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 Dave Shetlar noted that southern Ohio landscapers, nursery, and Christmas tree plantation managers should start monitoring for spruce spider mites (Oligonychus ununguis). The mite spends the summer and winter months in the egg stage. As temperatures cool in the fall, or warm in the spring, the eggs hatch making this a "cool-season" mite. Indicators that overwintered eggs are about to hatch include a GDD of 162, and the full bloom of 'Bradford' callery pears. Both of these predictors should be met this week with the predicted warm temperatures in that part of the state.
Hosts include spruce, arborvitae, juniper, hemlock, pine, Douglas-fir, true firs, and sometimes other conifers. The mites feed by rupturing individual cells of the host's foliage, producing characteristic tiny yellow spots, or "stippling." As the stippling coalesces, foliage becomes bleached and eventually bronze-colored. Inner foliage is generally affected first.
A "beating tray" is the most effective tool for discovering and assessing spruce spider mite populations. This tool can be a purchased piece of equipment, or simply a stick and an 8.5" x 11" tablet of white paper. Hold the white target beneath the conifer foliage and strike the foliage several times with a stick or rod causing the mites to drop onto the white target. Next, tilt and lightly tap the collection paper or tray to allow plant debris to fall off.
Look closely for small, slow-moving dots, not much bigger than the period at the end of this sentence. These are the spider mites. The faster moving dots are likely to be predaceous mites; the good guys that feed on the spider mites. A finger can be used to "mash and smear" the mites to further distinguish the good mites from the bad. Greenish-brown streaks are "pate de spider mite."
Effective management efforts include washing (syringing) mites from the foliage using a heavy stream of water, applications of soaps and oils, or applications of traditional miticides. Syringing will conserve predaceous mites, but may be difficult on large trees or large numbers of trees. Soaps and oils are also kind to predators, but oils will wash away the blue color on Colorado blue spruce. Certain miticides such as spiromesifen (e.g. Judo), hexythiazox (e.g. Hexygon, Savey), and bifenzate (e.g. Floramite), as well as a few others, have low impacts on beneficials.
For more information, see: 
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BYGL 
