The Q&A Archives: squash vine borers

Question: I need to know how to prevent them. They have devastated my zucchini for the last 2 yrs, I even planted them in different areas of my garden, but didn't do any good. Thanks

Answer: 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 so it's a 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. 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. 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 where the larvae overwinter.

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