Updated Resource for Grasshopper Management

UMN Extension Educator (hans4022@umn.edu) - Integrated Pest Management, Ian MacRae - UMN Extension Entomologist, Bruce Potter - UMN Extension IPM Specialist, Robert Koch - UMN Extension Soybean Entomologist, and Fei Yang - UMN Extension Corn Entomologist

High grasshopper populations have been observed in several areas of Minnesota in 2023. If grasshoppers are a concern in your fields, a recently updated extension guide on grasshoppers in field crops will give in-depth guidance on grasshopper species, how to scout, and what thresholds and insecticides should be used for each crop.

Grasshoppers generally prefer areas with undisturbed soil to lay eggs such as in pastures, hay ground, field edges, road ditches, and sometimes cropland. The immatures (i.e., wingless nymphs) and adults feed on live grasses and forbs. The depletion of their food source from grasshopper feeding, roadside and hay land mowing, and small grain harvest can encourage movement to other areas, affecting neighboring crop borders.

Flying grasshoppers stop and land when they encounter a vertical object such as that represented by tall corn, so they are usually a border issue in corn unless infested very early or hatching within the field.

Differential grasshoppers are the species most likely to be found foraging deeper into MN corn late in the season. Pay close attention to corn near alfalfa or grasslands. Redlegged and twostriped grasshoppers will also oviposit in alfalfa and soybeans, sometimes well into the field.

Grasshoppers do well in warm, dry conditions when diseases that suppress their populations are less prevalent. Two or more consecutive warm, dry springs and drier than normal summers help explain the higher grasshopper populations farmers are seeing in areas of Minnesota. However, if grasshopper numbers and crop injury are below economic levels, it is not a good practice to treat grasshoppers to prevent egg laying.

Timely rains may still help suppress grasshopper populations, though wet conditions typically have a stronger effect on younger nymphs earlier the growing season by favoring the microsporidian Nosema, the fungi Beauveria and Entomophthora, and other pathogens. Growers should continue to keep an eye on their soybeans and other crops in August. The winged adults that are developing now are mobile and can move further into fields. While this may help disperse grasshopper densities, it also reduces the chances for controlling hopper problems on field borders. In general, grasshopper scouting entails determining the number of grasshoppers per square yard, though percent defoliation for soybeans can also be used as a treatment decision metric.

Source: umn.edu

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