Martin wrote:
[tree with specs]

Depending on the species, a good wash under the shower may help.

I've had good luck with various insecticidal soaps at getting
rid of mites. You need to follow a term of treatment, to get
the unhatched eggs as well as the adults. Carefully read the
directions on the package.

If you are getting repeated infestations of mites, you should
consider the possibility that something is stressing your tree.
Things to check: wrong temperature, wrong watering, too much or
too little wind, wrong soil, too much or too little or the wrong
kind of fertilizer, wrong amount of sun or shade.

For indoor plants, be sure it's not in front of air vents or
in an area that is too hot. And be sure you are watering it
the right amount.
Socks