Unless your plant is a tree peony it will be going dormant in a couple of months and you should cut off the foliage so don't frete. Powdery mildew is a natural it lives on all of the surfaces you have around you. Look at your plants and see if they are too close to other plants. Peonies do get powdery mildew but good air circulation will help. do a search on this group for mildew one of the suggested treatments was diluted milk.

Sorry, not me. That's at least 1 advantage of living in such an arid state, no plant mold or mildew issues.

Powdery mildew growth is favored by cooler temperatures (60-80*) and humidity, especially at night; it is hampered by temperatures at 90* and above. I don't know about your local conditions, but we have been having delightful weather this June - cooler than usual, just now heating up into the 90's, but still somewhat humid ... perfect for PM, which I am seeing earlier this year on the more susceptible cultivars. My peonies generally don't show symptoms until later in the summer when the temperatures are beginning to moderate a bit, especially in the evenings, but humidity is still high. I'm just guessing that earlier in the season, the younger foliage is perhaps more resistant to the fungus. In any event, once the leaves are seriously affected, I cut them down to the ground. Once they've lost their green color, the chlorophyll is gone and they're not able to contribute anything to the root system anyway. Sure, there's a bit of a hole in the garden, but not for long, as other plants soon fill in the empty space. And they always come back beautifully the following year. Shady conditions also promote PM; is the plant getting as much sun as it was in the previous location? Checking on the watering is a good idea, but, finally, perhaps your plants need a little time to get adjusted to their new home and are just a little less resistant until they do so. Best of luck - I'm sure this peony has great sentimental value to you!

Sorry Whitney, don't get over here often anymore! Cold impacts different peonies in different ways--the vast majority aren't injured by cold unless it gets down into the 20s. Once the buds have formed on most of them though the buds are more apt to be damaged by cold. The only ones that don't seem to be impacted at that point are the very early species peonies. There is also another peony forum on www.garden.org that is more active if anyone is interested. Also free and also a nice group of avid peony growers! If you don't get a response quickly on one forum try the other; there are also several great peony groups on Facebook as well. Planet Peony is a favorite and we also just started a new one--American Peony Society group. I will warn you, though--it can be fatal to your wallet to see all of the gorgeous pics shared there!