For you to have continuing problem with botyris and other fungus with your peonies your growing conditions must not be ideal for peonies. For you to succeed I think you will need to devise a preventive spray and sanitary program, at least for your peonies and perhaps for the rest of your garden, which may be a fungus incubator. Al

This is typical tree peony behavior around here, and it does have to do with our summer heat and humidity, but it's usually harmless. The growing season is much longer than necessary, so the foliage tends to give up pretty early on. The best plan is to remove the leaves at the axil (where they connect to the stem), leaving all stems intact for now. Any buds that don't leaf out in spring can always be cut back then, but it can be hard to tell at this time of year which are viable and which are not. It's a good idea to throw the leaves in the garbage rather than the compost, to avoid perpetuating any fungus spores from year to year. One other lesson I've learned is that tree peonies are very susceptible to overwatering, especially if done too frequently - they're from the mountains and like good drainage. Sprinklers can kill 'em faster than anything, especially if they're set to water a lawn, etc.

Thanks for your replies. I think I need to stop thinking of my tree peonies as peonies, and as their own kind of guys with different problems and solutions. And I'm tickled the different reactions based on Zonage - USDA 9 Ca 15 is going to have a whole lot less fungi than those of us in the Mid-Atlantic. Its good to know about not over-watering. Lately I've been thinking "I love those tree peonys so much. I'm going to be sure to give them plenty of water." So thanks.