Large areas of rangeland in western Nebraska were at high risk to grasshopper infestations last year; however, this year could be worse, University of Nebraska-Lincoln entomologists say.
Last year, a wet spring gave rangeland grasses an advantage. So far, the climate predications for this year are calling for warmer and dryer weather this spring. This could put rangeland at a disadvantage.
Once again, 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 2010 surveys conducted by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. Numbers of adult grasshoppers last year are an index of the number of eggs laid, which is the overwintering stage of the most damaging species, Wright said.
Even though the potential is high in these areas, the actual impact of grasshoppers will be determined largely by two factors:
Food availability: Immediately after grasshoppers hatch from their eggs, they have few fat reserves and are vulnerable to cool, wet weather. If they can’t feed readily during these early stages, high mortality will result. 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.
Rainfall: In areas with ample rainfall, fewer problems will materialize because of the increased grass growth, resulting in less pressure for grass. Additionally, wet weather improves conditions for pathogens (e.g., fungi) that attack grasshoppers. Dry conditions that limit grass growth and depress insect pathogens result in a greater value for the available forage and a greater need to manage grasshopper populations. Healthier, more vigorous grass growth equals fewer grasshopper problems.
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, said Jeff Bradshaw, entomologist at UNL’s Panhandle Research and Extension Center at Scottsbluff.