It looks like black rot. The plant is probably trying to fight off the infection thats why it was still able to put up some growth.
You will most likely need to cut off the new growth. If the infection makes it into the rhizome, it could spread to the entire plant.
Treat the whole plant with a fungicide. And repot into a new medium as a safety measure.

And be careful about getting water inside of new growth especially later in the day.

Thanks for the fast responses! I sliced off that new growth with a quickness--it was black and juicy inside the bottom portion but the base joint, where it was attached to the rhizome, was green. Out of curiosity I opened up the papery skin and there was a young black leaf inside.

I don't have time to re-pot tonight but I'll do it tomorrow after work. What causes the black rot, is it just getting water in new growth or is it overwatering? I'm thinking about re-potting in only bark and nixing the sphag.

Thanks again for the help :-)

If it's soggy, you've probably got black rot. If it's crunchy, I have a few that do that randomly. I don't know if I move them into an area where there's too much sun when they're growing or not. The crunchy you don't have to worry about; the soggy isn't good.

Stacy

Orchid rot is usually caused by different strains of fungi or bacteria. They seem to be present all the time in minute populations around orchids waiting for an opportunity to take over the plant.

Excess moisture combined with cold or stagnant air causes the fungus population to increase faster and overtake the plant.

New growths are highly susceptible because their current shape tends to trap more water and not allow it to evaporate. Their tender external bodies also allow easier pathogen incursion.

I personally do not use sphagnum moss for cattleya alliance orchids because the pot stays wet for too long. But other people have had good results with sphagnum as well.

Your plant looks robust and healthy, and it should be fine.

But, yes, the browning of those new shoots is rot. It happens, and as richard says, getting water into the new growth is one of the causes. Rain, or more often, splashy watering is enough.

All those tight little folds in the tender new growths can hold enough moisture to incubate a rot. That's why you see it in new growths most often. And it can spread into healthy tissue, too, as was mentioned above.

There's some notes on stopping rot in the culture notes at Al's Orchids. It's worth checking it out and reading them. His comments are about phals, but what he says should apply to catts as well: orchids have the capacity to create a barrier isolating healthy cells from the sick ones, and will do so if given any help at all. A contact fungicide/bactericide will help.

2 tsp of physan 20 per gallon of water is a good contact fungicide/bactericide. So is cinnamon.

I have used both, tho I tend to favor the cinnamon a little (I think it's because I can see it). But it really works very well on all kinds of problems.

BTW, I have read that *fast* rots are bacterial, and that fungal rots are slower. So from what you said about the overnight browning, it's probably a bacterial rot. If that's the case, a fungicide won't stop it. That's a good reason for using a fungicide/bactericide when you aren't sure what the cause of a rot is.

Just wanted to note that the night the new growth turned brown, DH left the window wide open (with catt right next to the window) and it has been cooling down at night, maybe in the mid to upper 50s. I don't know if that's too cool for a catt but it's a big temp swing considering the days are in the mid 90s (we keep the house around 82 but it might be a tad warmer by the window).

I'll definitely water more carefully from now on.

Yep, black rot. Serious stuff and it can kill a plant while you stand there and watch it.

I had a few catts with that. You really need to cut off the rotted part right into the good growth (sterile instrument) and treat it right away. I've had maybe 30% success using this technique and coating the cut end with 100% physan, repotting so the plant is in new media that dries out more quickly (I can't grow well in sphag either), and keeping the plant separated from others as much as possible.

If the rot isn't too far back into the plant and there are viable eyes and roots and the plant is otherwise healthy, it can sprout clean new growth from further back.

Good luck!

Sharon

That temperature swing is normal for Catts and is definitely NOT the cause here. Mine get that much swing every day.