Spider mites love warm, dry conditions. Here, they aren't so much affected by humidity but they go away completely once it starts to rain regularly. I think either they drown or they are washed off the plants by the water.
Or if I remember to hose off the plants they like regularly. That's all it takes. They absolutely love my Brugmansias and will decimate them in preference to almost anything else in the garden. As long as I spray the plants with the hose every few days (if there's no rain) I have no problems with mites at all. I love the Brugs but their real value is as a sacrificial lamb to attract all the spider mites for miles around so I can drown/wash them into oblivion.
I used to fuss with soapy water and neem oil and alcohol and other stuff. No more. Hose the plants, done deal.
