There are a number of diseases that affect squash that have the same symptoms and since I can't see your plants I can't be sure which problem you might have. They could have died from Bacterial Wilt, Squash Borer, or something else. I would look closely at your plants to see if you can see any striped beetles. If you have them on your plants, they probably died of blight since those beetles spread the disease. In the end, all of these diseases are fatal to your plants and the only way to avoid them is to remove all diseased foliage and to spray or dust your plants with an insecticide every 7 days through the growing season. You can find organic sprays or chemical sprays to do the job. Just be sure to use one that will keep cucumber beetles and squash borers at bay."