Water the plant and soak the soil with a commercial fungicide.
Carefully follow the directions on the label.
Afterwards let the plant go completely dry.
If its not crown rot, the plant should be okay.
BTW, Saguaros make poor houseplants.
There are thousands of other cactus that fare much better indoors.
Ugggrizzly <ugggrizzly at aol.comnospam> wrote in message
news:20020209114219.11834.00000482 at mb-mq.aol.com...
> I while ago, I brought back from Arizona a couple of small potted of
> saguaro's. One seems to be OK but the other has a whitish fungus.
> I can do to get rid of the fungus?