Growers keep an eye on an increasing threat

Melanoplus sanguinipes, the lesser migratory grasshopper. This species is the most destructive grasshopper in North America.
Photo courtesy of U.S. Rangeland Grasshopper Collection.

Throughout much of the Northwest and Mountain States area, early numbers indicate grasshoppers are going to hit fields and orchards in prodigious amounts. As with everything in farming, weather is the wild card.

Utah is one area that is likely to feel a serious infestation. There are more than 20 species of grasshoppers, notes Diane Alston, Utah State University professor and extension entomologist. The one we can be nearly certain will invade Utah fields this year is the migratory grasshopper. “It is one of the bad ones for crop damage,” she adds.

Insect scouts already have data showing the upward trend. September and October are key times for grasshoppers to lay eggs. Last year was an upswing. The Utah Department of Agriculture predicts two or three more years of high migratory grasshopper populations. Control of populations is a late-spring and early-summer job.

The worst time for growers is when things dry down on rangeland and the grasshoppers head for irrigated farms.

Washington fruit growers might be spared, or they might not. “We’ve seen the buildup in numbers. We had a mild winter and that favors grasshoppers, but we are having a cool spring and that might knock the counts down,” says Rick Zack, entomologist at Washington State University in Pullman, Wash.

When entomologists saw the big buildup coming out of the Plains states, they started doing counts. The threshold for grasshoppers is about eight per square yard. Work at the Washington Department of Agriculture found about 67,000 acres at that level in 2006; by 2009, Zack says, the figure for threatened ground had nearly septupled to 451,000 acres.

“We have indeed been seeing a significant buildup,” Zack says. “Basically, we had no winter, so we’ve put out a precaution. If you had problems in the past, this might be a year for you to look out for grasshoppers.”

In Oregon, it is the clear-winged grasshopper (Camnula pellucida) that is likely to be the problem. Scouting by the seven members of the Oregon Department of Agriculture’s team indicates that Malheur County in the eastern part of the state and perhaps Harney County in the southeast are a focus for grasshopper invasion.

“That is very preliminary data,” says Paul Blom, entomologist with the Oregon Department of Agriculture. They have been scouting since May 17. In mid-June, he said, “The counts we are getting are not reliable because of the weather.” The scouts look at all of the species of grasshopper, but tend to focus on the 10 or so historically major problems.

“Right now it is all about the nymphs [young grasshoppers] and they can have a high mortality,” Blom adds. Grant, Union, Umatilla and Baker Counties will also be on the list.

“We are poised for an outbreak, but that is surprising to me due to the wet, cold spring we had,” says Dustin Johnson, extension agent for Harney County, Ore.

Not everyone has seen the buildup.

“We’re not seeing them in any large numbers in the orchards,” says Shawn Steffan, a postdoctoral researcher at the Washington State University Tree Fruit Research and Extension Center. While most of their IPM trapping is in the canopy and not the grassy understory, so far he has not seen much in the area north of Wenatchee or southeast toward Quincy.

Likewise, Carrie Wohleb, vegetable specialist with WSU Grant-Adams Area Extension, says she has not seen any grasshopper buildup. Like Zack, she notes the cool late spring weather may have kept levels under control.

Another area that will likely be spared is the northwest corner of Oregon, where the land and the local weather are quite different than in the East.

According to Alston, the first line of defense against grasshoppers is to initiate control while grasshoppers are young. “Once they become nymphs or instars they are very difficult to control. When they are small, they don’t need to eat much insecticide to get a lethal dose. Vegetable and fruit growers—anyone with a crop—should start by scouting; look for the little guys,” she says.

“When grasshoppers become adults, they eat much more per day and can fly over treated areas,” she adds. In addition, it takes less material, either natural predators or chemicals, to knock down a young grasshopper than a larger, mature one.

Second, Alston says, growers need to work as a team. She recommends treating as broad of an area as possible as soon as grasshoppers begin to move from nearby open fields and rangelands.

Grasshopper biology

Using the grasshoppers’ history against them is a key to control. Blom notes that Oregon has 50 years’ data on grasshopper patterns. “We focus our scouting on areas that have been past hot spots or where we had high counts in past years,” he says.

Grasshoppers lay their eggs in undisturbed soil in the late summer and fall. Places where there were numerous adults will be a focus for the following spring’s scouting. In May and June, scouts look for nymphs; in July, they look for the adults.

Eggs hatch in the spring and nymphs walk until they find attractive vegetation to feed on. Grasses and forbs growing on open lands satisfy their hunger early in the season, but as populations increase in size and nonirrigated plants dry with warming temperatures and reduced rainfall, grasshoppers move to find lush, green plants to eat. This often means vegetable fields or fruit orchards.

