A Swarm of Grasshoppers Is Invading Montana Hemp Fields
A grasshopper grazes on a hemp bud.
All photos courtesy of Gregg Gnecco/IND HEMP

A Swarm of Grasshoppers Is Invading Montana Hemp Fields

Entomologists and growers who have reported severe crop loss share insights on how to combat the hungry and damaging critters.

September 8, 2020

Julia Meissner was hoping this year would be better than the last.

Much of the 140 acres of hemp she planted for cannabidiol (CBD) in 2019 on her farm, M&V Farm and Ranch in Chester, Mont., was taken out by a hailstorm.

This year, she has a contract with IND HEMP, a hemp oilseed and fiber processing company, to grow 700 acres of organic hemp for its seed and stalk. Her field looked lush and green by July, and she felt confident she’d have a decent crop for sale.

Then, the grasshoppers came.

As if on cue, Meissner says the critters moved in as the plants reached maturity in the middle of July. At first, they chewed on the large leaves near the bottom—it was minor damage, but ultimately redeemable. 

The real trouble began as they worked their way up, eating the leaves that held the bud and seeds in place, knocking them to the ground like coins falling from holes in a pocket. Once they’d stripped the leaves, they began gnawing on the hemp’s fibrous stem.

Meissner’s irrigation pivots have, for the most part, prevented the grasshoppers from heavily damaging a bulk of her field. But the surrounding parts of her hemp field untouched by the pivots are brown with damage.

“It’s just sticks—60 acres of just sticks,” Meissner says. “We are definitely seeing the dollar signs disappear. … In 14 years, I’ve never seen grasshoppers like this.”

The voracious critters are moving through the northern part of Montana, and they have taken a liking to hemp (although entomologists Hemp Grower spoke with say grasshoppers will eat just about any plant.) Benjamin Brimlow, an agronomist with IND HEMP, says several of the roughly 35 farmers he’s working with this year have been hit severely. 


“We’ll be able to recover most of our acres. The hard thing is some farmers’ fields are completely lost—zero. They’ve been eaten down to the nub,” Brimlow says. “What should look like a green stand looks like a wheat stubblefield. The fields that got hit are just annihilated.”

Gregg Gnecco/IND HEMP
Before and after a swarm of grasshoppers ate through a hemp field in Montana.

Ripe Conditions

The western U.S. is well acquainted with the destruction grasshopper swarms can bring. Grasshopper outbreaks are typically prevalent in the Mountain time zone states, says Whitney Cranshaw, a professor and extension specialist with Colorado State University’s College of Agricultural Sciences. In late June of this year, the U.S. Department of Agriculture (USDA) announced $3 million in additional funding to suppress swarming populations in Arizona, Idaho, Montana, Nevada, Oregon, South Dakota, Utah, and Wyoming.

Brimlow says grasshoppers are prevalent across the entire state of Montana this year, but they’re especially rampant in the northern part of the state. In late June, the U.S. National Weather Service said meteorologists in Glasgow, Mont. may have picked up the swarms on their radar, mistaking them for weather patterns (though it’s unclear whether those are the same species invading hemp fields this year). 

Swarms of grasshoppers are often a result of a perfect concoction of weather and ecological conditions that take place over the year. 

“Every year is an independent kind of event depending on weather and the effects of natural enemies,” Cranshaw says. “The classic situation where you’re going to have a grasshopper problem is when you have enough spring moisture so that everything is nice and green, so the eggs hatch and the grasshoppers do well and grow. Then, the rains stop and it gets [dry].”

Brimlow said Montana’s weather roughly followed that pattern.

“It wasn’t an extremely wet fall, it wasn’t extremely dry spring, but it was enough of all three that the level [of grasshoppers] were able to just blow up,” Brimlow says.

The result has been a mass of the extraterrestrial-looking creatures hopping among not just hemp, but also nearly every crop grown in Montana. 

Brimlow describes the scene in hemp fields: “You drive up the field road, and you look in front of the truck, and there’s almost this cloud moving from a bare stubble field. You just see this net positive wave of bugs flying low as far as you can see into a green hemp field. Then, you get out, and the grill on your truck smells like cooked insects. Then, you walk into the field, and wherever you turn, wherever you walk, they move just a couple feet ahead of you, leaping off of stems. And it’s just this 360-degree wave wherever you go.”

Benjamin Brimlow shows how water affects grasshoppers' feeding habits as the critters swarm the field. (Video courtesy of Gregg Gnecco/IND HEMP)

Grasshoppers on Hemp

Cranshaw has been extensively studying hemp pests, including grasshoppers, since 2015. 

