P&PDL Picture of the Week for
June 14, 2004

Rose Spot Anthracnose

Karen Rane, Plant Disease Diagnostician, Botany & Plant Pathology, Purdue University

The lesions on the leaves of this shrub rose (Figure 1) are the symptoms of spot anthracnose, caused by the fungus Sphaceloma rosarum. This fungal disease may not be as well known as black spot on roses, but it can cause significant spotting on susceptible cultivars. Initially, lesions are small, round, reddish-purple spots. The centers of the spots eventually turn gray or white, with red margins (Figure 2). Tissue may drop out or crack in the center of the spots, giving infected leaves a shot-hole appearance. Lesions can also develop on petioles and stems. The fungus produces microscopic spore-bearing structures in the lesions, and spores are spread from plant to plant by splashing water. Like other fungal leaf spot diseases, spot anthracnose is favored by long leaf wetness periods. Proper plant spacing, good weed control, and using drip lines or soaker hoses rather than sprinklers for irrigation are management practices that should help to reduce this disease. Fungicides labelled for control of black spot of rose are also effective in managing spot anthracnose.

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Figure 1

Figure 2

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service