Yeah, some sort of rot. Best you can do is to cut the rhizome before the rot
spreds to the other pseudobulbs. Oncidiums can tolerate not having many back
bulbs. So if you can, cut the front 2-3 bulbs away from the infected portion
and toss the infected portion out. Heck, even if you end up with only one
healthy bulb its better than nothing. It may get set back by such heavy
surgery, but still its better than losing the plant. Oncidiums are
relatively tolerant as far as orchids go.

Make sure you repot in fresh medium. Medium should be chosen in proportion
to the size of the roots. Oncidiums have fine roots, so a fine bark should
be used. Use a new or clean pot so pathogens aren't transmitted from the old
pot. The size of the pot should just hold whatever good roots remain, even
if this makes the plant sort of top heavy. If it is top heavy after
repotting you can then slip the plant and its pot into a second larger
heavier pot (like a clay one) so it doesn't tip over. and so you don't
jostle it as it makes new roots and grows.

Whatever pseudobulbs you have left should be firmed up in the pot so the
plant doesn't move in the pot. You should be able to lift the pot by the
plant, it should be that firm in the medium and pot.

K Barrett

"west" wrote in message
...

It's sort of a tan brown. Starts at the base, gets about half way up
the bulb, and the bulb just falls off. New growth next to it goes next,
in the same manner. The brown area smells just like a rotten Bearded
Iris root. Rancid. Mushy. I know if I don't get control of it soon, I'll
lose the other five bulbs.

west