I don't know that it is a disease. I would like more details of how it was planted, and what it looked like coming out of the pot. How it has been watered since planting. Al

I've had similar burned looking leaves on peonies that I accidentally planted too deep, although they typically start shriveling, too. I dug them and replanted higher in the fall and they were fine the next spring. Could yours be the same thing or are they actually diseased rather than stressed?

It was fine when I planted it and it had several blooms.There were alot of small buds that turned black and didnt bloom. I bottom water... Weve been getting a lot of rain here in Ny lately..I havent mulched yet ...or fertilized since planting ..I think I added store bought compost and some ocemote when I planted...Ill double check but I think I planted at correct depth ...hmmm

I do not often buy a blooming peony, but when I have they have been terribly root bound in the pot. In which case I am faced with keeping it in the pot and watering everyday just to keep it alive, or planting in the ground, scoring the rootball as much as possible and watching it suffer the stress, much as yours has. In the fall I dug them up and divided to replant a reasonably good plant. The small divisions saved did not survive in the spring. A big blooming peony at a reasonable price is not always a bargain. Al

If you planted this year why not just return it?