Grasshoppers will be out in full force again this season across large areas of the West and Great Plains. Based on fall 2003 surveys, government forecasters predict grasshopper populations will be extreme in some areas of Montana, Nebraska and Texas.
That's a lot of ground to cover. While ground-based spraying to control grasshoppers has been largely disregarded in favor of aerial application, there's a viable alternative to the old truck- or tractor-based application methods, says Jeff Lockwood. He's an entomologist with the University of Wyoming Department of Renewable Resources.
“By combining Reduced Agent and Area Treatment (RAAT) application (see sidebar) and heavy-duty, all-terrain vehicles, we've found a way to suppress grasshopper infestations,” Lockwood says.
Lockwood's been involved in grasshopper research with USDA scientists, state departments of agriculture and weed and pest districts from 1995 to 2000. He says the following application tactics most often optimize economic returns and are recommended by the National Grasshopper Management Board:
Carbaryl (Sevin XLR®) at a rate of 8 oz./acre with an equal volume of water in alternating treated and untreated 100-ft. swaths.
Diflubenzuron (Dimilin 2L®) at a rate of 0.75 oz./acre with 8 oz. of water and 4 oz. of crop oil, in 100-ft. alternating swaths. Or apply at a rate of 1 oz./acre with 16 oz. of water and 8 oz. of canola oil, in 100-ft. swaths alternating with 200-ft. untreated swaths.
Malathion (Fyfanon®) at a rate of 4 oz./acre in 100-ft. swaths, alternating with 25-ft. untreated swaths.
Pest managers say early scouting is essential in grasshopper control, particularly with Dimilin. The insecticide is most effective when grasshoppers are in the second to fourth instar stage of growth — preventing young grasshoppers from molting. The product doesn't harm mammals, birds, fish or non-target insects. And because Dimilin offers up to 30 days of residual control, it works well with the RAAT method.
Cases In Point
More than 75 landowners in western Idaho who participated in an area-wide grasshopper spray program last spring paid $1/acre to protect their grasslands with 1 oz. of Dimilin/acre.
Rauhn Panting, Oneida County Idaho Extension educator, says about 20,000 acres in his area were sprayed — with 40,000 acres protected under the RAAT program.
Costs were $2/protected acre, with the state paying half the cost. Panting says the treatment provided 80-100% grasshopper control, following grasshopper populations as high as 30-45/sq. yd. the previous year.
In some areas of eastern Wyoming, there were 15-60 grasshoppers/sq. yd. in 2002. A large group of landowners there participated in a program to treat more than 260,000 acres of rangeland with Dimilin last spring.
Gail Mahnke, supervisor of the Niobrara Weed and Pest District, says landowners paid $1/protected acre to have their range treated under the RAAT program. The state picked up one-third of the cost.
“Careful scouting assured they sprayed when the grasshoppers were in the second to fourth instar stage of growth,” she says. “This gave us excellent control.”
Using RAAT On Grasshoppers
Reduced Agent and Area Treatment (RAAT) is a method of integrated pest management (IPM) for rangeland grasshoppers. In a RAAT program, the insecticide rate is reduced from traditional levels, and untreated swaths (refuges) are alternated with treated swaths, says Jeff Lockwood, University of Wyoming.
This IPM approach can reduce the cost and the amount of insecticide used by more than 50%. RAAT can be used in either aerial or ground application. And, the method normally results in 80-95% control, which is 5-15% lower mortality than with a standard, high-rate, blanket treatment.
Using RAAT can reduce cost by 50-60% depending on the agent and swath width. Plus, using canola oil rather than crop oil as a carrier may significantly improve the effectiveness of RAAT application.