Good News!

Taken from the link below:
Peony Wilt

Tree peonies rarely suffer problems from pests and are unpalatable to rabbits and deer. The only disease you are likely to encounter is peony wilt. This may appear in early spring, usually before flowering. There are no longer any chemicals with label recommendations for the control of fungal diseases on tree peonies. Good hygiene and cultural practices are the key to preventing and dealing with fungal attack. Maintain a good air flow around the tree peonies by not overcrowding them with other plants, particularly at ground level.

The fungal spores of peony wilt can over winter on old foliage so its important to pick up and burn old leaves in the autumn. With deep planting, good hygiene and regular observation, although peony wilt may appear occasionally, it rarely causes serious damage to a mature plant.

Good luck to you!

Sue

Here is a link that might be useful: Care of your tree peony