I have a huge mophead hydrangea. I'm new to caring for them, but I have black spots forming on the top of the leaves. Also the new flowers are turning brown and dry before they've even reached their full growth. When I moved into this house about a month ago, I deadheaded all of the dried up flower heads and lightly pruned the dead wood. Does anyone know what these spots are? They're pretty big. I haven't seen any evidence of any bugs under the leaves, but I saw a small white film that almost resembles cotton on one of the stems. I also saw a little of that "cotton" looking stuff on a stem of a coneflower, which is on the other side of my property. Should I spray everthing with insecticidal soap, or what should I use?

Thanks,

Michelle