Grasshooper potential remains high in Nebraska
July 15, 2008
LINCOLN, Neb. – Central and southwest Nebraska rangeland are again at high risk for serious grasshopper infestations this summer. Ranchers should be prepared to monitor the buildup of grasshopper densities in these high risk areas during the grasshopper hatching and early development periods from mid-May through June, said Gary Hein, entomologist at UNL’s Panhandle Research and Extension Center at Scottsbluff. The high risk category is based on the U.S. Department of Agriculture Animal and Plant Health Inspection Service’s 2008 grasshopper prediction map.
Even though the potential in these areas is high, the actual impact of grasshoppers in these areas will be largely determined by two factors.
“Immediately after grasshoppers hatch from their eggs, they are vulnerable to cool, wet weather because they have few fat reserves,” Hein said. “Under these conditions, they will be unable to feed readily during their first few days after hatch, and high mortality will result.”
Since grasshoppers hatch over an extended period, only a portion of the grasshopper hatch may be wiped out by these cool, wet conditions, but this mortality can be significant enough to reduce heavy populations below the threshold levels in many areas.
The other major factor that will influence the importance of this potential problem is the prevalence of rainfall. In 2007 these same areas also had a serious potential for problems but few materialized because in many areas ample rainfall resulted in good grass growth, and there was less pressure for grass on the rangelands.
Dry conditions that limit grass growth results in a greater value for the available forage and a greater need to manage grasshopper populations.
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“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,” Hein said.
Grasshopper control using the reduced agent/area treatment, or RAATs, program has been widely used and ranchers have been very satisfied with the levels of control they have seen with this program.
The program consists of spraying a swath and leaving a swath untreated so that only half of the treatment block is sprayed, reducing the cost of treatment. 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 area and contact the insecticide.
The overall effectiveness of control may be reduced slightly with this program, but the costs will be reduced by 50 percent or more. A major cost determinant for the program is the size of the treatment block because 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 the cost of the treatments.
For more information about grasshoppers and their control throughout the growing season, including the 2008 grasshopper prediction map for Nebraska, visit UNL’s Department of Entomology’s grasshoppers Web site at http://entomology.unl.edu/grasshoppers/.