Grasshopper populations increased "dramatically" in Montana from 2007-2010, from one million acres with more than 15 of the pests per square yard, to 17 million acres with more than 15 per square yard, reports Montana State University.
Crop and rangeland damage has been moderated, however, by the cool and wet spring of 2010 and 2011.
The recent warm dry weather has favored grasshopper development, and based on an August pest audit conducted by USDA, populations appear to remain high across the state.
Continuing warm weather will favor egg-laying behavior and the rangeland hazard will remain high in 2012, according to Kevin Wanner, MSU entomologist, who says winter wheat will be at risk of attack this fall.
Planting winter wheat later in the season is one strategy to mitigate damage caused by grasshoppers, he says. Adult grasshoppers will remain active during the fall season as long as daytime temperatures remain warm.
Later planting dates reduce the window of time that the crop is exposed to the pests. Later planting also reduces the risk of damage by aphids and wheat curl mites, both of which vector viral diseases, notes Wanner.
Extra vigilance in scouting for pest and damage is recommended.
Adult grasshoppers can fly and are very mobile, so localized densities can change quickly, Wanner warns.
Damage thresholds for emerging winter wheat are 3-7 per square yard within the field, or 11-20 per square yard around the field margin. Typically, grasshoppers move into crops from surrounding grassland. In some cases, weeds may attract the pests into fallow fields as well.
When spraying, remember that timing is vital, says Wanner. Border sprays beyond the edge of the crop need to be applied just before the wheat emerges. If it is applied too early, there may not be enough residual.
More help can be found from the Agricultural Research Service at http://www.sidney.ars.usda.gov/grasshopper/.