When you water them (I water every 3-5 days depending on soil drainage), try to just water the soil and not the leaves. Before I put in my drip system I would water by just laying the hose down near a plant and leave it on real low for a few hours. It's so much easier to prevent mildew than treat it, but I believe the best organic treatment is what you're using already - neem oil. Although I've used baking soda mixed in water before and that seemed to help as well.

Also, make sure they're getting at least 8 hours of sun (no shade/blocking). Healthier plants seem to repel mildew more, and they grow so fast, it can't keep up with them.

Thanks, I have them in pots (ranging from 15-18 inches) with supports and some have grown really tall (all the way to the top of the supports) while others seem to be more of ground spreading type (really big leaves rather than long lengths of vine). This is my first time growing different types of squash (zucchini, scallop, kabocha and an Asian variety). When they were small, I used a sprinkling watering can but now I just use one with an open spout on one end and try to avoid any leaves.

What I should have done was to continue to use Neem oil after my first treatment, but that single treatment in April seemed to have done the trick, but now that I recall, it got really hot and sunny after that treatment and that is probably what helped more than the Neem oil. It was the last few days of relatively low temperatures and cloudy skies that seems to have re-energized the mildew. The current problem is on the lower leaves which are shaded out by the upper leaves. Will have to hit them with Neem oil every week I guess.

I have used a milk and water spray that worked well.