Blackspot is a common problem associated with growing roses, especially in the south. Blackspot can be identified by thoroughly looking over your roses. Look for small blackspots that may be accompanied with yellowing of the leaves and leaf drop.
You should treat roses at the first sign of Blackspot to keep it from spreading. Be sure to treat the soil, mulch and anything else near the infected plants. Always water plants from the base to insure you are not spreading the Blackspot with water. Splashing, trickling and running water are all common reasons for the disease spreading to other plants.
Since it spreads rapidly, always be sure to discard any rubish that contains leaves, stems or blooms from a plant with Blackspot.