As a rule, peonies are exceptionally free of disease. The only diseases that cause significant damage to peonies are leaf and bud blights caused either by fungus Botrytis or Cladosporium. As with most fungus diseases, the best preventives are sanitation, disposing of old leaves in the fall, and providing adequate light and ventilation. Spraying with a copper sulfate and lime fungicide like Bordeaux mixture, is effective when used as soon as new growth emerges, and again at least twice during the growing season, or at the first signs of infection. Leaves may show spots, yellowing and eventual withering, while buds will often appear distorted and will dry and fail to develop.