What’s wrong with these Dendrobium leaves
 

I have three dendrobium plants exhibiting something I’ve never seen. Leaves are rough and white/gray. It doesn’t wipe off with alcohol on a cotton pad.

Note: I had to leave home suddenly for a family emergency and the south Florida humidity would have to be the source of water. I didn’t know I’d be gone nearly a month. Most plants didn’t suffer much, if at all. So, I’m hoping this is dehydration that can be remedied with time.

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That is almost certainly spider mite damage. They are active when it's hot and dry. They may be mostly gone if it's been rained on recently. I would spray all surfaces of the plant, surface of the medium and pot with isopropyl alcohol 70%, rubbing alcohol. Going forward, wetting the entire plant once a week limits their activity. You can't get rid of them because they are in the landscape around you everywhere, so you must be watchful.

Mite damage. I would spray with 2% solution of horticulture oil. The false spider mites are really hard to control.