Black spot is probably the most common and serious disease of roses in Kentucky. Black spot is a problem both in greenhouse production and outdoor plantings. 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.