With the relatively warm spring that we have had, it is important to start scouting for grasshoppers hatching. Typically, scouting begins around Memorial Day, but it may be a good idea to be on the lookout even earlier this year. USDA-APHIS has predicted Richland County and the surrounding area will again be experiencing high grasshopper populations this year.
Review of the Life Cycle
Grasshoppers deposit eggs in the soil in the fall. These eggs overwinter there and begin to hatch from May through July. Grasshoppers develop through 5 nymphal instar stages. This development spans approximately 30-40 days before they are an adult with fully formed wings. Grasshoppers can live from 40-60 days as an adult. Many of the control options for grasshoppers are only effective when they are in their nymphal stages, making it very important to become familiar with their life cycle.
Scouting
As many know given the high grasshopper populations the past few years, scouting is important as grasshoppers can wipe out parts of or an entire field in a short amount of time. Crop fields should be scouted at least once a week. You can estimate grasshopper populations by counting the number of grasshoppers in a visually estimated square foot area. Repeat this randomly 18 times while walking in a transect, tally the number, and divide by two to get the number of grasshoppers per square yard. In cropland, nymphal counts of 50-75 per square yard in the field margins and 30-45 in field are considered threatening, while counts over those amounts are considered severe and very severe. Adult counts of 21-40 per square yard in the field margins and 8-14 in field are considered threatening and counts over these are considered severe and very severe. Rangeland economic threshold for treatment is 15-20 grasshoppers per square yard.
Control
Grasshoppers are more easily and more economically controlled during the nymphal stages, as they are more susceptible to insecticides, you can prevent their maturation and egg deposition, and you can control them before the adult stage where they are most damaging to crops and rangeland. Unfortunately, cultural and biological control options are generally not effective. Insecticide options include active ingredients such as lambda-cyhalothrin, zeta-cypermethrin, malathion, diflubenzuron, and more. Always read and follow label directions.
For a full list of insecticide options by crop, see the NDSU Field Crop Insect Management Guide or call the Richland County Extension Office, 406-433-1206.
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