Infected leaves turn yellow and fall off prematurely. The fringed margin and black color distinguish this leaf spot from others. Infections on canes are identified as reddish-purple spots. Splashing water spreads blackspot. Infection occurs after leaves are wet for several hours, making it more serious during rainy periods.
Some roses are less susceptible than others, so cultivar selection is important.
The fungus overwinters in fallen leaves and stem cankers. Raking and removing these leaves in the fall may help provide some control. Avoid wetting the leaves when watering and locate plants where there is good air circulation. Fungicide spray programs need to be started as soon as new leaves appear in the spring. Mulching also helps keep water from splashing up onto the leaves.