The mites had invaded the field from a grassy border and caused significant leaf stippling in soybean edge rows. After scouting plants near the center of the field, mites were found but not in high numbers. Spider mites also have been reported on soybean in eastern Iowa, and some fields have been treated. Spider mites are small animals more closely related to chiggers, ticks, and spiders than to insects. Although many species of mites can injure plants, it is the two-spotted spider mite that attacks soybean and is the primary mite on corn in Iowa.
Most spider mites are greenish-white to yellow in color, although some can be orange or reddish.
The two-spotted spider mite is named for the two dark spots on the sides of the abdomen, which are digested food visible through the insect's translucent body. Three or four spots may be apparent and are most prominent on adult mites. Spider mite injury to soybean can resemble herbicide injury or a foliar disease, however, characteristic signs are tiny yellow spots, or stipples, on leaves. As the injury becomes more severe, leaves turn yellow, then brown or bronze, and finally die and drop off. Soybean plants injured by mites mature early, have increased shattering, produce smaller seeds, and may produce wrinkled seeds.