While thousands of species of grasshoppers exist, more than 120 live in the western U.S. states. Just a fraction of those are considered pests.

To date, six types of grasshoppers have been confirmed to feed on hemp, according to a University of Colorado fact sheet.

“It’s important to understand that there are some kinds of grasshoppers that can cause damage to hemp, but many others wouldn’t touch hemp,” Cranshaw says. “Five percent of all kinds of grasshoppers are the ones that could cause damage to crops.”

Even spotting large numbers of grasshoppers in the field doesn’t necessarily mean they will be problematic. Cranshaw says some grasshoppers feed on weeds in the field instead of the hemp. 

A farmer shows off the damage from a 

grasshopper outbreak.

Generally, hemp can tolerate some leaf loss and moderate levels of defoliation with little effect on its yield. Younger hemp crops are typically more susceptible to damage. But Cranshaw says that two species of large grasshoppers in particular are damaging even to mature hemp: the differential grasshopper and the twostriped grasshopper.

“The big damage I have seen has been from these two species of grasshoppers that roost on the plant overnight and spend a lot of time just chewing on layers of stems and girdle them,” Cranshaw says. “They die back from that.”

Chemical control options are limited for grasshoppers because few can penetrate their thick exoskeletons. Control options for hemp are even more limited, as only 36 pesticides have been approved by the U.S. Environmental Protection Agency (EPA) for use on hemp to date. Some states, such as Montana, have even more stringent limitations on the pesticides approved for hemp. 

Brimlow says he worked with the Montana Department of Agriculture to try fast-tracking approval to use an insecticide called PyGanic on the grasshoppers, but the EPA denied the application.

For this year, Montana hemp farmers’ primary options for removal have been mechanical.

Quelling the Critters

Meissner discovered that irrigation disrupts the grasshoppers’ feeding. She’s been running her pivots 24/7.

This option is, of course, costly. Meissner is lucky to live near a river to draw water from, but she’s had to fill her generator every day with 400 gallons of fuel, as opposed to twice a week as she would do normally. (This option is also risky, as hemp does not like to be constantly wet.)

Meissner says she’s also spent a significant amount of money on organic sprays to use surrounding the field in an attempt to stop the grasshoppers before they reach the hemp. But even that hasn’t completely kept the critters at bay.

“We’ll be lucky if we get 50% of what we thought we were going to get,” Meissner says. “I’m sure we’re going to lose $500,000 on the crop itself.”

For control of a current infestation, Raymond Cloyd, Ph.D., a professor and extension specialist with the Kansas State University Department of Entomology, says mechanical removal is the best option. He suggests growers pick them off and either squish them or dunk them in soapy water (or send kids into the field with badminton rackets to swat them away). He’s also seen some growers send chickens into the field to eat them.

Weed control also helps.

“There is no silver bullet,” though, Cloyd says. The most effective solutions, as with many other things, are preventative. 

Cranshaw says grasshoppers lay eggs in untilled areas, so growers shouldn’t plant their hemp next to an untilled field. If untilled areas are nearby, Cranshaw suggests planting less profitable crops or plants around the edges of the hemp field. Grasshoppers have many natural predators, so the more time it takes grasshoppers to reach the hemp, the less chance they have of surviving long enough to make it there. 

“The closer you are to untilled field edge, the more grasshopper pressure you’re going to have,” Cranshaw says.

Cranshaw also says organic growers can use a fungus called Nosema locustae (branded as NoLo Bait) to spray the surrounding areas of the field, although it’s “not hugely effective but can help.”

Benjamin Brimlow of IND HEMP stands in an eaten hemp field.

Brimlow says he plans on working with farmers proactively early next year to reduce risk by utilizing a tool from the USDA that predicts where outbreaks are likely to occur. He also plans to encourage farmers to use the NoLo Bait.

The good news is that grasshoppers cannot survive the winter, and Cranshaw says an outbreak one year does not mean a severe outbreak will occur the next year.

Despite the devastation brought on by the grasshopper swarm, Meissner and Brimlow say Montana farmers know growing in their state is a risk. True to the “Wild West,” Montana’s storms and pests can be fierce.

“We have a lot of different options for income, and a lot of ways to lose money,” Meissner says. “You just move forward. There’s always next year.”

Benjamin Brimlow shows the devastation on a field after it was ravaged by grasshoppers. (Video courtesy of Gregg Gnecco/IND HEMP)