Tiny red dots on Dendrobium
 

Hello there!

My wife's Dendrobium has tiny red spots like dust on the underside of the leaves. Under a microscope they are about 50um long elongated ovals, suspiciously like eggs (see attached photo). However, they've been around for sometime and no bugs have ever emerged. Any idea what these might be?

Thanks,
Andy

Welcome to the Orchid Board!

I don't know what that is. Another possibility is a fungal fruiting body. Do the dots rub off with hand pressure? Rinse off with water? Does the plant seem unhealthy? What are your growing conditions?

Gives me flashbacks to a grueling multi-year campaign against flat mites on my Portulacaria afra and Elephant Ears, but if it were an active infestation you'd certainly have noticed adults under the microscope.

Are they in clusters? Is the plant kept indoors? How long has it been since you noticed them? In cooler weather mite eggs can take 4 weeks to hatch, and extended cold periods (~50ºF/10ºC) can render them nonviable.

Fungal spores?
 

I seem to be unable to reply in full as my posting gets blocked for "forbidden words", which I find baffling. Is there a list of the forbidden words somewhere? Anyway, it seems clear that the 'red dots' are fungal spores and, given that there's no apparent damage, are (to quote Ford Prefect) mostly harmless.
Many thanks,
Andy