I have a peony, Dancing Butterflies, I planted 2 yrs ago. It bloomed this spring and is now covered in a powdery white looking stuff. It is covering almost all the leaves. The other peonies in the garden do not have it. It is planted by itself, nothing around it, so very open. I would like to know if anyone knows what it is, and how to get rid of it and if it just looks bad or will it actually kill my plant?

Sounds like mildew to me but I've never had an issue. Is that peony in a crowded bed or somewhere it's getting hit by a sprinkler or something? I'd certainly treat it if you think it's mildew and make sure it's watered at the ground, not on the leaves. Hopefully someone else who's seen the problem will answer with a specific thing to use, sorry not to be more help.

One of my friends' peony garden was hit by powdery mildew last year. It is relatively harmless just unsightly. There is a recipe for a spray involving milk that you can find on the Internet for an organic control.
Does this afflicted peony sit in a spot without good air circulation? You may want to move it in the Fall if it does or cut back encroaching plants.

One of my friends' peony garden was hit by powdery mildew last year. It is relatively harmless just unsightly. There is a recipe for a spray involving milk that you can find on the Internet for an organic control.
Does this afflicted peony sit in a spot without good air circulation? You may want to move it in the Fall if it does or cut back encroaching plants.

Some peonies foliage are more susceptible than others. In esp. rainy and humid weather, some peonies will get PM faster than others. Like Liz and LG noted, it is harmless to the peony. Since your peony has it bad, I would just go ahead trim down the foliage.

The peony is right out in the open and not touching any other plants. It was just planted 2 years ago so not very big yet, very open around it.
I know it won't hurt to trim the foliage, but I wasn't sure since it just bloomed a couple weeks ago, Ive never trimmed them back that soon after blooming.

If the foliage is still green, it is producing food to feed the roots and form next year's flowers.

I agree with LG, if you can treat the plant and remove the mildew I'd leave it to go dormant naturally in the fall. It certainly won't kill the peony to be cut back now but your growth next spring will be much less than it would be if you can get the foliage healthy again and leave it.