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Grasshopper Populations Surge in Southeastern South Dakota

Grasshopper Populations Surge in Southeastern South Dakota

Large populations of grasshoppers have been detected in Southeastern South Dakota, posing a potential threat to crops as the season progresses. While significant defoliation has not yet occurred, it is important to monitor the situation closely.

The 2023 grasshopper populations are believed to be a consequence of the dry conditions experienced in 2022, combined with a normal to slightly late hard frost and above-threshold grasshopper populations.

Three main species of grasshoppers have been reported in the affected areas of South Dakota: two-striped, redlegged, and differential grasshoppers.

To assess grasshopper populations, two methods can be employed: visual counts or sweep netting. Visual counts involve estimating a square yard in front of you and counting the number of grasshoppers that jump out of the area as you approach slowly. Alternatively, a 15-inch diameter sweep net can be used to capture grasshoppers in four pendulum swings, counting them within approximately one square yard. It is advisable to repeat the sampling method multiple times in a pattern for more accurate results.

The established threshold for grasshopper populations in grasslands, as determined by the U.S. Department of Agriculture, is 15 to 20 nymphs or 8 to 10 adults per square yard.

To scout crops, monitor nymphs and adults along field margins and within fields. Consider management if nymph populations reach 50-75 per square yard, or adult populations reach 21-40 per square yard. In-field management should be considered when nymphs or adults are 30-45 per square yard. Insecticide management should be considered if silk feeding or damage occurs. For soybeans, consider insecticide management if 20% defoliation occurs after flowering or grasshoppers feed on pods.

If grasshopper populations exceed the established thresholds, insecticides labeled for grasshopper management may be employed. Refer to the latest South Dakota Pest Management Guides for a current list of insecticide sprays approved for use in soybeans, corn, and alfalfa.

Poison grasshopper baits can reduce populations in pastures and range areas. However, Nosema locusta spore baits are unavailable for 2023. An insect growth regulator (IGR) containing diflubenzuron can inhibit grasshopper development earlier in the season but should only be used to manage developing nymphs.

Photo Credit: pexels-tudsaput-eusawas

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Categories: South Dakota, Crops, Corn, Soybeans, Alfalfa

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