The Purdue Plant and Pest Diagnostic Laboratory

P&PDL Picture of the Week for
August 20, 2007

Peony leaf blotch

Karen Rane, Sr. Plant Disease Diagnostician, Department of Botany & Plant Pathology, Purdue University

Leaf blotch, also called red spot and measles, is a common disease of peony caused by the fungus Cladosporium paenoiae. The disease has multiple names because there are multiple symptoms -  lesions occur on leaves or stems, and vary from tiny red spots (“measles”) to larger brown or purple blotches. The fungus survives the winter in infected plant debris, and produces spores in the spring which are splashed onto young foliage and stems through rainfall or overhead irrigation. Although symptoms are quite striking, and infection can be very severe, the impact of this disease on plant health and survival appears to be minor. 

Sanitation (removing dead plant residues in late fall or early spring before plants break dormancy) is important in reducing the severity of this disease in the home garden. Use drip irrigation rather than overhead sprinklers when watering peony plants, to avoid wetting the foliage and providing a favorable environment for disease development.

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Peony leaf blotch

Peony leaf blotch

Peony leaf blotch

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service