Minnesota's High Grasshopper Populations and Their Impact on Crops

Minnesota, a major agricultural hub, is currently facing a challenge with rising grasshopper populations. Experts from UMN Extension, including Ian MacRae and Bruce Potter, have observed a considerable increase in these pests in 2023. They've offered a comprehensive guide to assist farmers with this menace.

Grasshoppers usually choose undisturbed soil areas like pastures, road ditches, or hay grounds to lay their eggs. Both their young and adults feed on live grasses. With their primary food sources depleting, grasshoppers often move to neighboring crop fields, especially to the borders of tall crops like corn. In fact, Differential grasshoppers are known to venture deep into corn fields, particularly those near alfalfa or grasslands.

Minnesota's recent weather pattern, with warm and dry springs and drier summers, has led to a grasshopper boom. Experts advise against treating grasshoppers solely to prevent egg laying, unless economic thresholds are crossed.

For those looking to scout for grasshoppers, the ground count method is recommended, where the population is estimated per square yard. The scouting thresholds can vary based on the crop and the number of grasshoppers. For instance, soybeans can tolerate some leaf defoliation but pod feeding, which directly affects yield, is more concerning.

When scouting soybeans, one should check multiple plants and estimate the defoliation percentage for each leaf. Treatment is considered if defoliation reaches 20% or more.

Regarding management, a variety of insecticides are available. Most insecticides suitable for other soybean pests are also effective against grasshoppers. But it's crucial to keep track of the pre-harvest interval of any insecticide used. As grasshoppers search for more palatable food, they might move out as crops mature.

Farmers are advised to closely monitor fields next spring. A cold, wet spring might decrease grasshopper numbers, but a dry one might see them flourishing again.

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