I have a peony plant that is heavily damaged with what I think is Botrytis. My other peonies have only a few spots and damaged buds that can be removed. First the heavily damaged plant, will it survive if I cut it back to the ground, or should I just pull it out? It is being crowded out by indigo and I had planned to transplant it in the fall. It has failed to bloom even though it it is 3 or 4 years old.
I’d start treating the less=affected peonies ASAP with a fungicide. It is possible for the worst one to survive but I’s rip it out and remove it from the area as a precaution. Bag it and get it off the property. It has been a damp spring and the fact that it was getting crowded by other plants was the perfect set up for botrytis to take hold. Peonies need space, and full sun, and good air movement to thrive disease free. Obviously keep mulch away from their stems and avoid spray watering from sprinkling systems. Here are some links you should find helpful:
http://plantclinic.cornell.edu/factsheets/botrytisblightpeony.pdf
http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/fungal-spots/botrytis-blight-of-peony.aspx
https://pnwhandbooks.org/plantdisease/host-disease/peony-paeonia-spp-botrytis-blight