Usually the best time to prune roses is once a year in the early spring before they break dormancy. And, again a bit later after they are leafing out to remove dead branches from the winter. That's about it except for clipping flower heads. With Black Spot, you'll need to spray with a rose fungicide every 7 to 10 days through, the moist early summer period. Also, be sure to remove all infected leaves and branches and sterilize your pruning shears if you move from plant to plant. Also, never water your roses from above. Black Spot will disfigure your roses, but won't always kill them, BUT I think it's much better to avoid roses that get Black Spot and grow other, disease-resistant rose varieties. Many of the rugosa, shrub and new landscape roses are very resistant to Black Spot. Hybrid teas and floribundas are the types that generally get it."