Problem
How do I treat powdery mildew on my red valerian 'Albus'?
Centranthus ruber 'Albus'
Powdery mildew on a red valerian 'Albus' usually has one of three causes — watering, light or a pest. Walk through them in order before reaching for a treatment.
Most likely causes
Detailed cause-by-cause guide is being prepared. In the meantime: check watering rhythm, sunlight match, and any visible pests on the underside of leaves.