Rust appearing spot on inner most leaf

[Freanne]

I had this plant for 3 months - the inner most leaf appears to have rust type potting but not on both sides. Thoughts on what is causing this?

 

[Jpari]

That looks like brown rot to me. Did you top water too late in the day for the water to dry in the crown? I would treat with a strong solution of Physan 20 immediately.

 

[Theodoreorchidking]

If this is not erwinia, then I would remove the most of that leaf as possible. I had this happen and I literally just ripped it out and put hydrogen peroxide, diluted, and then put cinnamon on it. If it is not to far down the leaf will continue to grow. If it is then I potentially might save the plant and just sprout a new growth. I essentially removed the inner most leaves on a Harrold koopowitz and it didn't do any harm and produced a new growth. Honestly to keep it on and chance it is not worth it. Maybe cut a little bit off and smell it. If it has a bad smell like erwinia, throw it away or pull it out from other plants. When it is in the inner most leaves it is practical a death sentence for a one growth plant. However it may be something simple

 

[SelectOrchids]

Fusarium with a kind of 'crust' on top of the lesion. Usually it starts from the rhizome and crown base.

In most cases it is hopeess. Eventually feeding and fungicides can control it for a while, but it is usually systemic. One typical point is that it attacks a side of the plant only usually.

It can restart new shoots, usually several tinier ones, that take ages to grow, but eventually the infection is, for a hobbyist, incurable.

Nothing to do with top watering, water in the crown etc... but usually the plant is infected since a few months or more.