Spores are produced by the tiny black fruiting bodies and are splashed by rain and infect the canes if they remain wet. A second type of fruiting body is produced on old canes in spring, releasing spores that can be carried for long distances on the wind.
Infection invariably occurs through a wound to the cane. The wounds can be caused by a number of factors, including pruning damage and frost cracks. The fungus invades frequently through areas of feeding damage caused by the raspberry cane midge. When this happens, the disease is often referred to as midge blight.
Poor soil conditions, such as waterlogging, weaken the plants and make them more susceptible to attack. The fungus is able to survive for some time in the soil on buried raspberry wood.