Reports of the Fall Armyworm date back to the 1700s. At that time, American newspapers were reporting widespread outbreaks, as these pests lived up to their namesake – marching across fields in the hundreds of thousands, devouring plants and leaving devastation in their wake.
In 2021, the pest has shown its might again, reaching the largest population in 30 years and spreading across the United States from the southeast and northeast to the Midwest.
“It’s an epidemic pest,” said University of Missouri entomologist Kevin Rice at the University of Missouri crop management conference. He said farmers should expect an influx of army worms every 30 to 50 years. Given this timeline and the severity of armyworm pressure in 2021, many farmers and ranchers wonder if there will be a repeat in 2022.
Rice said the FAW outbreak scenario is unique and requires a bit of explanation.
For the majority, BT maize kept the fall army worms at bay in many fields. However, Rice said the acreage of non-GMO corn planted across the country is increasing. In states like Kansas, where there are more non-GMO corn varieties, he noted that they “get hammered pretty heavily” by FAW.
He said farmers switching to non-GMO crops need to look out for this native pest more often. Likewise, those with pasture and forage land should look out for Fall Armyworms, as much of the impact of 2021 in Missouri has been on those acres.
The exact level of return of farmed army worms in 2022 is still unknown. “They didn’t leave,” Rice noted. “They are still there.”
The Role of Weather in Survival
Fall Armyworms overwinter in the lower reaches of Florida and Texas. Rice said these are the two places where populations can survive the winter in the United States, as adults and larvae only die when it’s below 50 degrees F. Simply, the fall armyworms are not cold hardy. Thus, this small population winters in these warmer southern states.
However, warm, mild winters across the country are causing more Fall Armyworms to survive in more northern states. “When you have warmer winters, like we’re experiencing right now, populations will survive in Mississippi, Alabama and Georgia and maybe even farther north,” Rice warned.
This year’s warm winter and more northerly populations increase the chances of survival for the Fall Armyworm, which increases the population as the 2022 growing season approaches.
These surviving populations will spread, but not evenly.
Every spring and summer, Fall Armyworms re-invade the entire North American continent. When the FAW emerge, the moths come out of the ground, circle upwards and catch the jet stream, Rice explained.
From there, these parasites act more like a parachutist, falling from the sky. The only difference is that there is no designated drop zone. Everything is random for the fall armyworm. “That’s why it’s hard to predict where they’re going to be,” Rice said. “That’s why your neighbor might have fall armyworm problems and you don’t. It is the unequal distribution.
Last year, wild distribution reported fall armyworm damage as far east as Virginia, a state where these caterpillars aren’t usually a major pest.
Another problem that entomologists like Rice face in controlling FAW is insecticide resistance.
“We had many populations that were resistant to pyrethroids,” Rice explained. It was first reported in the Gulf States, but Missouri has also found a few populations that have shown some resistance.
Rice said that due to the migration pattern of flying thousands of miles, a resistant population in southwestern Missouri could spread these genes across the state “pretty quickly.”
“I suggest you stop using pyrethroids for FAW,” he said. “It’s a real big bet.” Rice said there are other chemical options that work well at different life stages.
Due to the large outbreak of fall army worms last year and the possibility of a repeat this year, Rice said farmers should contact their chemical sales representative to reserve the product now.
Fall armyworms are a global problem, spreading to Africa in 2016 and then to Asia.
Due to the range of this pest with limited control options, entomologist Kevin Rice of the University of Missouri Extension received funding to research ways to kill the army worm at field edges before it destroys the whole harvest.
Her MU research lab studies pheromone attractants to lure women into a suicide trap. “We want to kill the female insects because they are the ones that multiply and lay eggs,” Rice said. “We’re seeing if we can basically find a plant follicle that attracts females.”
UM graduate students working on the project release army worms in a wind tunnel and release attractants. Then, using an olfactometer, they test the female’s attraction or preference for different chemicals. Rice’s lab is also trying to identify a larval-stage attractant.
“We know that the larvae, when they come through these fields, smell a host plant,” Rice explained, “and what we hope is that if we can identify any of these chemicals that they follow , we could build a pit with a suicide trap.
The trap would be like a bucket with the identified chemical attractant on top. When the army worm reaches the top, it falls and kills itself.
Rice said her lab is also considering using pheromones to confuse moths before they lay eggs. This method would prove beneficial for non-GMO crops and pastures in the United States