Answer: I've heard gardeners report success in repelling squash vine borers by intercropping with marigolds or garlic so I think it's worth a try. Plant within a few inches of your zucchini plants. I'm not aware of any homemade insecticide solutions for controlling the pests.
The secret to controlling the squash vine borer is to protect the plants during the egg laying time--usually the twentieth of June through mid-July. Once you let the eggs hatch and the larvae bore into the plant stems, the insect is impossible to control. Before the eggs hatch, you have many control options, including:
1. Capture the adult moths as they fly onto the plants during sunny days of summer. In most gardens, only a few female moths are involved.
2. Scrape off eggs before they hatch. Examine plants every day or two from mid-June through mid-July. This takes time if you have many plants.
3. Some winter squash varieties are less attractive to the moths. Check your gardening catalogs for borer resistant plant varieties.
4. Covering the vines with some type of floating row cover, such as Reemay or a similar product which prevents moths from laying eggs on the plants. Put the covers in place when the first moths appear during mid June. Take care to prevent the moths from crawling under the covers and getting access to the plants.
5. Insecticide sprays work if you apply them early and reapply them every ten to twelve days until the moth flight is over in mid July. People often start treatments too late in the season. Few products work well without burning the vines or leaves. Concentrate your spray application around the base of the plant. Bacterial insecticides such as Dipel or Thuricide do not work well because the larvae do not feed on the outside of the plant.
If you use chemicals in your garden, insecticides with carbaryl--often sold under the trade name "Sevin", work well.
If you do not discover the borer problem until the plants wilt, sprays will not work. You can split the stems and remove or destroy worms by hand and cover the vine with soil.
If your plants are wilting, and you cannot find any squash vine borer activity, there may be other causes. A disease called bacterial wilt often affects vine crops, including cucumbers. Walnuts and butternut trees can cause many garden plants to wilt if they are too close to the garden.
Squash vine borer is one of the most destructive garden insects, but you can control it if you protect your plants during late June and early July egg laying season.
Hope this helps!
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