Summer means spider mite season. Although mite populations are low now, they will increase during hot and dry weather. The following is a good article on spider mite control from Rutgers University.
Controlling spider mites and protecting spider mite predators
The use of Horticultural Oil is still an excellent choice as a miticide when adequate coverage can be achieved and infestations are moderate. When the time and effort is taken to apply a thorough oil spray application against a population of mites, the results are usually satisfactory. Oil suppresses three stages of the mite life cycle (egg, immature, and adult). It also has less impact against predatory mites (as well as other predators) than do most traditional miticides.
When using miticides, the objective is to maximize your control of the pest mites and eliminate friendly fire to the predatory mites. Fortunately, several recently developed miticides have this unique ability. Examples of these new materials include Hexygon and Tetrasan. These materials are now registered for use on exterior ornamentals and they control the eggs and immatures of only spider mites (neither eriophyid nor predatory mites are affected). Both are “mite growth regulators” and inhibit the formation of chitin, the building block of the outer exoskeleton. Floramite is another miticide impacting only spider mite pests. It controls adult mites and provides egg suppression against two-spotted spider mites. Furthermore, all of these miticides have at least a three-week residual.
Hexygon and Tetrasan do have potential disadvantages since they do not control adult spider mites. Therefore, a large infestation of spider mites treated with these materials may continue to feed as adults and cause damage for two weeks or more before a majority of the population dies off. Observations using Hexygon indicate that treated adult female mites become sterile and any laid eggs do not hatch. Horticultural Oils are compatible with Hexygon and Tetrasan can be mixed together to provide reinforcements to suppress the adults.
Reprinted from "Landscape IPM Pest Notes" by Steven K. Rettke, Ornamental IPM Program Associate in the May 28, 2009 edition of the Plant and Pest Advisory, Landscape, Nursery, and Turf Edition from Rutgers University.