When local ranchers find themselves up to their ankles in grasshoppers, Darrin Pluhar knows it’s time to fly into action. For several years, his choices for rangeland grasshopper control have been a short list of insecticides – malathion, acephate (Orthene®), methyl parathion (Penncap M®) and carbaryl (Sevin®).

Pluhar is the owner of Plu’s Flying Service of Miles City, MT. He’s among a growing number of folks on the front lines of the hopper war who have added to their arsenal a new tool in rangeland grasshopper control – Dimilin®. Other insecticides are labeled for control of grasshoppers in forage grasses, alfalfa and crops.

“Everything considered, Dimilin is a great product for grasshoppers,” says Pluhar. “If we have a year like 1997 – the last year hoppers were really bad here – Dimilin would be a no-brainer.”

This year, because of a cool spring, Pluhar says grasshoppers might be set back a few weeks in his region.

“We really have no idea of what we’re going to face until hoppers start showing up,” he adds. “It’s just a matter of watching and then moving fast when you decide there are enough under the right conditions to do damage.”

The U.S. has more than 700 different species of grasshoppers. Among the 40 or so that can damage crops, the most damaging to rangelands are the migratory (Melanoplus sanguinipes), bigheaded (Aulocara elliotti) and whitewhiskered (Ageneotettix deorum) grasshoppers.

Outbreaks of grasshoppers and Mormon crickets (Anabrus simplex), a ground-dwelling katydid found in western Rocky Mountain basins, have historically occurred in the 17 states that lie on or west of the 100th meridian. In 2001, they caused an estimated $25 million damage to crops in Utah alone.

Rancher Craig Randall, Broadus, MT, has had experience with grasshoppers. In 1998 he sprayed 10,000 acres of rangeland for grasshoppers. He wishes Dimilin would have been available.

“We’d have had a better kill – and it’s definitely safer,” he says. Now, after two years of experience with Dimilin, he’s ready to roll with it again if necessary.

As a growth regulator, Dimilin disrupts the nymph’s ability to molt and affects a young grasshopper’s coordination and feeding habits. Dimilin is also effective on Mormon crickets, primarily a pest on croplands, but they can damage rangelands when at very high populations.

Observation Is Key

“The best thing a rancher can do is get out early and look around,” advises Randall. “But, you have to be a good scout, otherwise you’re throwing you’re money away no matter what material you use.”

He says economic thresholds are very tough to figure.

“It’s a matter of past experience – and getting to grasshoppers early.”

Greg Jackson, of Wheatland, WY, says it takes a few days to begin seeing results with Dimilin, but it’s “rainfast” and can provide up to a full month of residual control.

“We sprayed 10,000 acres with Dimilin last year,” says Jackson, an aerial applicator. “Within two to three weeks, the areas we sprayed were almost void of grasshopper activity.”

Cost of control is the first thing customers ask, Pluhar and Jackson say.

“We’re looking at less than $2 per treated acre for Dimilin, not including application costs,” says Pluhar. “And because it can be applied in alternating treated and untreated swaths, costs can be cut in half.”

This strategy for rangeland grasshoppers is called Reduced Agent/Area Treatment (RAATs). The ultra-low volume product can be aerial applied at 8 oz./acre – half normal rates.

Randall says Dimilin poses no risk to wildlife, birds, fish or nontarget insects, including honeybees. But, the restricted-use pesticide is toxic to some aquatic invertebrates and should not be applied by ground within 25 ft., or by air within 150 ft., of water bodies. Care should be taken to avoid drift and run-off that may reach aquatic organisms.

Ranchers also may need to consider other registered insecticides for spraying protective “barriers” around crops and valuable forage production areas, such as hay meadows, seeded crops like alfalfa or annual forages.

For more information on grasshopper identification and control, check out http://scarab.msu.montana.edu/ hpipm/ and www.sdvc.uwyo.edu/ grasshopper.