If that plant has half a (plant) brain . .
it will have roots all into the lovely sponge, won't it?
Maybe try dunking it in a mild h2o2 solution? Hmm, wonder if it would affect the sponge as well as the mold? Maybe try putting some peroxide on a small spot on the sponge with an eye dropper and see what happens, first? Then if it kills off the mold but doesn't nix the sponge in the process, you're golden. Dunk it!
