Are you sure it's not fern spoor? Do you have any ferns close by?
Is the powdery stuff on the underside of the leaves?
I would get a magnifying glass or a loupe & check to see for spider mites.
Cheers Wendy
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t...
The leaves on many of my orchids (mostly catt family, dendrobiums, some
phals and paphs) are sticky to the touch. When I clean the leaves with
alcohol and cotton balls, a brownish powder comes off on some of the
leaves. At first I thought it was "dust" from moss or bark that had
become airborne when I squirted (I don't mist, I squirt the top of the
media) and stuck to leaves that had been treated with Neem oil or Safer
insecticide. (Previously, I had a problem with mites and mealy bugs.)

Many of the plants that have the dust are healthy, but a few are not. A
miltoniadium and some of the phals have ratty old leaves.

Now I'm bug free--visually bug free. And now that I'm doing a lot of
Ray's semi-hydroponics, I know that the brown dust isn't
splashback--many of my orchids are on humidity trays and in PrimeAgra,
which isn't dusty. However, even after I swab the plants' leaves with
alcohol, a week later, some plants' leaves are sticky again. So, do I
have another infestation of a new, smaller mite? Something else? Any
ideas of how I can get rid of it? Washing and swabbing everybody's
leaves every week is getting to be a drag.

BTW, I have had very good luck with PrimeAgra. It's a great cure for
those over-watered phals. Also, I started some Rodriguezia Secunda
babies in it, and they are taking off like a shot. The mother plant,
which is in bark/mass in a basket, has been mallingering since I got
her.)

Thanks for any help you can provide.