Spruce spider mite and its relatives such as pine mite and juniper mite, are susceptible to control by miticides at this time of year. Damaged spruce foliage will appear bronze in color from a distance. When inspecting it closely with a hand lens, you will see that the foliage is covered with tiny brown spots where the mites have fed. These brown spots, surrounded by the green color of the needles, gives the foliage the bronzed appearance. Pine needles damaged by pine mite and juniper foliage damaged by juniper mite may be light green or whitish rather than bronze. On close inspection, this will be caused by white spots where the mites have fed. Foliage attacked by any of these three mites may be brown. These mites can kill the plants if damage is severe.
Scout for the mites by holding a piece of white paper below a branch and then striking the branch sharply. This will knock many of the mites off the foliage onto the paper, where they can be easily seen. Spruce spider mite and its relatives are tiny, relatively slow-moving, and greenish to gray, with eight legs. When smashed, they streak green across the paper. There may also be some other mites that are red and much faster-moving than the spider mites. They streak red when squashed. These red mites are likely to be predatory mites that are feeding on the spider mites. If they are common, treatment probably is not needed because they will control the spider mites for you.
Spider mites are most susceptible to control when they are actively feeding. Sprays of bifenthrin (Talstar), insecticidal soap, and summer spray oil should be effective at this time. Christmas tree growers and nurseries can also use dimethoate (Cygon). Repeat the spray one week later. Realize that spray oil removes the blue bloom from Colorado blue spruce and junipers, making them green. Depending on the weather, these spider mites lay over-summering eggs in late April in southern Illinois, mid-May in central Illinois, or late May in northern Illinois. After these times, these miticides will not be effective on these mites until fall when the eggs hatch.