Catherine,
Since this plant seems to be particularly susceptible to mildew, you may want to try giving it full-strength milk baths as the very first signs of the proper conditions for mildew formation appear; that is, warm days followed by cool, damp and breeze-less nights (like we're experiencing now). I'd also recommend a couple of doses of seaweed fertilizer during the season to strengthen your plant's disease resistance. I wouldn't give this plant any extra nitrogen. I doubt it needs it, and sometimes higher concentrations of nitrogen seem to exacerbate mildew outbreaks.
My squash are showing the first signs as well, but the milk really seems to do the trick!
