During the last two weeks we have received reports of increasing numbers of small white insects present on soybean. The insects in question are whiteflies (Figure 1). Although large populations of whiteflies may be present on soybean in South Dakota, the consensus is that they will not cause noticeable yield loss. This is likely due to the fact that the species of whiteflies that we see in the northern U.S. are often the greenhouse whitefly. In the Southern U.S., the sweet-potato whitefly has an economic threshold and is known to cause yield loss in soybean.
Whiteflies are approximately 1/16 of an inch long. Their head and thorax are cream colored, and their four wings are white in color. When feeding, the wings are held in a tent-like position over the body. Whitefly adults are easily disturbed during scouting and will fly up from infested leaves.
Whiteflies feed on soybean and other plants using piercing-sucking mouthparts. Both the nymphs and adults feed on plants. Feeding injury will resemble two-spotted spider mite with yellow speckling occurring on infested leaves. Heavy feeding injury will cause leaves to become dry. In South Dakota, it is unlikely that whiteflies will cause yield losses unless very large populations are present in the soybean fields. For this reason, we don’t recommend applying foliar insecticides for this pest. However, if foliar insecticides are applied for other insect pests or two-spotted spider mites it is likely that the whitefly populations will also be reduced.