If grasshoppers weren’t invented in southeast Wyoming, they should have been. The area has long been a hot spot for grasshopper infestations, with populations reaching 25-30 insects/square yard – three to four times the economic threshold established by experts at the USDA's Agricultural Research Service.

Grasshoppers destroy an average of 25% of available forage in the Western states each year, says Jeff Lockwood, University of Wyoming entomologist. In Texas alone, Lockwood estimates grasshoppers consumed an estimated $190 million in grazing land.

In Wyoming in 1999, damage to rangeland was so severe that local officials declared Platte County a disaster area.

For ranchers accustomed to paying up to $5/acre for grasshopper control, the offer the Platte County Weed and Pest Control Office made in 1999 was almost too good to believe.

For a cost of just $1/protected acre, landowners in the county could sign up to have their rangeland treated with an insect growth regulator called Dimilin. And, as long as the material was aerially applied using an innovative method of spraying alternate swaths, the county agreed to pick up any expenses that exceeded $1/protected acre.

"Dimilin is a new product for grasshopper control, and some of our landowners were a little skeptical when we told them we intended to treat every other swath by air at a low rate of just 1 oz. per protected acre," says Bob Shoemaker, Platte County weed and pest supervisor. "But once they saw how well Dimilin controls juvenile grasshoppers, they were sold. We ended up protecting about 40,000 acres under the program in 1999 and another 20,000 acres last season."

Dimlin was recently registered for control of grasshoppers and Mormon crickets on range grass, rangeland, and noncrop areas. It’s an insect growth regulator that affects the formation and deposition of chitin in the insect’s exoskeleton.

Applied when the grasshoppers are in the second and third instar stages of growth, Dimilin leads to fatal or defective, incomplete molting. The eggs laid by adult female grasshoppers that consume Dimilin may not hatch, and adult females can have a shortened life span.

"Last summer, we began spraying in mid-June, and I’d say we got at least 90 percent control," says Shoemaker, who also serves on the board of the National Grasshopper Management Board. "Where we sprayed with Dimilin, we found an average of just one or two grasshoppers per square yard."

Labeled for use at a rate of no more than 1 oz./acre (fluid), Dimilin is extremely effective at very low rates. The Platte County program combined Dimilin with 4 oz. of crop oil and water to apply between 12-24 oz. of spray solution/acre.

Applications were made using the Reduced Agent and Area Treatments (RAATs) method of treating every other swath. Designed to reduce both the cost of control and the amount of insecticide used, the RAATs program relies on the migratory habits of grasshoppers to control the insects as they move from the untreated to treated swaths.

Greg Jackson, who was hired to make the applications, broadcast-applied the material, flying 100-ft. swaths at about 100 ft. above ground level. Jackson says he was surprised at how little Dimilin it took to knock down the grasshopper populations.

"I’ve treated rangeland for other customers with Asana, which does a good job but costs about $11/acre including application costs. In 1999, we treated some Bureau of Land Management (BLM) land with malathion under the RAATs program. But a week later, it was full of grasshoppers again.

"After we put out the Dimilin, you’d still find a few grasshoppers that had lost their legs, but within a few days, the land was almost void of grasshoppers. The landowners that I talked to were very happy with the results," Jackson says.

Environmentally Safe

Dimilin is nontoxic to birds, bees, fish, earthworms and non-target beneficial insects. Effective at an active rate 100 times lower than other materials labeled for grasshopper control, Dimilin also exhibits very low mammalian toxicity, making it safe to use around humans, livestock and other mammals.

"Dimilin is super safe to the environment and doesn’t affect birds, fish or livestock," says Shoemaker. "And, unlike malathion, we don’t have to leave a mile buffer zone around bee fields and bee yards, which can leave huge holes in your control blocks. Dimilin is far and above safer to the environment than any of the products we’ve used in the past."

Lining Up For 2001

Jackson says he’s already received phone calls from property owners asking how they can participate in the grasshopper control program. The county intends to extend the cost-sharing program another year.

"There are still some breeding sites and hot spots of grasshopper activity that we’d like to clean up," says Shoemaker. "And it would help if the federal government would let us use Dimilin on the BLM land, which represents about 30 percent of Platte County.

The program is accomplishing exactly what was hoped, Shoemaker says, which was to achieve long-term, grasshopper population control.

"I think we’re finally turning the grasshopper cycle around," he says. "And because Dimilin is so effective at low rates, the cost to the county has only run about 15-20¢/protected acre beyond the $1/acre landowners are paying."

Jerry Schleicher of The Duff Co., Kansas City, MO, produced this article on behalf of the public relation firm's client Uniroyal Chemical.