Concise Communications |
Dickinson
Research Extension Center 1089 State Avenue Dickinson, ND 58601 |
Grazing Management Can Reduce Grasshopper Problems
Llewellyn
L. Manske PhD, Range Scientist
Amy
M. Kraus, Composition Assistant
Thomas
C. Jirik, Agriculture Communication Editor
North Dakota State University
Dickinson
Research Extension Center
Problems with high numbers of grasshoppers can be reduced with biologically
effective grazing management strategies, says a North Dakota State University
range scientist.
"Grasshopper populations have a history of periodic outbreaks, which can occur
as the outward expansion of a 'hot spot' or as an escalation of low to high
numbers across an area," states Lee Manske, range scientist at NDSU's Dickinson
Research Extension Center. "The periodic outbreaks in the Northern Plains tend
to be associated with drought conditions and heavy grazing on native rangeland
and domesticated grasslands. Little can be done to alter precipitation levels,
but grazing management practices that increase the amount of vegetation cover
can help to control pestiferous grasshopper species and suppress population
outbreaks when weather conditions favor the insects."
Grassland management strategies that repeatedly remove most of the vegetation
reduce plant density and herbage biomass production. Areas with open vegetation
canopy and spots of bare ground are favorable grasshopper habitat, offering
ideal egg-laying sites and basking sites where grasshoppers warm themselves
in the early morning sun to speed metabolic rates and improve growth rates.
Under these grassland conditions, amounts of solar radiation that reach the
soil surface increase, as does airflow over the ground. The resulting increase
in light and decrease in humidity discourage growth of important agents that
cause grasshopper diseases, and the higher soil and air temperatures accelerate
grasshopper egg production, egg development, and the growth and maturation of
the young insects.
Grazing management practices that decrease vegetation cover, as the seasonlong
strategy does, promote grasshopper population increases. Practices that enhance
vegetation cover discourage grasshopper population increases. The twice-over
rotation system on native rangeland is effective in grasshopper management because
the strategy leads to greater plant density and herbage production and fewer
open areas in the vegetation canopy cover.
These plant community characteristics develop because the twice-over rotation
system is biologically effective. It coordinates grazing with grass growth stages
and removes a small amount of leaf material from grass plants between the third-leaf
stage and the flowering stage. This timed defoliation stimulates plant processes
and soil organism activity that enhance plant growth, and the greater herbage
biomass production leads to microhabitat conditions unfavorable for grasshopper
population increases. Compared to seasonlong grazing treatments, the twice-over
rotation system has 25 percent greater grass basal cover, an average of 33 to
45 percent more herbage biomass production during each growing-season month,
and 31 percent less open area in the vegetation canopy.
A recent study confirms that grasshopper populations are lower on the twice-over
rotation treatment than on the seasonlong treatment. Dr. Jerry Onsager, retired
research entomologist, USDA-Agricultural Research Service, followed grasshopper
numbers for five growing seasons on native rangeland areas managed with either
a seasonlong strategy or the twice-over rotation system. The average number
of grasshopper days per square meter was 748 on the seasonlong treatment, considerably
greater than the average of 229 on the twice-over rotation treatment. During
the last two years of the study, a local grasshopper outbreak with an average
density of 22.6 adult grasshoppers per square meter occurred on the seasonlong
treatment. This population outbreak did not occur on the twice-over rotation
treatment, which maintained an average of only 3.9 adult grasshoppers per square
meter.
The improvement in the vegetation characteristics of rangeland managed with the twice-over rotation system yields lower temperatures, higher relative humidity, and reduced sunlight within the grasshopper microhabitat. These changes negatively affect the growth and survival of immature grasshoppers in the nymphal stages and result in reduced grasshopper numbers and in suppression of local grasshopper population outbreaks.
[ Back to 2003 Annual Report Index ] [ Back to Concise Communication ]
[ DREC Home ] [ Contact DREC ] [ Top of Page ]