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. Early and severe mite injury left untreated can completely eliminate yields. More typical mite injury, occurring during late vegetative and early reproductive growth, will reduce soybean yields 40-60 percent.
Spider mites can cause yield reductions as long as green pods are present.
Soybean plants can recover from substantial amounts of mite injury after treatment, although less compensation is possible in later developmental stages. Before treating, check that living mites are present. Examine other areas of the field, especially downwind, to identify the extent of the infestation in healthy plants. Because they are small and stay on the undersides of leaves, spider mites can be difficult to see. One way to spot them is to tap leaves against a white piece of paper and look for moving yellow dots on the paper.