May 11, 2007

Central and southwest Nebraska rangeland are at a high risk for serious grasshopper infestations this summer, University of Nebraska-Lincoln entomologists say.

With grasshopper hatch starting in mid- to late-May, ranchers should begin to monitor grasshopper densities in high-risk areas from mid-May through June, said Gary Hein, Institute of Agriculture and Natural Resources entomologist at UNL's Panhandle Research and Extension Center at Scottsbluff.

The high risk category is based on the U.S. Department of Agriculture's Animal and Plant Health Inspection Service grasshopper prediction map.The good news is that damage from grasshopper populations can be modified by weather conditions across the state, Hein said.

Recent rains through some of the high-risk rangeland areas will increase grassland production and allow for better forage production, Hein said."Increased forage means less impact from grasshopper feeding as well," Hein said.

The greatest impact on grasshopper populations is from cool, wet weather during grasshopper hatching periods, he said.

"Immediately after grasshoppers hatch from their eggs, they are vulnerable to cool, wet weather because they have few fat reserves," Hein said.So, if the grasshoppers are unable to feed readily following hatching, they will die.

Since grasshoppers hatch over an extended time, only a portion of the grasshopper hatch may be wiped out by cool, wet weather conditions.

"However, this mortality rate can be significant enough to reduce heavy populations below the economic threshold levels in many areas," Hein said.

Usings RAATs for Control

Serious infestations can be controlled using the reduced agent/area treatment, or RAATs, program, said Jack Campbell, entomologist at UNL's West Central Research and Extension Center at North Platte.

"This program has been widely used and ranchers have been very satisfied with the levels of control they have seen with this program," he said.

The RAATs program consists of spraying a swath of grass and leaving a swath of grass untreated so that only half of the treatment block is sprayed, reducing the cost of treatment.

This program can be used with any of the three insecticides registered for rangeland grasshopper control; however, Dimilin has been used almost exclusively in Nebraska. Dimilin has a longer residual of 21 to 28 days, allowing grasshoppers to move from untreated areas to treated areas and contact the insecticide.

The overall effectiveness of control may be reduced slightly with this program, but the costs will be reduced by 50% or more. An important cost determinant for RAATs treatments 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 totreati large areas.

For more information about grasshopper control visit UNL's Department of Entomology's Grasshoppers of Nebraska Web page at http://entomology.unl.edu/grasshoppers.

Sandi Alswager Karstens
IANR News Service