Black stuff on underside of dendrobium leaves

[bulblehead]

Hi ! This dendrobium nobile just finished flowering and lost a bunch of leaves. Some of the ones that remained have this stuff in the bottom side. The spots are not on the keiki leaves (there are a lot of keikis). They look like a black dust on the underside but doesn't come off.

Does anyone know what it is? I sprayed some neem oil jut in case.

Some notes on the growing conditions, it has been super dry the past month or two I've had it (25-35%). Temperatures are 60-80 night vs day. It's in sphagnum moss and watered once a week (stays pretty mosit /wet). And it's by a large north-east windowsill.

[Nexogen]

There appear to be traces of spider mite attack. They have a special pleasure to attack the leaves of dendrobium and angreacum.

[estación seca]

Agreed, spider mite damage. A suggestion - don't take photos with the light behind the plant. We can't see anything in the first two photos.

[bulblehead]

thanks so much you guys! ok i will just proceed as usual and stay diligent watching out for pests.

spider mite (and other pests) season for me is usually the middle of the summer when it gets hot and humid :'D.

[estación seca]

Spider mites like it hot and dry. They aren't active much at humidity over 80%.They are recurrent winter scourges for people growing many kinds of plants indoors. You can prevent attacks by spraying your plants with plain water every week or two.