Q: What are the reddish brown spots on the leaves of my peony? A: These spots are most likely to be caused by some sort of fungal disease. Peonies are subject to a number of fungal diseases that tend to thrive in cool, wet weather. There are several fungi that could be the cause of the problem but most likely that it is due to Cladosporium or peony measles. This fungi is often seen after flowering and it attacks the leaves and stems. The spots start out as small red lesions (hence the name measles) and eventually coalesce into dark necrotic spots. Cladosporium will not likely kill your plants. It is a good idea however to cut down the foliage around the time of your first hard frost and remove it from the garden.

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