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Watch Field Edges for Grasshoppers (06/08/17)

Hot and droughty weather is favorable for grasshoppers! So, it is important to watch grasshopper nymphs (young grasshoppers) that are active in field ditches and starting to move into field edges.

Hot and droughty weather is favorable for grasshoppers! So, it is important to watch grasshopper nymphs (young grasshoppers) that are active in field ditches and starting to move into field edges. Nymphs look like adult grasshoppers but are smaller and have wing pads instead of wings. There are usually five or six nymphal growth stages depending on the species of grasshopper and the length of time from egg to adult is 40 to 60 days.

I’ve received a few field reports from the SW area of North Dakota that large numbers of grasshopper nymphs are starting to move into field edges. The NDSU IPM scouts are sweeping field ditches and finding low populations in most areas of the state (see map below), but it is earlier than typically for North Dakota to be seeing this amount of activity. Grasshopper nymphs damage field crops by stripping leaves of crops.

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 Scouting for grasshopper nymphs should be conducted through June. Inspect ditches and field edges 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. Since grasshopper nymph infestations are often the heaviest on the field edges, treating these areas may reduce the total numbers of grasshoppers successfully moving into a field.

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The USDA APHIS grasshopper hazard map for rangeland (see map below) indicates that overall we have low population counts based on the 2016 adult survey. Although no grasshopper outbreaks for rangeland are anticipated for the 2017 season, weather and pasture/forage conditions can affect future grasshopper populations. (Source: D. Hirsch, USDA APHIS PPQ, State Plant Health Director, North and South Dakota). As of June 6th, pasture and range conditions rated 10 percent very poor, 25 poor, 35 fair, 27 good, and 3 excellent in ND (Source: USDA, NASS, ND Crop Progress and Conditions – June 6, 2017 News Release). North Dakota is listed as being abnormally dry to moderate drought in the latest Drought Monitor map. Dry conditions are expected to persist throughout the summer. See the U.S. Drought Monitor website for the latest map. knodel.8

 

 

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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