I'm in Illinois, but it is obviously very hot and dry here, too. I think my field of pumpkins and melons has a lot of powdery mildew, which is typically associated with overly wet weather. However, there is a strain of powdery mildew that typically lives in the desert southwest, and it thrives in hot and dry conditions. I think that's what I have, and maybe you too.
Daconil is meant to coat and protect the healthy leaves you have left. Two other treatments that I have read about, but not tried, are milk and peroxide. The milk is a 10-20% solution of skim milk and water. I think it works by changing the surface ph, making it hard for the fungus to survive, but that's just a guess. Hydrogen Peroxide will kill anything bad that it touches. Dilute the drugstore peroxide in 2-3 parts water.
Your other options would be fungicides with either a copper or a sulphur base. You could try all of these in a five-day rotation.
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