powdery mildew caused by golovinomyces asperifoliorum on leaves of prickly comfrey or symphytum asperum

affected asperifoliorum asperum comfrey disease diseased foliage fungal fungi garden general golovinomyces green infection leaf leaves mildew pathogen pathology phytopathology plant powdery prickly rough russian spot spots symphytum uplandicum view white