Here in the Pacific Northwest we have a lot of trouble with blackspot on roses. I've learned that it's important to pay attention to the roses in the winter.
During the month of December I strip all the leaves off my rose bushes and trim them back. I pay close attention to trimming out all black spotted stems, even if it seems as if I am destroying the rose bush. It's so necessary. If you leave black spot on the stems, the buds will be affected and will not be beautiful. So, I am BRUTAL.
I also clean the ground around my roses. Do not leave any cut stems or leaves. Be meticulous. So far, my rose bushes have grown back just fine. I prune the roses back to about 20", leaving 2" for possible winter damage. Then, in the spring, I go back and trim them to about 18".