What disease are you trying to control in your peonies? Botrytis Blight? Powdery Mildew? Make sure your peonies have good air circulation, are in well-drained soil, and receiving sunlight. Also, follow good sanitation practices, such as removing dead or infected blooms and buds. Dip your pruners in 70% rubbing alcohol or 10% bleach solution between cuts. Fungicides that can be used on peonies to control disease include 'Chlorothalonil' (Daconil), Maneb, Mancozeb or Copper. Be careful using copper, and never use it when temperatures are above 85 degrees. It can burn or cause damage to the plant when temperatures are warm/hot. Spray the plants with a fungicide when young tips break through the ground. Follow 2 weeks later with another application and every 14 days thereafter until mid-June.