I have black spots accompanied by a yellowing of the leaves on my Onc. Sharry Baby (see pictures below). I have read that it is a common occurrence, but wasn't sure if there was a treatment method or if this is something to worry about at all. I do plan on repotting after the next two spikes finish blooming.
Unless you grow in a greenhouse env I'm not sure anyone can grow these things without those stupid black spots and ugly leaf endings. At least I haven't and yet mine grow and bloom just fine.
Is that older foliage? How does new foliage look? If the new foliage looks good, this probably isn't something to worry about. Seems the old foliage is the most susceptible - at least on mine.
Those are cold spots caused by droplets of water that reacted to sunlight. I don't wet the leaves when watering. Sometimes those black cold spots get infested by fungi so watch out if there is yellowish circles around the black areas then you will have to cut it off.
The leaves of this kind of plant is thin and sensitive to light. They may easily burn in direct sun or even indoors on window sills they still react to the sun. And yet they need bight shaded sun.
I have seen plants in situ or outdoors in nature and they really get ugly leaves. If you found a plant like this with perfect leaves then it means it was well taken cared for and well loved by the owner.
I have to disagree on that, though. My plants don't get wet leaves either, mine are watered and fertilized and the new growths are beautiful. But the older leaves will get these spots and it doesn't seem to matter what I do.
It can be caused by fungal infections that are, while not harmless, are nonetheless benign for the most part. These spots can also be caused by fertilizer buildup in the potting mix. Or by hard water. Too much calcium carbonate, manganese, iron, or phosphates can cause this leaf tip spotting. But most folks get this type spotting. Most good nurseries don't get this because they have very good water, feed sparingly, and have lots of air flow.