squash stem with barriers. Or you can go after the larvae with sprays or Bt injections. In May, or 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 a year in the South and they overlap, so it's a problem throughout the summer, says Sams. 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, he says. You can kill the larvae before they tunnel into the plants by dusting the bottom six inches of the stems with an insecticide such as rotenone. Reapply after each 1/2 inch of rainfall, says Sams. If the larvae get inside the stems and you see the sawdustlike frass begin to ooze out, inject Bt 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 because this is where the larvae overwinter.

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