The spots on the foliage look like a fungal infection caused by getting the foliage wet, poor  air circulation  or poor drainage. They could also be from herbicide drift if Roundup was sprayed nearby. The good news is that fall is coming and the foliage will all fall from the shrub soon. Then you just need to do good fall cleanup and rake all fallen leaves so they won't reinfect the shrub. In the spring you should see fresh new growth. A new mulch of wood chips on top of the root zone will also help to seal in any disease spores that could splash up onto the plant after you clean up the fallen leaves. I think your Rose of Sharon will survive this problem and be looking good next summer. Keep growing, Marianne Binetti