Oncidium with damaged leaves
 

Hi everybody,

Would anyone be able to diagnose the damage on the leaves of this oncidium. The plant has two pseudobulbs. One with the leaves pretty much clean, but the other with extensive lesions. The lessons are round, pale and have a white center. Elsewhere there is some rust coloured damage of irregular shape. Please see the attached photos.

I have never seen anything like this and wonder if this could be sun/cold damage, fungal infection or pest. I should add that the surface of the damaged leaves is a little slimy.

Many thanks for your help!

How cold? It looks like fungus growing at the center of a zone of infection.

Quite cold. Perhaps around the freezing point. A bit higher.

That could be responsible for the initial damage. The white mold might be growing on already-dead tissue. Most white mold on plants grows only on dead tissue during periods of cold temperatures and high humidity. Imagine lettuce or carrots you forgot in the back of the refrigerator crisper drawer.