Grasshoppers in Minnesota soybean
Photo: Joseph Berger, Bugwood.org
Photo: David Riley, University of Georgia, Bugwood.org
Figure 1. Redlegged grasshopper(top) and differential grasshopper adult (bottom).
Common species include the following:
Redlegged (Melanoplus femurrubrum)
Differential (M. differentialis)
Migratory (M. sanguinipes)
Two-striped (M. bivittatus) and
Clearwinged (Camnula pellucida) grasshoppers
Adults (Figure 1)
- Between 3/4 – 2" long
- Color varies between brown to gray, to green
- All have enlarged hind legs for jumping
For a detailed description of each species, please see the Extension publication, Minnesota Grasshopper Management.
Eggs are formed into a pod and laid in soil.
- Nymphs resemble adults, but lack fully developed wings.
Reprinted with permission from "Minnesota Grasshopper Management: Corn and Soybeans." Ian MacRae, Bruce Potter, and Ken Ostlie.
Grasshoppers overwinter as eggs in the soil. In early to late spring, depending on the species, eggs hatch and nymphs emerge (see Table 1). Grasshopper nymphs undergo 5 molts. Adult grasshoppers mate, and females deposit eggs in the soil in late summer and early fall. Most species lay their eggs in undisturbed areas outside of fields, such as ditches, pasture, and CRP.
Both adults and nymphs feed on leaves, resulting in jagged holes. They can also feed on soybean pods, occasionally injuring the seed or clipping pods from plants (Figure 2).
Scouting and management
Because grasshopper populations often build in non-crop areas and later move into soybean, field edges are usually the first areas to show feeding injury, and where sampling efforts can initially be focused.
We recommend focusing early-season sampling efforts on insect counts, and as plants develop, switching to plant sampling to estimate percent defoliation.
Begin scouting for grasshoppers after plants emerge. Concentrate sampling on the field edge and count the number of adults and nymphs in a 1 square foot area. Repeat this for a total of 20 samples. To determine the number of grasshoppers/square yard (which thresholds are defined as), multiply your average number of grasshoppers/square foot by 9.
As plants get larger, visually inspect plants for defoliation. To estimate defoliation, examine a minimum of 10 plants.
To estimate percent defoliation:
- From each plant, select a leaf from the top, middle and bottom thirds of the plant.
- Use Figure 3 to estimate percent defoliation for each leaf and determine the average percent defoliation across the three leaves from each plant. Then average across the multiple plants (also see Visual guide for estimation of soybean defoliation).
- This average percent defoliation for the field's canopy can be compared to treatment thresholds.
Risk for infestation by grasshoppers is greater in years following long, warm autumns and warm, dry springs. Populations tend to build over multiple years, so high populations observed in one year could indicate higher risk the next year.
For defoliation-based thresholds, the following recommendations apply:
- For vegetative plants (before flowering), treat if grasshoppers are present and defoliation reaches 30 percent.
- For reproductive plants (flowering to pod fill stage), treat if grasshoppers are present and defoliation reaches 20 percent.
- Treat if grasshoppers or other pod feeding insects are present and pod injury reaches 10%. Treat aggressively if populations are large and pod clipping is occurring.
Management decisions can also be based on insect counts. To find out more about count-based thresholds, see the NPIPM fact sheet.
Labeled rates of insecticides can be used to manage this pest. Follow directions on the product label.