Grasshoppers of Montana:
Grasshoppers are a common pest in Montana, with around 400 species present in the state. Thirteen of these species are known to cause economic damage to crops. Some of the economically damaging species include the migratory grasshopper, clear-winged grasshopper, and white-whiskered grasshopper. Most grasshopper species overwinter as eggs in the top inch of soil, except for species like the speckle-winged grasshopper, which overwinter as adults and are not considered economically damaging pests. If grasshoppers with fully formed wings are observed in spring, they are likely not of economic concern as the species that cause damage overwinter as eggs. Identifying grasshopper species in their nymphal stage can be challenging, but scouting for grasshoppers focuses on determining life stages and locations rather than specific species. Populations are typically higher outside of the field, so scouting methods differ between edge habitats and within the field. Scouting at the edge habitat involves counting the number of grasshoppers that jump into or out of a randomly selected one square foot area, while within the field, the count is done in a one square yard area. Economic thresholds vary, with the general threshold at the field margin being 50 to 75 nymphs per square yard or 21 to 40 adults per square yard. Within the field, the threshold is lower at 30 to 45 nymphs per square yard or 8 to 14 adults per square yard. These thresholds are not specific to any particular crop.

Control Options:
Biological, chemical, cultural, and mechanical control options are effective at various points of the year. Biological control agents include species of bacteria, fungi, microsporidia, nematodes, predators, and viruses. One can amplify the presence of biocontrol fungi, Nosema locusta, by using Nolo Bait (ARBICO Organics) in their gardens. However, this product is not recommended for large-scale applications and is currently out of stock. Chemical control includes Asana XL, Dimilin, Fyfanon, Lumivia CPL, Mustang Maxx, Orthene, Pyganic, Sevin, and Warrior II. Dimilin is a highly effective early-season control tactic in range and pasture, with a low impact on beneficial insects. Asana XL and Warrior II are labeled for grasshopper management for both range and pasture and field crops, meaning that their label is more versatile. Please review the chemical label prior to purchasing and/or use of the product. Cultural control includes early planting, crop rotations, and grazing rotations. Mechanical control includes tillage in the early spring and fall. Although tillage reduces soil moisture, it is a source of egg mortality. Unfortunately, there is no economic threshold established to determine if tillage is needed.