R. Stace-Smith, Bugwood.org
Many blackberry varieties remain symptomless when infected. Symptoms of infection by the leaf curl virus gave rise to the disease name. The leaves on infected canes are stiffly arched or curled downward. Leaves of red raspberry become yellow, while those of black raspberry take on a dark-green, greasy cast. Clusters of stunted lateral fruiting shoots arise from single nodes on the canes. The canes are stiff and brittle, and the fruit small and crumbly. Symptoms on red raspberry are very mild or might not appear until the season after infection. This virus is spread by aphids and petiole grafting.
Two different strains of this virus exist, with one strain infecting red raspberries and the other infecting black raspberries. Both infect blackberries, although most varieties are symptomless. This virus is spread by at least one species of aphid. Spread of the virus is slow. Control includes the standard practices of starting with clean stock, keeping plantings from wild raspberries or infected plants, and roguing plants that show symptoms. Using insecticides to control aphids also slows the spread of this virus.