Grasshopper Outlook For Powder River County

By PR Extension Office

“The good news is that we’ve received much needed moisture and that according to the 2022 APHIS Grasshopper Hazard Map, Powder River County is not in the red zone,” according to Mary Rumph, MSU Extension Powder River County Agent. The map can be viewed at our website: http://www.powderriver.msuextension.org

“That doesn’t mean we won’t be contending with grasshoppers, but it is a strong indication that the population level won’t be as devastating as the past two years,” she added.

According to Gary Adams (USDA-APHIS Billings), the expectation is that the treated areas from last summer will also provide protection this growing season and possibly even longer. What is most important is vigilant scouting.

“I’m hearing reports of grasshoppers…many are already adults that overwintered and are not considered damaging,” said The scouts from APHIS will start looking for new hatches during the end of May and early June. Even then, the grasshopper species that are destructive hatch later in June, weather dependent. The best chance for success is continued moisture for maximum vegetative growth and for potential diseases for the grasshoppers,” continued Rumph.

According to Kevin Wanner, MSU Extension Crop Entomologist, timing for treatment is important during grasshopper outbreaks - pesticides applied too early or too late are likely to be ineffective. Control measures should not be applied until the grasshoppers have hatched and their numbers can be estimated.

Egg hatch can begin during May and can continue through the summer, but timing depends on the species of grasshopper and the weather. David Branson (USDA – ARS Sidney) suggests the grasshopper hatch this year could be delayed by a week or two due to the cool spring weather (unless the upcoming weather becomes warmer than average).

For rangeland grasshopper control, Gary Adams (USDA – APHIS Billings) indicates that optimal timing coincides with the 2nd and 3rd instar stages. Typically, rangeland treatment in Montana occurs during the 2nd to 3rd week of June but could be delayed this year. Specific timing depends on weather and is based on scouting and staging the grasshopper population.

For grasshopper control in crops, Warner does not recommend spraying before most of the eggs have hatched and the pest numbers can be counted. Sprays applied before egg hatch will not have sufficient residual activity. Juvenile and adult grasshoppers can migrate into crops from surrounding grassland, regular scouting is advised through the summer.

Treatment thresholds are based on the number of grasshoppers per square yard. The square foot method of surveying grasshoppers: The number of grasshoppers in a one square foot area is estimated visually and randomly repeated 18 times while walking a transect. The total number of grasshoppers is tallied and divided by two to give the number per square yard. Alternatively, four 180-degree sweeps with a 15-inch diameter sweep net is considered equivalent to the number of adult (or nymph) grasshoppers per square yard (NDSU Extension).

For more information on scouting methods, thresholds and insecticides in rangeland and crops, contact the Powder River Extension Office at 436-2424 or [email protected].