“It’s an unusual spring we’ve had,” Zack says. “They should hatch in early June, but the cool weather [in late May and early June] was detrimental to hatching.”

Mechanical and chemical methods can control grasshoppers. Mowing a wide swath around borders of open fields can reduce migration of grasshopper nymphs walking across the mowed boundary. Insecticides should also be applied to boundaries between open fields, hedgerows, roadsides, drainage ditches and other weedy and unmanaged lands. In order to be effective, mowing and insecticide treatments should be initiated while grasshopper nymphs are small and before their developing wing pads are noticeable.

“The clear-winged grasshopper’s biology lends itself to proactive action,” says Johnson. That species tends to congregate and lay eggs in one area. “That means you can focus control efforts on those areas, but it takes a lot of scouting,” Johnson adds.

Harney County could be the epicenter of outbreak likelihood for Oregon. Last fall, based on the counts done by Oregon Department of Agriculture, Johnson held a meeting to let growers and ranchers know they were on the verge of an outbreak. This spring, he ran a daylong IPM workshop on control and management.

Interest, however, was lukewarm since there was no obvious crisis at hand. Yet getting ahead of the game, as Alston noted, is key. “Being proactive is the only way of managing these grasshoppers,” Johnson says.


Throughout the West, USDA’s APHIS offers assistance for grasshopper control on public lands. When grasshoppers occur in high densities, growers can team up to get state and federal aid to plan and conduct a cooperative management program. Several states offer cost-sharing programs.

Eventually, it comes down to killing the critters.

Zack does not make pesticide recommendations for Washington growers. “My recommendation is to talk to your crop consultant and let them look at the situation and see that what you are doing fits label requirements,” he says.

In general, there are three insecticide formulations that can be used for killing grasshoppers: baits, dusts and sprays. Baits consist of wheat bran combined with the insecticide carbaryl or a natural grasshopper pathogen, Nosema locustae. Baits should be spread evenly throughout the boundary habitat, and grasshoppers will consume the bait as they forage, Alston says.

Baits selectively kill only grasshoppers and other foraging insects. However, Alston notes that baits are not a one-time application and typically must be reapplied following rainfall or irrigation. Examples of carbaryl bait brands include Lily Miller Grasshopper Bait, Sevin 5 Bait and Eco Bran 2 percent. Baits containing the natural pathogen include NOLO Bait Biological and Planet Natural Semaspore Bait.

A number of insecticide sprays suppress grasshoppers, including malathion, permethrin (Spectracide, Bonide Eight, Basic Solutions), bifenthrin (Allectus, Brigade, Sniper, Talstar) and carbaryl (Sevin). Some products are not for use on edible plants and some are restricted to licensed applicators only, so be sure to read the product label.

Since the migratory grasshopper frequently starts its life on BLM managed rangeland, federal, and often state, governments also have a spray called dimilin, a growth regulator. Applied early in the grasshopper’s life cycle, it interferes with shedding their exoskeletons and molting to the next stage. USDA’s APHIS is charged with managing those pests on federal land.

Sprayable formulations tend to be less expensive, Alston notes. They kill both on contact and when grasshoppers eat the treated vegetation. On the downside, sprays are not selective and can kill beneficial insects, pollinators and other susceptible animals, so careful application and appropriate timing are important to protect non-target animals.

Carbaryl (Sevin) is the only type of dust registered for farmhouse yard application. Dusts are easy to apply, but are more expensive than sprays and must be reapplied after rain or irrigation, Alston says.

Blom notes that the department’s 2011 efforts will be based on 2010 adult findings. “Then you take your best guess, focusing on areas where there has been past activity,” he says.

“It’s a good year to keep your eyes open, especially if you have had grasshopper problems in the past or you abut BLM or range- land,” Zack concludes.

Watch for Mormon Crickets, Too

In addition to this year’s migratory grasshopper threat, growers are also likely to face a bumper crop of Mormon crickets.

Despite all the research studies that have been done, nobody has yet come up with a definitive explanation of why Mormon crickets and migratory grasshoppers have their boom-and-bust cycles, according to Diane Alston. “There is not yet a definitive recipe for their perfect storm,” she says. Weather is a key.

Unlike cicadas, which follow an inner clock in their cycles, grasshoppers and Mormon crickets do not have the same thing. Cicada cycles allow host vegetation to regrow and predators to fade.

Alston says the insects tend to do better following a droughty or dry period. “That is related to egg survival,” she says. “Dry periods also decrease food availability.”

Winter snowfall makes a difference, too. A winter with many freeze-thaw cycles or a hard winter will hurt both Mormon crickets and grasshoppers.

Curt Harler is a freelance writer and a frequent contributor to Moose River Media. He resides in Strongsville, Ohio.