Occasionally, it is a serious problem on susceptible cultivars of red and black raspberries, especially the varieties Latham and Black Hawk. The disease is caused by the fungus, Sphaerotheca macularis. The fungus overwinters in infected cane tips and dormant buds. The characteristic sign of this disease is a white, powdery growth, primarily on the underside of the leaves.
Infected leaves are dwarfed and twisted and have a yellow appearence on the upper surface.
Powdery mildew is favored by warm weather without rainfall and is most serious in years and in plantings where there is poor air circulation. Disease Management Plant disease resistant cultivars when possible. Avoid the cultivars Viking, Ottawa, Latham, and Glen Clova. Chief, Marcy, and Malling Orion are resistant and Logan is immune. Removing suckers that are infected with powdery mildew and pruning canes in the spring to a desirable height may reduce sources of the disease.