Spotting and yellowing leaves on Den. aberrans - fungus?
 

https://imgur.com/a/CrG7idLI think it's fungus. What should I do? I have Physan 20 and 70% isopropyl, but that's about it.
Photo: Imgur: The magic of the Internet

There's always the possibility of those spotting to be fungus related. So - just in case - some backup treatments could be used --- such as thiomyl (sold sometimes are cleary's 3336), and maybe agri-fos.

Also look into possibilities of nutrient or chemistry element deficiencies - such as magnesium deficiency or even calcium deficiency.

To cut down on fungal issues, maintain some (even gentle) air-movement in the growing environment.

Have you been growing this orchid for a long time?

If leaves are yellowing - then immediately unpot the orchid and check the roots. If the roots are rotting, then clean them up, and repot into new media. And then use a watering method that avoids having the roots very wet for relatively long periods of time.

Are the growing temperatures satisfactory too?

Spotting sometimes can just naturally occur outdoors ---- such as if some insect comes along to feed on the plant, or some insect spikes it (maybe) in various spots for some reason. Not always an issue. It just means that outdoor plants (if growing outdoors) can sometimes have spots and marks etc, which doesn't necessarily mean health issues.

And relatively old leaves will come to an end --- eventually. But in your case - if most or all of the leaves are beginning to yellow, then check the roots right away.

http://www.orchidboard.com/community...1&d=1586460358

Yes. I would vote "fungus", as well.

The pattern is reminiscent of water spotting, which is likely the origin.