This is a question often asked by rose growers. In many cases the answer is black spot. Black spot is caused by the fungus Diplocarpon rosae . Circular, feathery black spots occur on the upper surface of leaves. These spots are frequently surrounded by a yellow halo.
Infected leaves turn yellow and fall prematurely.
Sanitation measures are important for controlling black spot. Begin with a thorough clean-up in the fall. Diseased leaves on the ground should be raked and destroyed. All diseased canes should be pruned off. These precautions reduce overwintering fungi.