Grasshoppers that emerged this summer could now be a problem to this year's emerging winter wheat, says Jeff Bradshaw, University of Nebraska-Lincoln entomologist based in Scottsbluff.
Emerging winter wheat has very limited foliage so large grasshopper numbers can easily keep the wheat clipped back completely, causing stand losses in field margins, he adds.
While grasshopper populations decline through the late summer and fall, large numbers still can remain after the first hard freeze.
"Growers need to monitor grasshopper densities in areas surrounding wheat fields both before and after planting," Bradshaw says.
Normal threshold densities in areas surrounding cropland need to be lowered because of the damage potential, according to Robert Wright, UNL Extension entomologist.
Densities of 11 to 20 grasshoppers per square yard in non-crop borders surrounding newly planted wheat fields may be enough to cause significant loss.
Several cultural practices also can limit the grasshopper threat:
Avoid early planting in areas of high grasshopper activity. Planting higher risk fields near the end of the optimum planting window will reduce the time that a field will need to be protected from grasshoppers in the fall.
Increase the seeding density of wheat in field margins. This may compensate for partial stand loss and allow for a reasonable stand after grasshopper damage has run its course.
Several insecticide treatments also are available. More information is available at the UNL Department of Entomology's Grasshoppers of Nebraska website at http://entomology.unl.edu/grasshoppers/.
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, Bradshaw 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, he said.
"If grasshopper damage reduces stand in the field margins, these areas can be replanted later in the fall after the first hard freeze and grasshopper populations have declined," he says. "Grasshopper control in winter wheat will likely be a compromise between effective control and affordability."