Sudden wilting of squash plants is a sign of the squash vine borer. The squash vine borer is the larvae of a black moth orange-red markings. It has a wing span of about 1 - 1 ½ in. (25 to 37 mm). The moth lays its reddish-brown eggs on the squash leaves. When they hatch, the larvae bores its way into the stem, usually in the lower 1' of the stem.
Signs of Squash Vine Borer DamageYou can often see a small hole and some frass that looks like sawdust. The injury can girdle the stem and prevent the plant from taking up water and nutrients, causing it to wilt and ultimately to die. Multiple borers can be found in one stem.
Plants Affected by Squash Vine BorersFavorite hosts of the squash vine borer include: hubbard, zucchini, pumpkins and gourds, although other squashes may be effected. Squash vine borers don’t usually attack cucumbers and melons.
Controlling Squash Vine BorerSince squash vine borers over winter in the soil as larva in cocoons, removing the spent vines after harvesting and tilling the area will destroy any larvae still in the vines and lift any that have made it into the soil. The birds will take it from there.
If you do see signs of squash vine borer:
- In the spring, the first mode of attack should be to monitor for eggs. If you can remove the eggs when they appear, you're half way there.
- The larvae usually bore into the stem where it meets the ground. Wrapping some foil around this area acts as a barrier.
- If you do see a vine wilting or notice a hole at the base, it's still possible to save the plant by making a vertical slit into the stem and removing the larvae by hand. The plant will heal. You can cover the wound with moist soil to promote more roots.
- And finally, you can pile some moist soil over the leaf joints near the in ground stem. They will root. So even if the stem is damaged, the plant won't die.