I've been lucky so far. I have seen no signs of powdery mildew
yet in my garden, which is an absolute rarity for the month of July in Michigan. But, I just know it's coming, and I've gotten a few questions about it from other gardeners. The good news about powdery mildew is that if you catch it early, you can stop it from spreading and having an impact on your plant's overall health. The first step to stopping powdery mildew in its tracks is to remove any infected foliage and throw it away (DON'T compost it!)
Once that is done, mix up a batch of my powdery mildew spray. It couldn't be easier: water, baking soda, vegetable oil, and dish soap. And it is much cheaper than buying a fungicide at the garden center!
You'll have to spray once a week to keep powdery mildew at bay. Be sure not to spray in full sun to avoid burning the foliage. I use this in my own garden every year, and it really works well.