Farmers and ranchers in northern Utah battle swarms of voracious grasshoppers each year. The damage adds up: A single grasshopper eats its body weight in wet vegetation daily and wastes six times more additional plant matter.

If there are 30 adult grasshoppers per square yard, that is a total of 100 pounds of grasshoppers per acre. This is like each acre hosting a sheep daily eating its body weight in forage daily, and also wasting six times that amount. Or perhaps there are only 14 grasshoppers per square yard; this adds up to 30% forage loss of northern mixed-grass prairie over the growing season.

The West’s semiarid climate provides the perfect environment for grasshoppers to flourish. “The grasshoppers hatch up high on benches and mountains,” explains Josh Dallin, Box Elder County’s Utah State University Extension assistant professor. “Then, they work their way down to the irrigated fields in the valley. They proliferate with lush feed, dry weather and hot temperatures.”

Grasshoppers clouded the Cache Valley of northern Utah and southeast Idaho in 2018. “There were so many grasshoppers squashed on the highway, it looked like a manure spreader went down the road and lost its load,” Dallin recalls. “Grasshoppers leave a field looking like it’s been ‘weed-eated.’ You can tell which direction the grasshoppers came from, and where they’re headed. Producers that didn’t spray for grasshoppers lost 100% of their crops and forage.”

In other areas of the Rocky Mountain West, grasshoppers aren’t an annual problem but do cycle to pest-level. Wyoming had a dense outbreak in 2010. The level of grasshoppers in the state in 2018 (those insects which laid eggs ready to hatch the next spring), prompts Wyoming ag producers to gear up to treat grasshoppers in 2019.

Reaching pest level
Most pest grasshopper species univoltine, which means they have one complete life cycle per year. This seems like a good control of population; but, for instance, the differential grasshopper can produce up to 194 eggs per pod. “If you had 40 of this specie per square yard,” says Scott Schell, University of Wyoming Extension entomologist and chairman of the National Grasshopper Management Board, “and 20 of them were female, and if they each only laid one egg pod, that’d be 900 eggs per square yard ready to hatch next year.”

Eggs, which are set in the upper inch of soil, are crushed by tillage and drowned by flood irrigation — “except for the clear-winged grasshopper, whose eggs can withstand submersion in water for quite a long time, and hatch when water subsides,” Schell cautions.

Immature grasshoppers emerge from egg pods en masse, which will overwhelm predators if the egg survival rate is high. “As with most pest insects,” Schell says, “grasshoppers lay enough eggs each year to be a problem if all eggs hatch. But there are weather events and predators that keep the population in check most of the time.” Because there are multiple pest species of grasshoppers with eggs that hatch at different times from early spring to early summer, you need to survey for the hatching pest grasshoppers and treat as often as necessary to prevent crop damage later.

Grasshoppers and consistent challenges
Producers in northern Utah spray for grasshoppers every year but rarely see a dent in the population. Dallin theorizes the nymphs aren’t hit by the controls. “When grasshoppers are immature in our area, they’re up on federal lands, which often aren’t treated. The grasshoppers don’t move down into the valley’s deeded land until they’re adults,” he explains.

To control pest grasshoppers, it’s very important to treat them at the nymph (immature) stage. Nymphs are smaller than adult grasshoppers, and either wingless or with reduced wings. To identify the grasshopper threat at nymph stage, scout your pastures, fields and borrow ditches throughout the spring. Schell considers 15 to 20 nymphs per square yard an action threshold to apply treatment to prevent grasshoppers from causing economic injury.

The University of Wyoming advocates the reduced agent and area treatments form of integrated pest management. “RAATs is a level of insecticide targeted for nymphs,” Schell explains. “If your grasshoppers are already adults, they’ve done most of their feeding damage and laid their eggs. When you treat adults, all you do is get revenge. You don’t manage them.”

RAATs capitalizes on grasshoppers’ natural movement by alternating chemically treated strips of rangeland, irrigated pasture or cropland with untreated strips. Strip treatment — 100-to-150-foot-wide swaths — lowers the costs, but still controls grasshoppers because they hop around. It also maintains enough grasshoppers to feed beneficial predator insects and nesting birds. If grasshoppers were eradicated completely by chemical treatment, their predators and parasitoids would decrease for lack of food. Then, these natural predators and parasitoids wouldn’t be alive to help prevent future grasshopper outbreaks.

Utah State University is researching if it’s possible to predict grasshopper populations. “Recently, we just have bad years [of grasshoppers] all the time,” Dallin says. “It doesn’t seem like a cold, snowy winter, a cold, wet spring or a warm, dry winter make any difference in population.” That’s why scientists now compare decades of weather pattern data with corresponding records of grasshopper plagues. “It’d be helpful to producers to know if certain weather will bring more grasshoppers,” Dallin says.

Taking a look at grasshopper control
Entomologists have long reviewed methods for combating grasshoppers. Add in rising concern about insecticide load in the environment, and there’s work to strike a balance. Here’s a look at controls, and even a handy calculator for grasshopper control.

Using the reduced agent or area treatment approach can lower insecticide exposure and continue to provide results.

Blanket vs. RAATs: checking the control method
Grasshoppers are easily controlled by the lower percentage rates of mortality of the RAATs method. There are exceptions to RAATs’ usefulness, however. If grasshoppers reach the late instar nymph stage, full-coverage application and higher rates may be needed. Also, the RAATs guide may not work if grasshoppers are extremely thick or forage cover is tall and dense or if the terrain is rough.

Canola oil for grasshopper control
University of Wyoming research found that using canola oil as part of the spray adjuvant increased grasshopper control when using the RAATs strategy. The canola oil is an attractant to grasshoppers. “When you see dead grasshoppers on the road with live grasshoppers,” Schell explains, “the live ones aren’t applying first aid to their fallen brothers. They’re eating the dead ones for their fat content. Fatty acids are vital to grasshoppers. They can’t manufacture them, so they have to eat fat in their diet.”

The addition of canola oil to only a 0.75-fluid-ounce rate of diflubenzuron per acre provides good control. If petroleum-based oil or methylated seed oil alone are used as the spray adjuvant, it is recommended to use 1 fluid ounce of diflubenzuron per treated acre to get good control. This is less than the full label rate of 2 fluid ounces, but has still been found to work well on rangeland grasshopper outbreaks.

Treatment toxicity rates
Carbaryl, malathion and diflubenzuron are the three most common rangeland insecticides used in grasshopper control. Research by Oregon State University shows that diflubenzuron is the least toxic to mammals, birds and fish. Studies also report repeated exposure of bee colonies to Dimilin L2 (a brand name of diflubenzuron) at application rates of 57 to 140 grams active ingredient (a.i.) per acre presented no harm to adult honeybees or their broods. For comparison, a single Dimilin application of 7 grams a.i. per acre controls grasshoppers.

Hemken writes from Landry, Wyo.