Reports of the fall armyworm date back to the 1700s. At that time, U.S. newspapers were reporting widespread outbreaks as these pests aptly lived up to their namesake — marching across fields by the hundreds of thousands, devouring plants and leaving devastation in their wake.
In 2021, the pest once again showed its might, reaching the largest population in 30 years and stretching across the U.S. from the Southeast and Northeast into the Midwest.
“It’s an outbreak pest,” University of Missouri Extension entomologist Kevin Rice said during the MU Crop Management Conference. He said farmers should expect an influx in armyworms every 30 to 50 years. Given that timetable and the severity of armyworm pressure in 2021, many crop and livestock farmers are wondering if there will be a repeat in 2022.
Rice said the scenario for fall armyworm outbreaks is unique and takes a bit of explaining.
For the most part, Bt corn kept fall armyworms at bay in many fields. However, Rice said non-GMO corn acres planted across the country are on the rise. In states such as Kansas with more non-GMO corn varieties, he noted “they are getting hammered pretty heavily” with fall armyworms.
He said farmers switching to non-GMO crops need to scout more often for this native pest. Likewise, those with pasture and forage ground need to scout for fall armyworms as much of the 2021 impact in Missouri was on those acres.
Just what level farm armyworms return in 2022 is still unknown. “They didn’t go away,” Rice noted. “They’re still here.”
Weather’s role in survival
Fall armyworms overwinter at the very bottom tips of Florida and Texas. Rice said these are the two places that populations can survive the winter in the U.S. because the adults and larvae only die when it’s below 50 degrees F. Simply, fall armyworms are not cold hardy. So, this small population rides out the winter in these hotter Southern states.
However, the 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, you’re going to have populations survive in Mississippi and Alabama and Georgia and maybe even farther north,” Rice warned.
This year’s warm winter and more northern populations increase the chance of fall armyworm survival, which increases the population going into the 2022 growing season.
These surviving populations will spread, but not evenly.
Every spring and summer, fall armyworms reinvade the entire North American continent. When fall armyworms emerge, the moths come out of the soil, fly in a circular pattern straight up and catch the jet stream, Rice explained.
From there, these pests act more like a paratrooper, dropping out of the sky. The only difference is there is no designated drop zone. It is all 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 issues and you don't. That's the patchy distribution.”
The wild distribution last year had fall armyworm damage reported as far east as Virginia, a state where these caterpillars are not typically a major pest.
Another issue entomologists like Rice face in controlling fall armyworms is insecticide resistance.
“We had numerous populations that were reported resistant to pyrethroids,” Rice explained. It was first reported in the Gulf states, but then Missouri also found a couple populations that showed some resistance.
Rice said because of the migration pattern of flying thousands of miles, a resistant population in southwest Missouri may spread those genes across the state “pretty quickly.”
“I'm suggesting that you no longer use pyrethroids for fall armyworm,” he said. “It's a real big gamble.” Rice said there are other chemical options that work well at different life stages.
Due to the large outbreak of fall armyworms last year and the potential for a repeat this year, Rice said farmers should be contacting their chemical sales representative to reserve product now.
Fall armyworm research on the way
Fall armyworms are a worldwide problem, spreading to Africa in 2016 then on to Asia.
Because of the reach of this pest with limited control options, University of Missouri Extension entomologist Kevin Rice received funding to look for ways to kill the armyworm at field edges before it destroys the entire crop.
His MU research lab is studying pheromone attractants to lure females into a suicide trap. “We want to kill female insects because they're the ones multiplying and laying eggs,” Rice said. “We're seeing if we can find basically a plant follicle that the females are attracted to.”
MU graduate students working on the project are releasing the armyworms into a wind tunnel and release attractants. Then using an olfactometer, they test the female’s attraction or preference to different chemicals. Rice’s lab is also trying to identify an attractant at the larva stage.
“We know larva, as they march across those fields, are smelling for a host plant,” Rice explained, “and what we're hoping is that if we can identify one of those chemicals that they're tracking, we could build a pit with a suicide trap.”
The trap would be like a bucket with the identified chemical attractant on the top. As the armyworm reaches the top, they fall in and kill themselves.
Rice said his lab is also looking at using pheromones to confuse moths before laying eggs. This method would prove beneficial for non-GMO crops and pasture in the U.S.