Won't hurt, will help. Canes/stems have black spot on them, too. Black spot spores are everywhere. The ground needs to be sprayed. You're off to a good start when new growth begins.

Clear out all fallen leaves, and discard them. Then spray the ground and what's left of the bushes. If you're using anything like the Bayer product, spraying every two weeks faithfully, carefully, and measured accurately will do it.