Looks almost identical to my catt a few weeks back! All new pbulbs were brown or turning brown, would dry up, turn black and fall off. It was black rot. I cut off all brown parts -in some cases i had to dig out the rhizomes as the rot had advanced quite far. I sealed all cuts with cinnamon (supposed to have anti fungal properties). Then i sprayed with an anti fungal product called Aliette (there are different ones on the market. I live in Europe) and just basically kept them out of too much sun. I resprayed it another time a week later just to be sure. So far, no more pbulbs have turned brown although the plant isnt doing much else. Will have to see if it survives the winter -i hope so!

If you have the same problem, you have to act FAST. Black rot spreads quickly and easily (via water) - isolate the sick plant from the rest of your collection. Apparently, catts are particularly susceptible to black rot (sigh).

I don't know, it looks like cold damage to me. Why are you growing Catts in a cool greenhouse in zone 4? Not a good idea.

Jane

Birkie, can you please describe exactly how you are growing it? Temps, light, etc...

Can you also tell us, do the spots sink in when you touch them?

I agree with the comments on black rot. Cut of all the affected parts back to healthy tissue. You may end up with more than one plant! I don't repot after the surgery but leave the plant on a bench and let it dry out before repotting in a week or more. Your chemicals don't work on the rot inside the plant, it has to be physically removed.

Nick

I too think black rot. All the affected plants are divisions of one overgrown pot, potted up a couple of weeks ago. I will try surgery on one or two that have the fewest symptoms and will toss the rest. A note to jane__ny, however. I have grown catts in my greenhouse (mim. 50*) for 15 years and have several dozen of various kinds. They are quite happy and bloom well, so I'm sure that is not the problem.

Well, seeing you live in zone 4 and are growing in a cool greenhouse, I frankly did not understand that.

I've frozen a few plants in my day and they looked similar to yours. Black rot usually spreads from the base of the pbulb upward.

Jane

Just my two cents on temps - I've always overwintered my catts in very cool conditions and kept them out in the balcony basically until first frosts. My plants are very hardy, though, and pretty much used to this regimen. I also keep them almost dry when it's cool/cold.They bloom profusely after i bring them inside in early November and once again at some point in the summer.
But, what's good for an older established plant is probably not applicable for freshly repotted ones, where cool+little sunlight (it's almost winter) spells danger...

Growing cats cool and dry is okay, but growing them cool and wet is disaster. The key words in parodise's two cents is "I also keep them almost dry when it's cool/cold." Think back. Could your plants have gotten wet when the temperature dipped?