I have been battling it all year due to the heavy rains we've had and an infected punter of seedlings bought.
I eradicated the White powdery mildew on my strawberries and zucchini/squash plants overnight with this:
1 part whole milk
2 parts water
Spray on leaves, don't forget the underside. I saturated mine.
I did this in the late afternoon and in the morning all the leaves were glossy green again without a speck of mildew. And the fruit was back to normal. I couldn't believe it. I did a test patch on the button squash leaves and where I sprayed the leaves were clean and green in the middle of a mildew fest where I hadn't sprayed. It really worked for me.
