Anya, I moved some part of the soil from the top and replaced it with chicken grit and poured some fungicide a couple of times. I would probably suggest if it does not work and the plant is not healthy pulling the root in the fall, cut rotten parts, soak in water with fungicide for a few hours and plant it somewhere else with good drainage. Personally I would do it, but only if I treasure this particular peony and do not have a lot of other things to worry about.
