Entomologists seek emergency-use exemption to help rice growers in ‘epic’ battle against armyworms
Armyworms threaten rice, entomologists seek Section 18 exemption for insecticide
July 21, 2021
By Mary Hightower
U of A System Division of Agriculture
- Lorenz: Armyworm situation is ‘epic’
- Intrepid used in similar situation in California
(Newsrooms — with art: sweep net with worms https://flic.kr/p/2mcweex, Armyworms in flooded rice: https://flic.kr/p/2mcDFT2, entomologist examining rice field https://flic.kr/p/2mcB31X)
LONOKE, Ark. — University of Arkansas System Division of Agriculture entomologists are seeking an emergency exemption to allow for the use of Intrepid to help control armyworms that threaten the state’s 1.24 million acres of rice.
“This is the biggest outbreak of fall armyworm situation that I’ve ever seen in my career,” Gus Lorenz, extension entomologist for the Division of Agriculture, said Wednesday. “They’re in pastures, rice, soybeans, grain sorghum. It’s epic.”
Lorenz said the Section 18 request to enable use of Intrepid should be submitted to the Arkansas State Plant Board by Friday.
Intrepid is a growth regulator that’s approved for use in just about every other row
crop but is not labeled for use in rice.
“This armyworm thing started about three to four weeks ago,” he said. “It’s continued to build from that time. It’s from the Bootheel of Missouri down to Louisiana.”
Lorenz said he received a call from a producer in “south Arkansas, that they’d eaten his bermudagrass pasture to the ground. It was a 30- to 40-acre pasture. And he wasn’t even calling about the pasture. He was calling about his rice crop. He said his rice was being eaten to the ground.”
“Fall armyworm is a particularly voracious caterpillar,” said Jarrod Hardke, extension rice agronomist for the Division of Agriculture. “They have a tendency to surprise us because adults lay very large egg masses but the earliest instar larvae eat very little. It’s not until they get older and start to spread out that they consume most of the food in their life cycle.
“This is why we go from zero to TREAT seemingly overnight,” Hardke said.
Why a Section 18?
Typically, armyworms can be managed well using pyrethroids, but Lorenz said “when this outbreak first started, we got reports out of Texas and Louisiana that they weren’t getting control. We’re getting failures.”
Lorenz said he and colleagues ran some quick tests, spraying this year’s armyworms with pyrethroids “and we got 48 percent control.”
In cattle-heavy parts of the state producers use another insect growth regulator called Dimilin to manage armyworms, but in row crop country, “they just don’t carry it. It’s just not available,” Lorenz said.
Fellow extension entomologist Nick Bateman said, “another problem with using Dimilin is the pre-harvest interval. The pre-harvest interval on Dimilin is 80 days which will lead to major harvest issues.”
“We’re limited on the options in control for rice,” he said. “It’s not just a problem of row rice. We are also seeing them in flooded rice, all through the field. They are eating rice all the way down to the waterline.”
Lorenz said rice growers in California sought and received a Section 18 exemptions over the last three years. “We felt like that was our best option.”
Arkansas farmers who managed to replant after the floods and heavy rain in June have young, tender plants that are highly attractive to armyworms.
“Those crops are extremely susceptible to damage from armyworms,” Lorenz said.
“My concern is that if we get another generation of them, the next wave could be unbelievable,” he said.
The first generation of armyworms matured into moths in Texas and Louisiana and flew northward. Now that they’re in Arkansas, “We’re making our own generation, which is what makes it so dangerous,” Lorenz said.
There’s also a chance that, depending on the environment, “the population could collapse,” he said. “There are some natural controls out there. When you get a big buildup a lot of things can happen. There are a lot of naturally occurring pathogens that can help control them.”
Some agents in southwest Arkansas found armyworms that had fallen victim to a naturally occurring virus. Lorenz is hoping that virus may provide another option for control in the future.
Arkansas is the nation's leading rice producer.
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To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit www.uaex.uada.edu. Follow us on Twitter and Instagram at @AR_Extension. To learn more about Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website: https://aaes.uark.edu. Follow on Twitter at @ArkAgResearch. To learn more about the Division of Agriculture, visit https://uada.edu/. Follow us on Twitter at @AgInArk.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
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Media contact: Mary Hightower