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Scout for Grasshoppers (06/02/16)

IPM Scouts have observed very low numbers of grasshopper nymphs (only 1 nymph per square yard) that have just hatched in field ditches in Cass and Barnes counties in SE ND.

Scout for Grasshoppers

IPM Scouts have observed very low numbers of grasshopperent.knodel.grasshopper.photo nymphs (only 1 nymph per square yard) that have just hatched in field ditches in Cass and Barnes counties in SE ND. Young grasshoppers are referred to as nymphs. They are similar to adults in general appearance but are smaller and have wing pads instead of wings. There are usually five or six nymphal stages depending on the species of grasshopper and the length of time from egg to adult is 40 to 60 days.

Grasshopper damage to wheat and other field crops is generally concentrated near field margins. Individual plants will exhibit leaf stripping, beard loss after heading, head clipping, and kernels that have been fed upon or completely destroyed. Later in field season, row crop producers should be aware of the potential for grasshoppers to move into row crops after small grains have begun to dry down.

Scouting for grasshoppers should be conducted through June. Inspect ditches and field margins for nymphs. For grasshopper thresholds, the ‘threatening’ rating is considered the action threshold for grasshoppers in any field crop. For example, grasshopper control is advised whenever 50 - 75 small nymphs per square yard can be found in adjacent, non-crop areas; or when 30 - 45 nymphs per square yard can be found within the field. Since it is difficult to estimate the number of grasshoppers per square yard when population densities are high, pest managers can use four 180-degree sweeps with a 15-inch sweep net, which is equivalent to the number of adult (or nymph) grasshoppers per square yard. Grasshopper infestations are often the heaviest on the field margins. Treating these areas may lessen the total numbers of grasshoppers successfully entering a field.

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Weather is the main factor affecting grasshopper population levels. Outbreaks are usually preceded by several years of hot, dry summers and warm falls, allowing populations to increase slowly. This recent cool, wet weather will favor fungal pathogens that infect grasshoppers and slow emergence. The USDA APHIS grasshopper hazard map for rangeland (see map below) indicates that overall we had low population counts on rangeland in 2015. However, there are a number hotspots in McKenzie County that are localized. No outbreak conditions exist or are anticipated for the 2016 season, but that can change depending on weather and pasture/forage conditions. (Source: D. Hirsch, USDA APHIS PPQ, State Plant Health Director, North and South Dakota). As of May 31, pasture and range conditions rated 1 percent very poor, 4 poor, 24 fair, 65 good, and 6 excellent in ND (Source:  USDA, NASS, ND Crop Progress and Conditions – May 31, 2016 News Release).

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Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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