Good morning! My question is regarding my peonies. By this time of year, powdery mildew has completely covered them, despite my efforts to get rid of it.
They grow well, bloom beautifully, but by now are covered with mildew. Help!
What can I do this fall to make next year better?

Welcome to the site!
It just needs more air movement, and some seem to be more susceptible than others.

You can spray proactively, before the problem actually shows up, with something like this product: https://www.johnnyseeds.com/to...

Powdery mildew is so ugly, isn't it??!! Absolutely hate seeing it.
Some things to check and be aware of that can cause mildew. Over fertilizing, watering the foliage, not enough space between plants, too high/low soil ph and possibly mulch too close to the plant in damp areas.
Another thing you might try is a milk/water spray in late spring before it shows up next year, repeated every few weeks. Have read good things about doing the same with baking soda if soil acidity is high. Copper based fungicide would be the next step up.

I noticed powdery mildew on my herbaceous peonies only if they had been isolated. As long as there has been some ground cover around them, or if they had been planted closer together, powdery mildew has never been a problem in my garden These are pictures taken today