Roses in the landscape are subject to this disease annually. Several spots may coalesce to produce irregular lesions. A yellow halo may form around the spots, then the entire leaf turns yellow and drops off. Defoliation weakens plants and reduces flower production and quality. Canes may also become infected.
Lesions appear as raised purple-red irregular blotches, later becoming blackened and blistered.
Wet conditions of at least 7 hours with temperatures between 60-80 C are required for infection. Proper sanitary practices are essential, because the black spot fungus overwinters on infected plant material. Gather and destroy fallen leaves. Remove old infected canes by cutting them back as severely as possible without cutting too close to the graft. Plant roses far enough apart to allow good air circulation between plants.