Brown Spot with Yellow Leaf on Dendrobium

[KristenJ]

Hi all,

I am hoping someone can advise me on how to properly treat my Dendrobium. Monday I noticed a small yellowing spot on the center of a leaf. I decided I would keep an eye on it and look it up. I believe it might be some kind of bacterial rot/spot but I am not sure and I do not want to treat incorrectly and make things worse.

I have attached two pictures. Monday there was a spot closer to the tip of the leaf. Yesterday there was the second spot closer to the center of the leaf. Both spots have darkened in color and the leaf has turned yellow. There is a green ring around the spot.

The cane is still the correct green color, all leaves are their normal green, roots that are sticking out of the medium and pot appear to be strong and healthy. I have never had problems with this orchid before. The leaf is on the cane that grew last year, but failed to bloom this year.

If anyone can help me figure out what has caused this and how I should best treat it, I would greatly appreciate it. Thanks!