Wilsonara dark spot on new growth spreading. Rot?

[Student Hobbyist]

Hello, I have had this Wilsonara for a couple months now and up to this point it has given me no problems. It is potted in sphagnum moss in a plastic pot with ventilation slits on the side.

It came to me with very little roots, but has adapted nicely to my plant room (or so I thought) and has even been working on a new pseudobulb.

Over the past week however, I have noticed a dark spot on one of the leaves associated with the new growth. I am aware that some orchids can have a dark pigmentation in their leaves that is completely normal but this has me worried. It has continuously spread up and down the blade of the leaf from where it started.

*please see attached photos*

I am worried that if it is a disease or fungal problem it will spread to the rest of the plant and kill it.

Can anyone advise me on what this spot is and if its is threatening to the health of my plant? If it is should I simply cut the affected leaf, or should I be more drastic and cut away the entire new growth so it doesn't spread to the rest of the orchid?

Thanks for any advise.

[Roberta]

I would just cut away the spot - a single-use single edge razor blade works well for this sort of "surgery". After you get the part with the spot, you can dust the cut edge with cinnamon to facilitate drying, it also acts as a mild fungicide (and even smells good) Then just keep an eye on the plant. You won't need more drastic surgery unless it shows up again and shows signs of spreading. In general, I prefer to do the least damage that I can, and then just observe. Most of the time cleaning up an area solves the problem - if your observation shows otherwise, you can consider further action, but you're likely to do more harm than good trying to get too far ahead of what's going on.

[claypot]

Just cut the leaf off below the mark and the plant will be fine.

[estación seca]

See the wrinkle further toward the tip of the leaf? That means it got too dry. Oncidium hybrids are very thirsty. Getting too dry is also able to cause leaf spots like the one you show.

[SouthPark]

The observation from E.S. about the wrinkled leaf is a good one. Also - if you do encounter fungal issues ----- then one possible method of treatment is to use one of those fine mist sprayers that hair dressers might use, and load it up with suitable concentration copper solution (for plants/orchids). And mist the leaves. And have gentle air movement in the growing area.