Despite the torrential downpours in the spring, many areas of the state are becoming very dry, with little rainfall in the forecast but with very hot temperatures. Although we have not heard of outbreaks in Ohio yet, there is a risk of mite populations beginning to increase in soybeans given the weather conditions. Whether mites do become widespread problems is unknown; however, growers in dry areas might want to begin checking their fields for possible mite infestations, especially around the field edges. We would not expect whole field infestations; growers should nevertheless also check areas within their fields. Additionally, any fields with fungicide applications (which can kill fungal pathogens that keep spider mite populations in check) should be prioritized for scouting. Early symptoms of two spotted spider mite infestations are yellow stippling of soybean leaves. Two spotted spider mites are small (smaller than soybean aphids), brown and black and can be seen with a hand lens on the underside of the leaf. If a leaf is removed and shaken above a white piece of paper, the mites will fall, crawl around and make it easier to see. See our fact sheet http://ohioline.osu.edu/ent-fact/pdf/0024.pdf for more information on two spotted spider mites in soybeans.
If mites begin to build up in fields, growers have a few choices in materials to spray (see http://entomology.osu.edu/ag/images/Soybean_-_Mites.pdf) which will do an adequate job in control: chlorpyrifos (Lorsban and various other formulations), dimethoate, and bifenthrin (various formulations), and various mixes of different materials including Hero which is zeta-cypermethrin and bifenthrin (active against mites), and Cobalt which contains gamma-cyhalothrin and chlorpyrifos (active against mites). Growers seeing yellowing along field edges should check for mites with a hand lens and consider a field-edge treatment. If the problem exists throughout the field, an entire field spray should be considered. We would also recommend using materials that offer mite control rather than suppression alone.