Every year that we have planted yellow and zucchini squash we have had problems with the squash vine borer. The moth (pictured below) lays its eggs on the vine or under the leaf of squash plants. When the egg hatches the grub moves into the vine and feeds on the inside of the plant. Most of the time you don't realize the grubs are there until it is too late. One day you walk out and see your beautiful plant fallen over on its side.
Here's a picture of the inside of the stem. If you look closely you can see the small white grubs with black heads. Those are the pests!
The eggs are so tiny but if you look hard on the base of the plant you can see them.
Once the grub is done eating it moves under ground to complete its life cycle and later emerges as a moth.
We have tried several things to get rid of the pests. Two years ago, we ordered some beneficial nematodes from Planet Natural that we applied to the soil. The nematodes attack and hopefully destroy or at least decrease the population of grubs that are in the ground. This year we will be applying BT to help fight the tiny pests. BT (Bacillus Thuringiensis) is a safe alternative to regular pesticides and insecticides. Agorganics has a great article on the benefits of using the product. You can find BT locally at garden centers or order it online.
Some people I talk to have completely given up growing these summer squash. Well, we haven't done that yet. We are growing a few this year. The good thing is that even if your plants become infested with the bugs you can usually get some fruit before total destruction.
We have found that butternut squash are not as susceptible to the pests. Another winter squash that our seed catalog claims to resist the vine borer is trombone squash. We are growing those for the first time this year.