African Violet diseases

I have four nice African Violet plants sitting together on a table. I noticed one of them has something on the ends of many of the top of the leaves that looks like light brown "dried mud". It doesn't wash off with water and the plant appears very healthy otherwise. It hasn't spread to any of the other plants either.
Anyone have any idea what it is and how to get rid of it?
Alan C.
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Which leaves? The bigger ones, whose stems are closer to the rim of the pot? Or newer leaves which are more obviously growing from the center of the plant?
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It's on the leaves between those close to the rim and some new ones in the center.
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Check out this page from one of the largest violet growers in the country: http://www.lyndonlyon.com/Hints.html
If you love these plants, do NOT visit this place unless you're capable of controlling your spending. Or, walk in with a fixed amount of cash and no credit card. Don't ask me how I know this. :-)
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Jimmy-Bob wrote:

Do African Violets get scale? If it's scale the things would be easily scraped off with a finger nail or knife point. If it's scale, move the affected one away from the others and keep a close watch on the other ones for a while. I've never seen scale on an AV but I'm trying to make sense of your description. Any of these on the underside of any leaves?
Steve
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