Grasshoppers in Soybean

Crop Damage

Multiple species of grasshoppers feed on soybean including differential grasshopper (Melanoplus differentialis), migratory grasshopper (M. sanguinipes), redlegged grasshopper (M. femurrubrum), and twostriped grasshopper (M. bivittatus). Grasshoppers occur across the United States and into Canada. Grasshoppers have a wide host range, including many broadleaf weeds, grasses, vegetables, and field crops. Depending on the species and location, both nymphs and adults can pose a threat throughout the growing season. Also, they may be sporadic or persistent pests, with the potential for outbreaks. Nymphs feed on tender leaves, starting at the edges, creating irregular holes between the leaf veins. Extensive feeding can kill seedlings. Older nymphs and adults consume entire leaves, often leaving only the midrib. Adults injure the pods, even chewing through the pod tissue to feed directly on the seeds.

Pest Descriptions

Grasshopper species vary in appearance, but the nymphs of all species have wing pads rather than the fully developed wings observed on adults. Differential grasshopper adults are 1 1/4 inches long with yellow and black bodies. The upper part of the hind legs is yellow with black chevron ”V” shaped markings. The pronotum (the plate behind the head) has a light-yellow stripe on the top and a dark stripe on each side. Nymphs are pale yellow, green, or tan. Migratory grasshopper adults are 1 inch long and range in color from cream to gray. The wings are gray-brown with a row of dark spots. A distinct black band extends from behind the eye and across 2/3 of the pronotum. The lower part of the hind legs is blue or red. Nymphs have highly variable coloration. Redlegged grasshopper adults are 1 inch long, with dark brown bodies, and yellow on the underside of the abdomen. The lower part of the hind leg is red. A distinct cream band starts under the eye, makes an arc across the pronotum and travels downward, under the wing pads. Historically, outbreaks of redlegged grasshoppers have occurred in the Midwest. Twostriped grasshopper adults are 1 1/2 inches long and have bodies that range in color from olive green to tan. Two distinct horizontal cream-colored stripes run from the top of the head to the base of the forewings, converging to form a “V” shape. The upper part of the hind leg has a black band, and the lower part may be blue or gray. Nymphs transition from green to tan as they mature. Each side of the pronotum features a solid cream band with a partial black band above it. Similar to adults, the upper part of the hind legs typically displays a black stripe.

Scouting and Management

Grasshopper populations can build over time, especially during hot and dry conditions. Reduced tillage fields and undisturbed areas also allow populations to increase over time. Grasshoppers are known to be an “edge effect pest,” first feeding on grass or weedy areas on the edges of fields and then moving into soybeans. Grasshoppers feeding on alfalfa can easily move into a nearby soybean field when the alfalfa is cut. Effective scouting programs identify early infestations and effectively manage grasshoppers. Consult your local extension specialist for information on the grasshopper species and potential risk for infestations in your state. 

Thresholds are based on grasshopper populations or defoliation estimates. To determine populations, start scouting on the field edges. Visually estimate a square yard and systematically cover this area while counting the number of grasshoppers. Follow this procedure in 5 locations, noting the numbers of nymphs and adults present. If grasshoppers are located on the field edges, additional in-field scouting is necessary. Randomly select enough locations to represent the field—larger fields may need additional sites to represent the whole field. At each location, use the same procedure to count nymphs and adults. Economic thresholds for grasshopper populations differ for adults and nymphs (Table 1).

Table 1. Economic thresholds for grasshopper adults and nymphs.

Table modified from Scouting for and Managing Grasshoppers, North Dakota State University; and MacRae I, Potter B, Koch R., Grasshoppers in Minnesota Soybean, University of Minnesota Extension.

To estimate defoliation, begin scouting on the edges of the field. If grasshoppers are located, randomly select enough locations to accurately represent the entire field—larger fields may require additional sites. At each location, estimate defoliation for the whole plant and pod damage. States have a range of thresholds based on the species present, the timing of infestations, and conditions that favor outbreaks. The standard treatment threshold in soybeans is 30% defoliation in the vegetative stages and 20% in the reproductive stages. Some states consider multiple factors, such as defoliation and pod injury, for thresholds, which makes it important to consult local Extension specialists. Use the Crop Protection Network’s Insect Defoliation Tool to help you correctly assess the level of defoliation. Insecticides are more effective against nymphs than adults. Consider spot or border treatments if infestations are localized to field edges or small areas within the field. Carefully monitor treated areas, as adult grasshoppers are highly mobile and have many hosts; therefore, new grasshoppers may reinfest fields even after an insecticide application. Additionally, treatment may be needed in nearby locations where grasshopper populations are increasing. Late season applications should consider preharvest intervals.

Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.