Circular black spots with fringed margins appear on the upper surfaces of the leaves in the spring. The tissue around the spots or the entire leaf may turn yellow, and the infected leaves may drop prematurely. Severely infected plants may lose all of their leaves by midsummer. Flower production is often reduced, and quality is poor.
Apply a fungicide labeled for this disease, following label directions. Avoid overhead watering. In the fall, rake up and destroy the fallen leaves.