The following is information on Peony blotch, a common disease of Peony in Delaware.
Peony blotch is now evident on garden and tree peony. Look for purple to dark red spots on the upper surface of the leaves and the corresponding lower surface will be chocolate brown color. The fungus, Cladosporium, will also infect the stems and produce circular spots with red borders. Be sure to remove and destroy infected leaves and stems in the fall to reduce overwintering spores. It's too late for any fungicide control this season unless you are just seeing the first blotches. The disease does not seem to affect plant health all that much, just makes a mess of the leaves.
Information from Bob Mulrooney, Extension Plant Pathologist, UD