Whoa!! That is nasty! Hold off as long as you can before cutting back. Too early removal of the foliage can reduce flowering next year. Ideally, instructions say wait until first frost but if you can hold out until September, you should still get some flowers next season.

Peony nursery that was near my previous residence did their digging and dividing each year some early seeming time like September, maybe even August. During which the current season's stems were cut off. Meanwhile if you look into mildew control there might be something you can apply that will beat it back enough to make it less conspicuous.

Wow thats a doosy! Mine get covered in black spot some years but I dont believe theyve ever mildewed like that. Hopefuly next year it will behave for you!

cut it down in early August.

Yup I am going to risk this.

If it fails to flower I will be my impetus to yank it.

dont suppose i could convince you to just enjoy it as one of ma natures weird shows ... like mushrooms in the lawn .. or some such ...

you know.. we dont have to 'fix' everything ...

it does look kinda cool ... if you can get over what it is ...

if it did it again next year.. id probably get rid of it ... lifes too short.. especially if it pisses you off this much ...

in fact.. why dont you just get rid of it.. its not like there arent Ps that are probably resistant .... im sure it wouldnt be the first plant you edited from the garden.. that you actually liked ... that old love/hate relationship ...

ken

This happens if the Peonies are watered in the evenings or don't have enough room for air circulation. Once it has it, it spreads rapidly. Try and wait until August to trim back, so that you can have a "flower show" next Spring. Remove as much mulch and place new mulch this Fall. The spores could hide in the old mulch. You don't have to remove the Peonies, they are not infected for life...Spraying milk and water mixture helps to stop the spores from reproducing.. google peony white mildew to get more info.

@finafine if poor air circulation is a contributing factor to powdery mildew than for sure this explains my situation as my garden is...."action packed" to say the least ;). I will cut it back when I see August on the calendar

if it did it again next year.. id probably get rid of it ... lifes too short.. especially if it pisses you off this much ...

You have stated it perfectly @ken_adrian Adrian MI cold Z5.

I'm going to recommend this web article I just found. It's not about cutting down, but for future reference managing the outbreaks. https://gardenerspath.com/how-to/disease-and-pests/powdery-mildew-remedies/

Some peonies are more prone to this than others. It began to be a problem/show up about ten years ago. It seems to only affect the appearance and not the health of the plant. Watering foliage does not have anything to do with this type of powdery mildew. It has superseded the older type that plants were made more susceptible to by watering. Air flow seems not to be the reason because I first noticed it in an area where I had created a wind flow tunnel. I have recently been considering if there is a connection beyond the names with the increased use of milky spore to prevent various insect pests as it became more popular about that time.

Interesting thought Mailfleur. Theoretically plants and insects being so different physiologically, it shouldn't be an issue, but there are diseases that have an insect/plant aspect/interface to them. It also floors me with my powdery mildew issues that none of the nearby other plants are affected, only the phlox for me. It's growing right next to older peonies that are unfazed, as are the coneflowers. But we have had a lot of success using milky spore to control our lawn grub problems so there is definitely an association in my yard . . . that's why I sort of love nature, science and gardening. Endless mysteries to be investigated. Although it is also sometimes why I hate them all too . . . :) I had a biology professor once who used to say, "God is in the details" which was a riff on "The Devil is in the details." A little of both sometimes. As Darwin said, "There is grandeur in this view of life."

Edited to add for Rouge that the white allium red peony combination is inspired! Love it. Almost wants me to make space in my own garden for more alliums. I have stuck strictly to the edible ones so far . . .

Rouge that the white allium red peony combination is inspired! Love it.

Thank you @l pinkmountain.

I love alliums and I think the white ones are underused.

When it gets to this stage, may as well cut the foliage off down to 2" of stems. There is no point in keeping these around as they already are too diseased to produce much food for the plant. Either you have a more humid wet condition this year or this variety is more susceptible to PM, I think it is safe to cut down the foliage now without risking loss of flowers next year. You will suffer loss of flowers only if you have to cut down the foliage too early every year. I have done this to my peonies many times but I have not found a decrease in flower blooms the following year. There are some years when PM is particularly prevalent. Maybe that is what happens to your Blaze this year.

When it gets to this stage, may as well cut the foliage off down to 2" of stems.

Now done. (Thanks for the post @KarenPA_6b)