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Grasshoppers on soybean

Identification of Grasshoppers

Common species include the following:

  • Redlegged (Melanoplus femurrubrum)
  • Differential (M. differentialis)
  • Migratory (M. sanguinipes)
  • Two-striped (M. bivittatus) and 
  • Clearwinged (Camnula pellucida) grasshoppers
redlegged grasshopper nymph on the end of a plant leaf.
Figure 1a. Redlegged grasshopper (top).
adult differential grasshopper on a cut piece of a tree.
Fibure 1b. Differential grasshopper adult (bottom). Photo: David Riley, University of Georgia, Bugwood.org

Eggs

Eggs are formed into a pod and laid in soil. Grasshoppers overwinter as eggs in the soil.

Nymphs

Nymphs resemble adults, but lack fully developed wings.

In early to late spring, depending on the species, eggs hatch and nymphs emerge. Grasshopper nymphs undergo five molts.

Adults 

  • Between 3/4 to 2 inches long.
  • Color varies between brown to gray to green.
  • All have enlarged hind legs for jumping.

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.

For a detailed description of each species, please see the Extension publication, Minnesota Grasshopper Management.

Summer lifecycle of major cropland grasshoppers

Grasshopper species Nymph stage Adult stage
Twostriped (Melanoplus bivittatus) May through early July Early June through end of season
Migratory (M. sanguinipes) Mid May through mid August Late July through end of season
Clearwinged (Camnula pellucida) Mid May through mid August Late June through end of season
Redlegged (M. femurrubrum) Late May through late August Late June through mid August
Differential (M. differentialis) Mid June through mid August Mid August through end of season

Impacts

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

soybean pod damaged/eaten by a grasshopper
Figure 2. Grasshopper damage on soybean pod. Photo: Kelly Estes, Illinois Natural History Survey

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 one 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 nine.

As plants get larger, visually inspect plants for defoliation. To estimate defoliation, examine a minimum of 10 plants.

To estimate percent defoliation:

From each 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. 
  • 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.

defoliation of plant leaves by Bean leaf beetle, by Japanese beetle, by Green cloverworm.
Figure 3. Percent defoliation of soybean leaves. Photo: Robert Koch, University of Minnesota

Thresholds

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 percent. 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.

Treatment

Labeled rates of insecticides can be used to manage this pest. Follow directions on the product label.

Robert Koch, Extension entomologist and Suzanne Wold-Burkness, research assistant 

 

Reviewed in 2015

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