Possible disease on cattleyas

[ArronOB]

Hi. I have several Cattleya hybrid plants with a disease (I think) that I can’t identify.

The symptoms are:

Yellow, randomly shaped patches on the top surface of the leaf.

On the bottom surface of the leaf, and corresponding fairly exactly to where the yellow patches are, there are minute black spots. Like patches of dusty black spots.

The leaves feel normal and are not dried out or wrinkled.

The plant generally looks healthy if the yellow patches are overlooked.

Neither the black spots nor the yellow patches are discernible to the touch.

I looked at the black spots under magnification and they don’t reveal any particular characteristics (ie they don’t appear to be fruiting bodies), just tiny black marks.

On any affected plant, most of the older leaves have the symptoms.

I think about three plants are afflicted and it doesn’t seem to be spreading, which is surprising as I keep them close together with others and don’t limit splashing when watering or engage in other cultural practices that might limit disease spread.

The photos are of the same leaf, upper and lower surfaces. Ignore the fairly large chunks taken out by some passing insect.

I’m very worried about this one, so any advice appreciated.

Thanks
Arron