This particular disease is totally vexing! I admit, I love cramming plants together, especially in a garden. I hate bare soil. I do prune for aeration. I do use free water to wash off leaves early in the day so they can dry by evening. I have used milk; to water plants for more strength (seems to work well) against fungus and virus. I have sprayed with milk. No difference that I could see. I do use mega fans all day and night for aeration. This is a virgin garden and typically all the squash, summer and winter, the cucumbers and tomatoes are always infected. As soon as I see any sign (usually the first cool nights of the summer) I spray with neem oil. It does not stop powdery mildew. Just slows it a bit. I wash vegetables to get rid of any Neem, I hope!
Is there an expert out there that has figured out how to control this fungus?