Wheat growers in areas of the state with high grasshopper densities should avoid planting their winter wheat crops too early this fall.
Large numbers of grasshoppers in areas surrounding wheat fields can threaten seedlings as they emerge, especially in the field margins, says Gary Hein, UNL entomologist at the university's Panhandle Research and Extension Center at Scottsbluff.
"Grasshopper populations decline through the late summer and fall, and in fact, most grasshoppers will die off with the first hard freeze. But that may not be soon enough for the wheat crop because much of our winter wheat will be getting established before the grasshoppers are gone," Hein says.
Determining if a problem will develop is difficult because the standard thresholds for control of grasshoppers in cropland--seven per square yard in the field and 20 per square yard in field borders--must be lowered. The emerging winter wheat has very limited foliage and grasshoppers can easily keep the wheat clipped back completely, causing stand losses, Hein said.
"If grasshopper densities are extreme, it is difficult to completely eliminate the damage," he says. "So, if your area has high grasshopper activity, avoid planting early to reduce damage potential."
Other management may include a higher seeding density in crop borders to compensate for partial stand loss. This may allow for a reasonable stand after grasshopper damage has run its course.
Controlling the adult grasshoppers with insecticides is difficult. "Several control options do exist, though, including planting-time insecticides application or seed treatments to wheat field margins or foliar treatments to areas surrounding wheat fields to prevent grasshoppers from moving into the wheat as it is emerging," he Hein says.
"Grasshopper control around wheat fields can be challenging and the level of effectiveness for any control option will depend largely on the density of grasshoppers," Hein says. "Under very heavy pressure none of the control options will be completely effective, and the loss of some stand on the field margins may be inevitable."
Borders can be replanted later in the fall if grasshopper damage reduces stand in the field margins.
"Grasshopper control in winter wheat will likely be a compromise between effective control and affordability," Hein adds.
More information about grasshopper management options and additional information about planting the winter wheat crop can be found in Crop Watch, UNL Extension's crop production newsletter, at cropwatch.unl.edu or in the UNL Extension NebGuide G1627, A Guide to Grasshopper Control in Cropland, available at a local UNL Extension office or online at www.ianrpubs.unl.edu/sendIt/g1627.html.