Black lesion on cattleya leaf

[Grim Tuesday]

About two weeks ago, I noticed this black lesion on the leaf of a previously thriving cattleya warcewski seedling. I sprayed it with a fungicide, separated it from my other plants, and transferred it into a less retentive media (it had previously been in "precision" orchiata and though the roots seemed happy, it was not drying out ever). Today I peeled the sheath of the pseudobulb and saw the lesion has not gotten to the rhizome. I don't think it has been growing since two weeks ago. So here are the questions:

1. What is this?
2. Should I cut off the majorly affected leaf? Or just leave it as is? You can see other leaves also have smaller black lesions on them. I am leaning towards doing nothing and letting the new growth develop.

[Louis_W]

I would lean towards doing nothing. The two questions i would ask myself are:

Is the black area spreading?
Are the new growths healthy?

I think its good that you are letting it dry a little more. You should be on the right path, just avoid any more dramatic changes and give it time.

[estación seca]

I would have done things differently.

Seedlings are very delicate. This species resents repotting at the wrong time even more so than other Catt species. I would not have repotted.

That black pattern is common with scale or spider mites inside the developing leaf. I don't know whether your plant has bugs. I would have sprayed it with 70% alcohol to kill hatched bugs, and kept a close eye on it.

Blackening of new Catt growths happens with inadequate watering. The plant looks wrinkled and dessicated to me.

Fungus is unlikely unless temperatures are quite high or low and humidity is high. Few homes have conditions promoting fungal attack, and spots in windowsill or light stand plants are rarely fungus.

I wouldn't use a fungicide unless I knew what fungus I were treating and I knew the organism were susceptible to that fungicide. Not all fungi are killed by all fungicides. Treating can produce fungicide-resistant strains. It also kills beneficial organisms that protect plants from other harmful organisms.

I think your problem is caused either by bugs inside the sheath, or underwatering.

[Grim Tuesday]

Thanks! Good to know what to do for the future. I am fairly certain this plant had more than enough water at the roots, so I think underwatering is doubtful. If anything, there was too much water and not enough air.

I had one other plant that had phalaenopsis mites (false spider mites), the kind that don't make webs and produced a stippled pattern (at least on a dendrobium leaf). Could that manifest as these black spots on the cattleya?

[estación seca]

I don't know the answer to that. I would get out a magnifying glass and examine the crevices.