I'm in South Florida (Zone 9-10) where we had more than useual night
rainfall several weeks ago; very little sunshine and less than a gentle
breeze for well over a 2-week period. All my Catts are under 50% shade
in a lath house along with Bc. Maikai and a few ferns... and about three
weeks ago I started noticing leaves dropping over night at a very fast
rate that I've never noticed in the six years the orchids have been
hanging. Most everything I grow is bare-root and in wooden cedar baskets
(and doing what they're supposed to be doing year-after-year) and I've
never had an insect problem to really speak of nor any other fungal
problem... and, though I've seen Black Rot before, I've never seen it
being so 'selective' where it's only attacking new growth. I apply the
proper material to help control the problem... and the rate at which the
fungus originally hit had dropped down to where it's somewhat acceptable
-- considering what could have happened if I had not noticed it as soon
as I did. I've been cutting away, deeply into the rhizome where needed,
and doing everything possible (even isolate) to help stop the spread and
I think I've reached control even though I had to discard approx 10% of
my pants, but my question is: why is it only attacking my bifoliates and
not the unifoliate stock (both are hanging intermingled)?

Any help would be greatly appreciated.

BTW, I also grow Bc. Maikai in full west sun (except for July/Aug where
I drop them down a bit), and though they are somewhat sunburned at times
-- along with not even a trace of showing dark green leaves... they
flower like there's no tomorrow. They do darken up a bit over winter and
not the first sight of any fungus is ever noticed. I fert everything
weekly as well.

Thanks, and enjoy your growing.

John

Black rot fungus can infect the roots and leaves of orchids. This fungus shows itself on the orchid's leaves first, giving new foliage a rotted yellow or purple-brown appearance. Leaves later turn black. Black rot can spread to the roots in its later stages so infected orchids should be treated promptly by removing infected areas with a sterilized knife. Apply fungicide, and avoid overwatering while the orchid is recovering.

Fungus grows well in moist environments, so be careful not to overwater your orchids. Skip watering on cool, cloudy days or when it is raining. When growing orchids inside, use fans or open windows to keep the air in the room moving. Stuffy environments also encourage fungal growth. Treat fungus promptly when you discover it. If you are growing multiple orchids, you may want to move the infected orchid away from other plants so that the fungus will not spread while it is being treated.