Avoid using broad-spectrum insecticides that affect many species for general control of landscape and garden pests, because beneficial organisms will also be killed. This often results in outbreaks of spider mites or other secondary pests that were previously controlled by the naturally-occurring beneficials. All broad-spectrum insecticides, whether natural or synthetic, kill beneficial organisms as well as the spider mites, which can sometimes allow the spider mites to reappear and become an even worse problem because their natural controls are gone. If spider mites are a yearly problem in your area, management should begin in late winter or early spring with a spray treatment of dormant oil, on trees and shrubs that were infested the previous summer, to kill overwintering eggs. Removal of debris and a spring soil drench of insecticidal soap in areas where they were a particular problem last year can also help.
Sulfur can reduce populations of beneficial organisms.
Monitor for new infestations by holding a sheet of white paper under the foliage, then tapping the branch with a stick firmly enough to knock spider mites onto the paper. Beneficial mites which attack spider mites are available from mail order sources. In indoor settings they have been found fairly effective, but in outdoor conditions, the results have been highly variable. You might want to try some releases of your own and monitor the results. Often we see the best biological control result from protection of the naturally occurring beneficial organisms in your area, rather from commercial biological control products.