Gray mold or mildew on streptocarpus leaves
I am growing about a dozen strep plants that I purchased about six months ago. For most of that time, I have noticed on most if not all plants a light gray color will appear on a leaf and spread across the upper surface. Assuming that this is a mold or mildew, I spray with diluted Physan 20 and the gray disappears for a while but can then re-appear. The leaf remains healthy and green despite this. Has anyone seen this and do you know how to prevent the re-occurrence?