Mold on base of indoor plant

[Rajah]

I have some mold growing on the base of an indoor plant I have. Any suggestions on how to kill the mold without killing the plant?

The plant is one of those that grows out of a piece of lava rock that you just keep in an inch or so of water to keep alive. It gets its nutrients from the rock. Will putting the rock entirely in water for a few days kill the mold without killing the plant?

 

[UrsulasShadow]

The mold is probably from the constantly wet conditions. I'd spray with a fungicide.