My rose bush!
It's hard to tell from your photo exactly what is happening, but both rose slug sawfly larvae and black spot disease are common problems in our area.
The leaves at the the top of your plant look unaffected. If there was disease in the lower leaves, it is now important to clean up all the fallen leaves and dispose of them out of the garden. This will lessen the chances for black spot to spread.
Here is a page about rose slug sawflies. They and Japanese beetles are the most likely culprit pests of leaves during the summer: