Spruce spider mite is active during the spring, along with other conifer spidermites, including pine mite, arborvitae mite, and juniper mite. Most of the available miticides are most effective against the active stages of mites and are not very effective against eggs.
The foliage of infested trees will be bronze in appearance due to tiny spots, stipples, of brown, damaged groups of cells surrounded by green, unattacked cells. Spider mites are sucking pests (related to spiders) that remove the contents of cells, causing them to initially be white; but these cells then die and turn brown. Heavily attacked trees frequently lose branches, and even entire trees can be killed. These mites spend the summer in the egg stage, which is relatively difficult to control. They hatch in the fall to feed for a relatively short time until winter. They spend the winter as eggs, hatching again in the early spring to feed.
Before miticide application is made, it is important to determine that active mite stages are present and that the population is sufficiently large enough to warrant control. It is common with spruce spider mite for an infestation to suddenly disappear, probably due to predation, weather changes, or other factors. Sometimes, the mite infestation does not return for decades.
Scout the mites by holding a piece of white paper under a branch and striking it sharply. This will cause many of the mites on the foliage to be knocked off onto the paper, where they can more easily be seen. They will appear as greenish to grayish specks that will be revealed with magnification to have six (larvae) or eight (nymphs, adults) legs. They will tend to move slowly and will streak green if smashed. It is common to also have faster-moving red mites that will streak red when crushed. These are predatory mites that are likely to provide biological control of the pest mites, if numerous.
Control spruce spider mites and other coniferous-feeding mites at this time with sprays of acequinocyl (Shuttle), bifenthrin (Onyx, Talstar), cyfluthrin (Tempo), insecticidal soap, or summer spray oil. With insecticidal soap and summer spray oil, repeat the application 1 week later. The other miticides should provide control with only one application. These mites are likely to remain active and susceptible to control until early May in southern Illinois, mid May in central Illinois, and late May in northern Illinois. A continued cool spring is likely to extend the season of activity, allowing more damage to occur if not controlled.