Spider Mites on New Dendrobium nobile
 

So, I accidentally brought home a “Typhoid Mary” about 4 days ago. It’s a small caned NOID Dendrobium noblie type. Today I noticed some sooty mildew and then a lot of stippling on the undersides of the leaves. From there, I was able to locate some mites. It was sitting next to a Phalaenopsis and a Dendrobium phalaenopsis type. How prone are these species to spider mites? I can’t find any on them yet.

I thoroughly sprayed down the Dendrobium nobile with an organic insecticidal soap that was advertised as being effective against mites. It’s currently in the peat perlite mix I purchased it in and just coming into bloom. I was going to let it flower first, but with the mite situation should I just repot now? I’m hoping the spray doesn’t destroy the buds, but there was no avoiding them.

I would not repot now. You might lose the flowers. Repotting is not going to help control the mites.

All those plants are susceptible to spider mites. You can treat them effectively by spraying all the plant surfaces with the insecticidal soap every 4-6 days for 3-4 treatments. The soap should not harm the buds if you mix it according to directions.

You will always need to be on the lookout for mites; they often return, and they are established in the landscape in many parts of the West.

Good to know. I’m going to watch the other two carefully and try to figure out where I can move them if I do end up needing to treat. The Dendrobium nobile has been relocated outside (hopefully it can take the temperature) and I’ll hold off on repotting.
No live mites found this morning and I’ll retreat in 4 days. So far none of our outdoor orchids have had mite issues, but I do know they’re around. These look to be two-spotted spider mites. My suspicion based on level of damage to the leaves is that it had a heavy infestation, was treated, I bought it, and am now dealing with the survivors; there were very few mites on the plant (I could only find ~6 when I went over it with a magnifying glass yesterday trying to figure out what I was dealing with).

The Den nobile can take low night temperatures above freezing, but the other two can't. Spraying with soap kills all the adults, but not eggs. That's why you need to spray a few times, at time intervals smaller than the generation length, which varies inversely with ambient temperature.