Hi Julie,

Thank you for contacting the helpline with your question. I am sorry to hear about your zucchini crop. The squash vine borer typically lays eggs in mid-late June through early July but can be active as early as May and as late as August. 

If your plants are still alive, you can search for larvae and remove them from the plant. Look for holes in the stem near the soil, usually surrounded or filled by a greenish-orange sawdust looking material called frass. Using a razor blade, cut a slit in the stem and look for the fat, white larvae and destroy it. Cover the slit stem with moist soil to encourage re-rooting. This can be effective since there is only one generation per year.

For next year, if possible, rotate your crops to a new area and keep an eye out for larvae in June. Placing row covers over young plants at this time can help prevent borers (moths) from laying eggs on your new squash plants. Remember, if you are planting in the same area then row covers could actually trap emerging borers that overwinter in the soil. 

Check out this link on the squash vine borer's life cycle, management and prevention:

Squash Vine Borer

I also think you might find this article by Charlie Nardozzi informative:

Vermont Garden Journal

I hope this helps! Please feel free to reach out anytime if you have any other questions.