Grass Bug Damage Rises During Drought

By Scout Nelson

Black grass bugs are becoming a growing concern for forage producers across South Dakota as drought conditions continue affecting many parts of the state. These insects are common early-season pests that feed on grasses during spring growth, causing reduced forage quality and plant stress.

Patrick Wagner, SDSU Extension Entomology Field Specialist along with Philip Rozeboom, Brad McManus, and Adam Varenhorst, highlighted that dry weather conditions make the problem worse because stressed grasses have a harder time recovering from insect feeding damage. The latest U.S. Drought Monitor shows large areas of South Dakota facing abnormally dry, moderate, severe, and extreme drought conditions. Because of this, monitoring black grass bug activity is especially important this year.

Black grass bugs are small insects that are usually black or black with tan-colored edges. They are about one-quarter inch long and have large eyes on the sides of their heads. The insects produce one generation each year. They survive the winter as eggs and hatch in spring when grasses begin growing again. Young insects feed on tender grass before maturing into adults within several weeks.

Damage from black grass bugs appears as small light-colored spots on leaves, called stippling. Heavy feeding can lead to stunted growth and lower forage production. Wheatgrasses, including crested and intermediate wheatgrass, are especially vulnerable to infestations. Pastures and roadside areas with large wheatgrass populations are often most affected. In severe cases, the insects may move into nearby wheat fields, although damage usually remains near field edges.

Experts recommend regular scouting of pastures and fields to identify damage early. Producers should look for discoloration, stippling injury, and the insects themselves. Sweep nets are useful because black grass bugs often drop to the ground when disturbed.

Several management practices can help reduce populations. Intensive spring grazing can lower feeding injury and reduce survival of egg-laying females. Fall grazing, mowing, or controlled burning can also remove eggs found in grass stems. In areas with severe infestations, insecticides such as Malathion may help control populations during spring emergence. Experts note that yearly treatment is usually unnecessary because populations often take several years to increase significantly.

Photo Credit: gettyimages-v_zaitsev