Rose black spot is a fungal disease of plants. Purple or black spots develop on the leaves of rose plants, and the leaves often turn yellow and drop early. This affects the growth of the plant because photosynthesis is reduced.
The fungus is spread in the environment by water or by wind. Water splashing from leaf to leaf, or wind carrying the fungal spores, moves the infection from one plant to another.
Rose black spot can be treated by using fungicides, and/or by removing and destroying the affected leaves. Destroying the leaves removes the source of the infection, so less of the fungus can spread to healthy plants.