It sounds as though your rose is infected with powdery mildew, a fungal disease spread by the wind that causes curled, discolored, distorted foliage and sometimes kills infected leaves and canes. Typically, powdery mildew crops up when rainfall is low, days are dry, nights are humid, and average temperatures range from 70-80°F. As soon as symptoms appear, spray the plant with a fungicide specifically designed for roses (available at most garden centers). Repeat applications every 7-10 days if mildew recurs. Also, be sure your rose has adequate airflow. If not, remove any crossed canes and any congested stems in the center of the bush. Rake up and dispose of fallen rose foliage in autumn. In the future, plant rose varieties that are resistant to powdery mildew.