Looks like a case of leaf spot (aka Cercospora Leaf Spot), a very common fungal infection. Typically caused by overhead watering and the presence of the fungus. Becomes "visible" at the end of Summer or in the Fall. Looks bad but will get better if you can stop getting the leaves wet (water the soil instead of the leaves).

It does not necessarily kill the plant so, you could remove the worst of the leaves to improve the look but be careful to cut the leaf at the petiole that connects the leaf to the stem (do NOT cut the stem because that is where the flower buds for Spring 2017 reside). Dispose of plant material in the trash, not in a compost pile.

Here is more info:

http://www.aces.edu/pubs/docs/A/ANR-1212/ANR-1212.pdf

Other things you can do to help: pick up plant debris under the shrub; dispose of plant debris, infected leaves and infected/spent blooms in the trash (not in a compost pile); use drip irrigation if po$$ible; maintain some separation between the bush and other bushes to improve air circulation; replace the mulch with new mulch in cases of a large infestation. And sometimes, you can use fungicides.

You can use recommended fungicides in that link but, understand & think about these things first: (a) the leaves will soon be drying out so the fungicides will not do much for them this late in the growing season (b) these fungicides are not cheap (c) they do not cure but rather control the fungal infestation. If you want to use them, I would suggest applying some of the previously mentioned suggestions now and starting a fungicide program next year instead. Read the recommendations on the link.