I have had success in growing african violets in small pots on the kitchen sink window ledge, but some of them kept getting white fuzzy spots on the leaves a few years ago. It does not seem to harm their ability to thrive, (that much). But I am worried they will infect my orchids etc.. Can you tell me what this stuff is, and how it can be treated so that it will go away ?
White spots on the surface of the leaves are most likely the early stages of Powdery Mildew, a fungal infection. If it is small fuzzy cotton-like bumps primarily at the base of the leaves, it could also be that your violet is infested with mealy bugs. In all cases, you should move these plants away from your other houseplants to keep the problem from spreading.
Powdery Mildew: Eventually the spots spread so that very pale powdery fungus grows evenly over the upper leaf surface of the leaves. It can be easily disturbed by blowing on it. It will also cover the flowers in the pale powder. Remove damaged parts. Space the plants out to increase air circulation and move them to a less humid location. You can then employ a powdered sulphur-based fungicide according to the package directions.
Mealy Bugs: Pick them bugs off by hand or wiping them away with a cotton swab dipped in alcohol, followed by a rinse with lukewarm water.
You may like to visit the site of the Toronto African Violet Society for more information about growing these lovely plants. And, our Gardening Guide to Growing Gesneriads provides guidance about the African Violets and related plants.