The picture of a dendrobium below is as close as I can get to the leaves but it still doesn’t show the tiny, slightly yellowish/clearish pests on the leaves. With a 30X lope I can see the critters but just barely – they must be the size of a straight pin point and I believe the white stippling is an aftermath of the pest activity and it is pretty bad on two dends. The stippling is on both the top and bottom of the leaf but much worse on the bottom. I tried using a q-tip dipped in alcohol to get rid of some of the stippling but no deal. I also found several dry black splotches within the white stippling and one (fresh?) super tiny shiny black bubble that reminded me of a tiny drop of old used motor oil – absolutely black. No webbing but from some internet searching I’m suspecting that these tiny critters are mites, possibly flat mites.
I have all my orchids in a lath house and even with fans and misting it gets pretty warm in there and I can only maintain about a 40 percent humidity. Never had to deal with this problem before and have read many sites that suggest miticides, oils, and/or insecticidal soaps. I’m leaning toward the insecticidal soap.
Before starting to spray, or to chop, or to throw away I would like suggestions as to what to do from somebody who had dealt with these critters before.
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I wish you luck getting rid of them. Someone will likely recommend a good chemical to get rid of the mites and that is probably your best bet. I took the difficult path and sprayed everything infected with spidermite with olive oil cooking spray, let it sit overnight, then scrubbed it all off with soapy water. It was a real pain but I got rid of them. :|
Bayer 3 in 1 for roses and Bayer w neem oil are both systemic that kill mites. Definitely separate from the other plants until its contained! Good luck I just finished battling fungus in my collection. Also the neem oil is a bug barrier I use on all my big plants roses gardenia etc...1x every 2 months in the thick of grasshopper season! Kills them once they begin to nibble. I trimmed my crepe myrtles and dead grasshoppers fell on me!!!
Many insecticides don't affect them, make sure and look for one that says it does. However one treatment won't be enough, they need repeated treatments to get rid of them.
I've got rid of them on some plants by regular washing with just rain water. (I'm talking at least a couple of times a week). They don't like damp conditions so stay away. However they re-occured when I stopped washing regularly over the winter so I don't think that really get's rid of them, just keeps them from doing damage.
You might also consider SucraShield, as a non-toxic alternative. Unlike any other insecticide/miticide, it kills all stages of the critter's development from eggs to adult, not just adults.
In chemicals, NEVER use insecticides against mites save if they are specifically labelled for. Some insecticides actually make them grow their population faster.
I've got to put in a plug for Sucrashield here. It has gotten rid of stubborn mite populations for me more than once. I found I had to use it more often than the recommended intervals to vanquish mites-- I sprayed every time I watered until the mites were gone, and I use it periodically now to keep them gone.