Answer: What you describe sounds like powdery mildew, a fungal disease that can attack plants when days are warm and nights are cool, and air circulation is poor. Sometimes you can catch the problem at the first sign of leaf damage and remove the leaf from the plant to keep it from spreading. But it sounds to me as though your plants are fully involved so trying to control the problem is probably futile. There are fungicides on the market that you can try, but I think the best thing at this point is to pull the plants up to keep the problem from spreading. You can plant something else in their places. Spinach, radishes, and leaf lettuces are all short season crops and you should be able to harvest them before fall arrives. Best wishes with your garden!
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