Knockout Rose Bush Leaves Have Holes And White Spots

Q: Have a huge knockout rose bush with holes in the leaves and the leaves are covered with white spots. Full of roses but the flowers don't last long...can I prune now and then treat, or do I need to wait until fall? Thanks.

A: You may cut it back now. Just be sure to keep it well watered. The white spots may be powdery mildew, the holes are probably rose slugs. You will need a fungicide and a pesticide. Best And Happy Yardening, Nancy.