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Cercospora leaf spot (Mycosphaerella confusa) is a frequently occurring fungal disease that infects both blackberry and raspberry. The disease begins as circular, reddish-purple spots on leaf surfaces, later becoming irregular or angular. Centers of spots turn white to gray, while margins remain purple. Spots may drop out, leaving a jagged or shothole appearance to leaves. Leaf spots may resemble anthracnose. In severe infections, leaves can turn yellow and drop. The fungus overwinters in fallen leaves and potentially in other host plants. Young, expanding leaves are susceptible to infections in spring. Secondary infections can occur throughout the growing season if conditions are rainy.

Cercospora leaf spot on blackberry leaves.

(Photo: Brenda Kennedy, University of Kentucky)

Close-up of spotting.

(Photo: Brenda Kennedy, University of Kentucky)

Fungal reproductive structures as viewed under magnification.

(Photo: Brenda Kennedy, University of Kentucky)

Management: 

• Increase air circulation to encourage drying of plant tissues (pruning, thinning, spacing).
• Manage weeds through herbicide applications, mowing, or soil cultivation.
• Apply fungicides.

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