These fungi lurk all winter in the dried peony leaves that collapse in a circle around the plant. May. The combination of fresh flowers and dead leaves is not what you are seeking from peonies. To delay peony leaf blotch, or even prevent it entirely, cleanup is essential. Within the next week or so, clip off the old stems at the soil line and rake them clear of the peony bed. This simple step removes almost all of the surviving fungi, so they can't overwhelm the new shoots.
Irises also appreciate a cleanup.
Many varieties of German, or bearded, iris fall prey to iris leaf spot, a fungal disease that produces rounded, wet-looking, brown spots on leaves and eventually turns the entire leaf brown. Wet weather and no cleanup equals sick leaves when the irises bloom. Cleaning up an iris bed calls for a pair of stout shears or scissors. Clip off the old leaves at the base and rake them out of the bed. In fact, German irises are better off surrounded by bare soil than dead leaves.