Spotted Oncidium Leaves

Question

What causes black spots on oncidium leaves, especially Oncidium Sharry Baby? -Brenda and Bill Dorsey

Leaf of Oncidium Sharry Baby showing spotting. photo © 2006 Greg Allikas

Leaf of Oncidium Sharry Baby showing spotting- photo © 2006 Greg Allikas

Answer

While some oncidium types seem to be more genetically disposed to the black-leaf spotting, and Onc. Sharry Baby is definitely in this group, all of them may get it at one time or another. The experienced growers with whom I have spoken tend to think of it more as a cultural problem than anything. It seems to happen when the leaves are watered from above, especially with cold water, and the water bruises the tissue, leading to secondary bacterial or fungal infection which is the actual spotting. The solution, therefore, would be to keep water off the leaves. -Ned Nash