Grasshoppers and Mormon Crickets Outlook and Management Options

By Sue Blodgett, Extension Entomologist, Montana State University

2004 - Grasshoppers and Mormon crickets are native components of the rangeland ecosystem and are voracious feeders, consuming approximately one-half of their body weight in green forage per day. There are about 12 grasshopper species (called the Dirty Dozen) that are responsible for damage to rangelands. Their populations can reach outbreak levels and cause serious economic losses, especially when accompanied by a drought.

Judging by the Grasshopper Hazard Map for Montana, this year will be an important one for managing grasshoppers in rangeland and cropland around the state. We are seeing grasshopper and Mormon cricket infestations about three weeks earlier than usual this year. The Insect Diagnostic Lab has received reports of grasshopper and Mormon Cricket hatch this year.

Fifteen to 20 grasshopper nymphs per square yard in rangeland or pastures is considered the economic threshold. This number is considered to equate to eight to 10 adults. However, the economic threshold can be modified by weather conditions. If moisture is adequate regrowth of the consumed or destroyed rangeland vegetation may offset the damage. Estimates of daily dry matter intake for grasshoppers range from 30 to 250 percent of body weight compared to 1.5 to 2.5 percent for beef cattle. A 1250 pound cow would consume 19 to 31 pounds of herbage each day. The same amount of herbage could be consumed by 80 - 104 pounds of grasshoppers in a single day.

Management:

The RAATs program developed at the University of Wyoming is an economical method of treating rangeland for grasshoppers in which both the insecticide rate of insecticide and acreage treated is reduced by alternating untreated and treated swaths. There are savings both in the acreage treated and in the amount of product used.

Pesticides in treated swaths kill grasshoppers directly and also provide control as hoppers move from treated to untreated swaths. Predators and parasites are preserved in untreated swaths so that they can suppress grasshopper populations. Recent insecticide trials in Wyoming indicate that reduced rates of carbaryl (Sevin) both in the amount of pesticide and area treated of about 50 percent only reduced control from 85 to 79 percent. This reduction in pesticide would reduce control costs by 60 percent This IPM approach can reduce the cost of control the amount of insecticide used.

RAATs grasshopper control obtained in Wyoming studies found 80-95 percent of a standard, high chemical rate, blanket treatment with 50% cost reduction per acre. This approach is a win-win for rangeland managers by reducing costs, reducing pesticide use and resulting in effective control. A brochure on using this method is available on the web http://www.sdvc.uwyo.edu/grasshopper/ . The RAATS chemical options include carbaryl (Sevin XLR), an insect growth regulator called Diflubenzuron (Dimilin 2L) and malathion. Dimilin interferes with the hopper's ability to molt and must be applied to 2nd 3rd stage grasshoppers. It has been found to very effective but signs of control may take several days (until hoppers molt). It is not effective once grasshopper population has reached adult stage.

Insecticide Options

Rangeland grasshopper control options are covered in detail in the High Plains IPM Guide located on the web at http://highplainsipm.org. Both carbaryl (several formulations of Sevin available) and malathion are available for later season applications, once grasshoppers have reached the adult stage. However, their effectiveness is directly related to residual activity of the product because of the movement and re-infestation potential of adult grasshoppers (residual: carbaryl, 14 days; malathion, 1 day).

Rotational Grazing (from Jerry Onsager):

A long-term strategy to reduce frequency and intensity of grasshopper outbreaks was developed by Dr. Jerry Onsager, USDA, ARS, retired. He examined twice-over rotational grazing compared with traditional season- long grazing for grasshopper outbreak control. Some of his results include:

Large-Scale Grasshopper Spray Programs USDA APHIS has funds to match large-scale grasshopper treatment. Federal rangeland eligible for cooperative grasshopper suppression treatments from APHIS includes: rangeland blocks of more than 10,000 acres that would protect forage as well as prevent re infestation if treated; incipient populations, or hot spots of grasshoppers, that, if treated, would prevent a wider spread of outbreaks; and federal or trust land borders that, if treated, would prevent the movement of economically threatening populations of grasshoppers to adjacent private agricultural lands. Cost sharing includes 100% on federal lands, 50% on state lands and 33% on private lands with the remainder paid for by the landowner.

In many years, federal funds put aside for this type of program are spent or allocated in states to the south before the need for rangeland grasshopper treatment is reached in Montana. However, this year, Gary Adams, Director, USDA, APHIS Montana is putting together programs early so that Montana ranchers and landowners can take advantage of federal matching funds.

Gary Adams can be contacted at: 406- 449-5210 or Gary.D.Adams@usda.gov

Beef: Questions & Answers is a joint project between MSU Extension and the Montana Beef Council. This column informs producers about current consumer education, promotion and research projects funded through the $1 per head checkoff. For more information, contact the Montana Beef Council at (406) 442-5111 or at beefcncl@mt.net

 

Return to regular view	Text-only	Updated: 08/14/2009