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Grasshopper
Management: An Integrated Approach
Download Printable version (PDF) GRASSHOPPERS: Can We Prevent Outbreaks? Over the years, grasshopper outbreaks have often plagued farmers
and ranchers in the Great Plains, competing with livestock, wildlife
and humans for food supplies. The most memorable examples occurred
in the 1860s and again in the 1930s when grasshoppers were so abundant
they ate practically everything, including the paint off barn walls.
Under more typical circumstances, grasshoppers consume an estimated
21-23% of the average annual range forage production, a lot, but
maybe not as damaging as it first appears (See "Beneficial
Grasshoppers?!"). However, about every 8-10 years, extensive
outbreaks can decimate range vegetation and lead to a mass migration
to cultivated crops.
In Great Plains rangelands, grasshopper densities tend to increase with drought and grazing intensities, and severe local outbreaks can occur every year. Major grasshopper outbreaks tend to occur during hot, dry weather cycles which lead to drastically reduced range vegetation and increased grasshopper numbers. The grasshoppers then compete with livestock and wildlife for the remaining vegetation. In the past, pesticides have been the primary tools used to combat
grasshopper outbreaks on rangeland, with major infestations often
controlled by large cooperative spray programs. During the last
major outbreak, USDA/APHIS sprayed a record 13 million acres of
public and private land at a total cost of about $25 million.
A similar effort is unlikely to be undertaken today. A lack of government funding and increased environmental concerns and regulations (particularly on public lands) have combined to put a damper on such spraying efforts. Traditional pesticide use appears to be economical on only about 40% of U.S. rangeland even in severe outbreaks, according to economic models. Recently, new approaches have been developed which increase the distance between sprayed swaths while still providing good grasshopper control and cutting application costs by as much as 50 to 60 percent. However, the economic realities of low livestock and commodity prices have made it difficult for any grasshopper spraying to be profitable. But what if producers and land managers were able to reduce grasshopper problems without resorting to pesticides? Building Toward a Solution
The first focuses on how grazing management can reduce grasshopper
outbreaks. That effort has already met with some success. ARS researchers
have been examining how the timing and intensity of livestock grazing
under a twice-over rotational system leads to a significant reduction
in grasshopper numbers when compared to a season long grazing system.
(See "Can Grazing Control Grasshoppers?") The third approach looks at what conditions, such as weather and existing grasshopper densities, lead to larger grasshopper outbreaks, as well as how habitat manipulation, predators and disease might be better used to limit them. Although additional studies are needed, this research points the way toward practical and affordable management techniques for the future.
The Future Ultimately, this research effort will provide both public and private land managers with affordable and environmentally friendly alternatives for grasshopper management. In the future, these management strategies may be the only viable control tactics available for use on significant amounts of rangeland. GRASSHOPPERS:
Are They Beneficial?!
Of nearly 400 known grasshopper species in the Western United States, only about two dozen are considered serious pests. Another dozen are considered somewhat beneficial since they eat undesirable range plants. While it's true that grasshoppers can frequently consume almost a quarter of average annual range forage production, surprisingly that isn't all bad. Since grasshoppers only digest around 12-21% of what they eat from growing plants, much of what they consume is returned for valuable nutrient recycling. Consequently, in low to moderate numbers, grasshoppers may be beneficial under certain circumstances. Moderate grasshopper populations are beneficial in other ways as well. For example, they are an important food source for other desirable species found on the prairies, including many songbirds, game birds and small mammals. Those predators, along with pathogens and parasites, can help keep grasshopper populations low most of the time. Eradication of all grasshoppers would have an unfavorable impact on the food supply for these desirable species, another reason preventative management is a key component of the ARS grasshopper control effort. GRAZING:
Can It Control Grasshoppers?
Although overgrazing by livestock is known to lead to increased grasshopper problems, it's possible that grazing management systems may actually be a key to reducing these problems. Recent ARS research is generating support for that hypothesis. Scientists have found that twice-over rotation pastures average 70% fewer grasshoppers when compared to season long grazing pastures (see graph). Why? Most pest grasshoppers thrive and grow faster when there are many small patches of bare soil which are ideal sites for grasshoppers to absorb energy from the sun. Researchers believe that twice-over grazing causes grass to tiller, which closes up those bare spots and slows the growth rates of many pest species. This slower growth rate likely results in higher death rates for the developing grasshoppers, fewer adults, and less time for the surviving adults to lay eggs for the next year.
Typical grasshoppers go through 5 stages before becoming adults,
with the largest stages eating the most vegetation. Consequently,
if one can reduce the time that grasshoppers are in the larger stages
by slowing their development — one can reduce the impact that
grasshoppers have on rangeland. Although the research is continuing,
habitat differences brought about by grazing patterns clearly appear
to be a key in controlling grasshoppers. While several more years of research are needed, these studies may ultimately provide land managers with new tools that have been shown to be successful under field conditions.
For more Information, contact David Branson at: |
