UW specialist emphasizes integrated approach for controlling grasshoppers
Riverton – Wyoming has historically been a hot spot for grasshopper infestations, with over half the species in North America taking residence in the state, according to University of Wyoming (UW)Entomology Extension Specialist Scott Schell.
Schell was a featured speaker at the annual Fremont County Farm and Ranch Days held annually in Riverton.
Schell based his research in grasshoppers off 50 years of data and found, in 21 of those 50 years, grasshoppers were at a pest threshold.
“Grasshoppers are very gluttonous and will eat their weight in wet matter every day,” Schell said. “This may not seem like a big deal, but if we have 30 grasshoppers per square yard, that’s 100 pounds of grasshoppers per acre, which is equivalent to a small sheep eating its weight every single day.”
He explained 30 grasshoppers per square yard is not a lot in the grand scheme of things and does not fall within the pest threshold.
A detailed study of 30 years of western grasshopper outbreaks showed the probability, durations and stability of grasshopper outbreaks were consistently higher in Wyoming than in adjacent counties in Montana.
“Grasshoppers can also affect species of concern such as sage grouse,” Schell said. “While sage grouse are omnivorous as juveniles, they eat almost exclusively plants in their older age. Grasshoppers can strip the plants adult sage grouse rely on.”
“Insects are known for their adaptability,” Schell says. “This is why using a single approach is not often recommended or effective.”
“Taking an integrated approach is crucial with any sort of pest infestation,” he said. “Because insects can adapt so quickly to single source approaches, we have to combine methods to be effective.”
Schell explained Extension created the Reduced Agent and Area Treatments (RAAT) approach to controlling the insects.
“We brought down the level of pesticide to where it really only kills the nymphs,” he said. “Aiming to kill adult grasshoppers is really only revenge if they already laid eggs.”
“RAAT takes advantage of the insect’s behavior,” he noted. “Nymphs and adults alike move around a lot in search of food, so even if we don’t kill them with the initial application, they will likely move to a treated strip in search of food.”
Instead of the traditional blanket cover, RAAT treats the field in alternating strips, according to Schell. Under this strategy, if a producer were treating a 1,000-acre lot, only 500 acres would be treated.
“Even if we don’t kill all the bugs initially on the treated strips, they will eventually move to a treated strip,” said Schell. “In this scenario, it also works to our advantage they eat so much because they will likely consume a plant that has been sprayed.”
“The treatment of fields in strips also works to our advantage because it allows for the survival of insect predators of the grasshopper,” Schell explained. “By keeping some beneficial insects alive, we are able to integrate bio-control tactics in addition to the chemical insecticide.”
“Blanket pesticide control can cause more problems in the long-run because it kills natural predators of the grasshopper,” said Schell. “They are also much more expensive.”
In a study published by Schell and fellow entomology colleagues, consistent control of grasshoppers and frequent insecticide treatments contributed to conditions that perpetrate pest outbreaks.
“The use of blanket pesticides also kills non-target insects,” Schell says. “Those insects are a huge help in controlling grasshoppers naturally.”
The study noted though RAATs typically result in a 10 to 15 percent lower efficacy than blanket applications, the reduction in treatment costs is justifiable.
RAATs were also shown to produce better economic returns than traditional blanket applications considering fewer chemicals were actually applied.
Callie Hanson is the assistant editor of the Wyoming Livestock Roundup. Send comments on this article to firstname.lastname@example.org.