I usually only grow phals but I just couldn't resist this oncidium
with it's cheery yellow flowers. It stopped flowering about 4 months
ago. I changed the potting medium but otherwise left it alone. After
about a month it started to grow a new leaf bulb (I don't know what to
call it). It looked great, nice and green with several leaves.
Yesterday when I went to check on the orchids I saw that all the new
growth had turned a mushy brownish yellow. I cut it off before I
thought of taking a photo.

What would cause this to happen? It had to have happened over a
period of less than 3 days since I check the orchids at least every
other day. The older leaves look fine - for now. The other plants
are also fine - for now.

Help!