In my experience, fungicides are better for used preventing fungal outbreaks than they are for 'curing' them. You may want to remove affected leaves if possible. Acquiring good airflow through the canopy and reducing humidity will help reduce mildew.
That said, I wonder if anyone else knows of a way to treat affected leaf surfaces.
I remove and burn all affected foliage.
First application early morning when tree is dry.
Further applications depend on weather -
1) If it stays dry I reapply every 10 days
2) If it rains I treat it on the following morning that will be dry
It is a good idea to do an early Spring treatment just at the start of "pushing"