Does anyone know what this is on my leaves?

[amber.leigh]

I've sprayed with Physan and it is still spreading amongst plants.

[estación seca]

Does it rub off? I wouldn't spray Physan without knowing what you are treating. It can harm plants like Dendrobiums.

[amber.leigh]

No, it doesn't rub off.

[Ray]

Boisduval scale?

[amber.leigh]

It doesn't peel off like scale. It's like it's affecting the tissue of the leaf.

[estación seca]

The leaf has been damaged, most likely by the scale Ray mentioned. It also could have been mealy bug damage. Did this happen recently, or did it come like this?

Physan doesn't kill arthropods. Inspect your plants closely for scale and mealybug insects. There are a lot of photos here on Orchid Board. Use the Search.

[sweta]

It looks like scale to me. I've had scale on some of my orchids which was hard to remove without damaging leaf tissue.

[estación seca]

If you spray scale with soapy water or 70% alcohol the adults die, and may be removed easily. Juveniles are likewise easy to remove. Residual scarring on the leaf can't be removed. That's why I don't think this patch represents scale insects, but might be old damage from scale.