How to Control Squash Vine Borer
Squash vine borers are terrible pests of the cucurbit family of plants that include squash, zucchini, pumpkins, melons, and cucumbers.
The larvae of the squash vine borer, drill into the stem of a cucurbit plant, and eventually cause the rest of the plant beyond the base of the stem to die. This actually happens rather quickly, and by the time the damage is noticed it is usually too late.
The adult squash vine borer is actually a moth that emerges in the spring to deposit eggs on the plant. The adult black and orange moth flies during the day and can be mistaken for a wasp. Eggs are circular and dark reddish brown in color. They are typically laid at the base of the plant. After hatching the dreaded larvae of the vine borer drills into the stem of the cucurbit plant. These insects are so successful that as few as 10 moths could theoretically infest all the cucurbit plants planted on an acre of area. The larvae will feed for 4-6 weeks, leaving behind a brownish-orange excrement called frass. If the plant dies before the larvae is mature, it will simply migrate to another cucurbit plant. So, if you have an infested cucurbit plant, it is wise to dispose of it. The larvae are white with a brown head, growing to a length of about 1 inch.
1. Crop rotation is helpful, but not perfect, because the adult can fly.
2. Quick removal of infested vines will help reduce populations.
3. Using a razor blade to slice into the stem to find and dispose of the larvae has been found to be effective. Usually the larvae reside in at the end of the frass, where the stem is still green.
4. The bacterial insecticide, BT, can be injected into the vines.
5. Planting cucurbits later in the season can be helpful.
6. Companion plantings of marigolds and nasturtiums can help bring in predators, and act as a repellant.
7. Catnip can be cut and placed around the plants as a repellant.
8. Having good soil always helps.
I personally don't do much at all for squash vine borers. I do quite a bit of companion planting and crop rotation which helps, but I still get some squash vine borers. They shorten my zucchini season, but by that time, I'm sick of zucchini anyway. I do get the infected vines far out of my garden. The rest of my cucurbits seem to cope okay.
Thanks to Mark Hoffman for the great pictures.