Black spots / patches on underside of cattleya leaves

[mexicowpants]

Hi, bought a young cattleya "amatista" a few months back at an orchid show, during this time it hasn't seemed to grow very much at all, despite the same care as all my other catts, which are thriving.
Today I noticed that the underside of 2 of the leaves are more than half-covered in black patches / spots, which feel a little softer than the surrounding leaf tissue, and slightly sunken. Another couple of leaves are affected to a much lesser extent. I only just noticed it today because it's quite a small plant and only the underside of the leaves are affected.

My guess is a fungal or bacterial infection, although I'm unsure which. I've treated it with an alcohol rub so far, but was hoping one of the more knowledgeable people here could offer up some advice.

Thanks in advance!

[estación seca]

It might be a bifoliate species Cattleya or Guarianthe. Some have light purple flowers, hence "amethyst/ amatista." These tend to produce new growth only once per year.

The two leaves with black spots do look worrisome. The rest of the plant visible looks pretty good. I would cut it back well into good tissue. Sterilize the blade between cuts.

[silken]

I agree. I would cut that back to good tissue and treat the cut ends. Keep an eye on it and possibly segregate it for now.

[mexicowpants]

Already segregated, keeping a close eye on all the other plants it was close to (quite a few of them -- eek). Would Captan be good to treat the ends with after cutting back?

[estación seca]

We don't know for sure what it is. Cinnamon powder would probably suffice. ¿Te gusta canela?

[mexicowpants]

Originally Posted by estación seca

We don't know for sure what it is. Cinnamon powder would probably suffice. ¿Te gusta canela?

Me encanta

So cut back into good tissue, and give it a cinnamon rub-down, then? On it tomorrow. How far back into good tissue? The plant's not that big -- the large, badly affected leaf in the photo is around 10cm from base to tip.

[estación seca]

I would cut the bad leaves all the way back go where they join the pseudobulb. The plant appears to have lots more leaves, and it will recover faster from a curative total leafectomy than a brownspotectomy that leaves yet-invisible bad stuff.

While the cut is still wet, put some dry cinnamon powder on just the cut. It doesn't have to be anywhere but the cut.

[mexicowpants]

OK, surgery now done. First picture is of the wound site, treated with cinnamon. Second picture is a cross-section of the most badly affected leaf. Seems it wasn't as bad as it first appeared, only having affected the very outer part of the underside of the leaf, so I live in hope of a full recovery. Also treated the other, much smaller spots on other leaves with cinnamon. Plant now segregated and under observation.

On a brighter note, whilst treating the plant, I noticed that it has a new growth spike! Finally!

[silken]

Good luck and I hope it does well from here on.