Grasshopper potential high for western Nebraska rangeland
Large areas of rangeland in the western half of Nebraska are at high risk for serious grasshopper infestations this summer, a University of Nebraska-Lincoln Extension entomologist says.
Ranchers in these high risk areas should be prepared to monitor the build-up of grasshopper densities during the hatching and early development periods from mid-May through June, said Bob Wright, entomologist in the university's Institute of Agriculture and Natural Resources. The high risk category is based on the U.S. Department of Agriculture Animal and Plant Health Inspection Service's 2009 grasshopper prediction map.
Even though the potential is high in these areas, the actual impact of grasshoppers will be largely determined by two factors:
1) Immediately after grasshoppers hatch from their eggs, they have few fat reserves and are vulnerable to cool, wet weather. If they are unable to feed readily during these early stages, high mortality will result, Wright said.
"Since grasshoppers hatch over an extended period, only some of the hatch may be affected. However, this mortality can be significant enough to reduce heavy populations below threshold levels in many areas," he said.
2) The other major factor that will influence this threat is the prevalence of rain. In areas with ample rainfall, fewer problems will materialize because of the increased grass growth, resulting in less stress for grass. Dry conditions that limit grass growth result in a greater demand for the available forage and a greater need to manage grasshopper populations.
If grasshopper populations readily persist through the early hatching period and dry conditions limit grass growth, there likely will be widespread areas with serious grasshopper infestations, and control may need to be considered, Wright said.
"The reduced agent/area treatments, or RAATs, program has been widely used, and ranchers have been very satisfied with the control levels they've seen," he said.
RAATs consists of alternately spraying a swath and leaving a swath untreated so that only half the treatment block is sprayed, reducing treatment costs.
Any of the three insecticides registered for rangeland grasshopper control can be used, but Dimilin has been used almost exclusively with this program in Nebraska. The longer residual of Dimilin (21 to 28 days) allows time for grasshoppers to move from the untreated areas into the treated areas and have contact with the insecticide.
The overall effectiveness of control may be reduced slightly with this method, but the cost will be reduced 50 percent or more. A major cost determinant for using RAATs is the size of the treatment block--larger blocks are much more efficient for applicators to treat. If treatments are warranted, ranchers are urged to work together to treat larger areas to increase the efficiency and reduce treatment cost.
For more information about grasshoppers and their control throughout the growing season, visit UNL's Department of Entomology's grasshoppers website at http://grasshoppers.unl.edu.