Rhododendrons: Rhodo 'unique' struck by powery mildew

I have a very large (approx. 12' H, 10ft L; 2ft W) "Unique" rhodo. Unfortunately it gets hit by what I believe is powdery mildew every year. The leaves have pale blotches and are weak looking and many turn brown fall off by mid year. Some branches also die back. Spraying with sulphur and/or fungicide seems to help temporarily but I'm not sure I'm catching the problem at the right times of the year. Also, how much can you spray with something like sulphur and not harm the plant? I love this old rhodo -- it has incredible trunk structure and I'll love to give it some relief from the problem. Any help appreciated!

 

Sadly, Unique is one of the most susceptible cultivars to powdery mildew. Good drainage, good airflow around the plant, careful summer irrigation to avoid stress from drought and mulching to reduce frost damage to roots in winter are the measures you should take to protect this highly desirable rhodo!