The Mildew Cure I posted the link to earlier, works really really well on powdery mildew on squash. It's what I bought it for originally. There's baking soda in it, also garlic and some other things. Squash grow so vigorously that I've never lost a plant that I've treated.

Hoping my plants can hang in there until I get back into town - they needed sprayed before we left on Thursday, but it was pouring down rain -