Latin name: Cladosporium paenoiae

Common name: Peony Leaf Blotch

Plant family: Peony

Date/Location of specimen: https://www.ppdl.purdue.edu/PPDL/images/peonyleafblotch2.jpg

Description: Leaf blotch, also called red spot and measles, is a common disease of peony caused by the fungus Cladosporium paenoiae. 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. 1 The leaf spots are glossy and purplish-brown on the upper sides of leaves. On the lower sides, spots are chestnut-brown. Infection is generally more pronounced at the margins of outer leaves. Leaves may become slightly distorted as they continue growing. 2

Fungal infections on young stems first appear as elongated, reddish-brown streaks. As plant growth continues, infected tissue near the crown may darken and become depressed. Stems on the upper portion of the plant may show individual, raised spots.

Control: 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. 1 To manage peony leaf blotch, cut the stems at ground level in the fall or early spring. Rake the area before new shoots appear. Fungicides are available to help control the disease, but must be used in combination with other management practices. Also, providing good air circulation and avoiding wetting the leaves when watering can help reduce disease severity. 2

References:
1 https://www.ppdl.purdue.edu/PPDL/weeklypics/8-20-07.html
2 http://www.ipm.iastate.edu/ipm/info/plant-diseases/peony-leaf-blotch

Collection Sample #3 of 5 DISEASES

Master Gardener Class Horticulture Portfolio