Answer: According to the African Violet Society of America, powdery mildew can be treated with several fungicides; you might want to refer to their trouble shooting chart for the specifics:
Also, be sure to read and follow the label instructions carefully. Air circulation and good sanitation are also very important in an effort to control mildew.
Most of the plants we grow are hybrids. However, in the wild, the plants would not be subjected to the stresses of a greenhouse and would be in a more ideal environment.
In a closed terrarium, where it is still and very humid, they do not seem to suffer disproportionately from fungal infections as long as the plants are healthy from the beginning. In the wild, if they grow beneath larger plants, rain might not hit them on a routine basis. In my experience with these as houseplants, a certain amount of tepid water on the leaves does not harm them as long as they are not in direct sunlight and as long as there is good air circulation to dry them off quickly.
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