As Southern Farmers Fight Fall Armyworm Damage, EPA Grants Insecticide Relief in Rice

As grasshoppers invade drought-stricken fields in North Dakota and Montana, in the South, heavy rains and flooding in late May and early June are causing a different issue, an army of fall armyworms that are demolishing crops. 

“I've been looking at crops and doing this bug thing for well over 40 years, and I can tell you right now that this fall, armyworm outbreak is the worst I've seen in my career,” says Gus  Lorenz, Extension entomologist for the University of Arkansas System Division of Agriculture.

Fall armyworms are taking over fields, hitting everything from soybeans to rice. But until this week, growers in the nation's leading rice-producing state only had one insecticide approved for use on fall armyworms in rice - pyrethroid - and Lorenz says they are growing resistant to it. 

“Insecticides we use labeled in rice -the pyrethroids - if you're only getting 50% control or less that's still not killing enough worms to get the population under control, and that’s what’s needed to stop your defoliation out there,” says  Ben Thrash, Extension entomologist for the University of Arkansas System Division of Agriculture.

EPA grants crisis exemption to help #Arkansas #rice farmers fight #armyworm scourge.https://t.co/mYa9yHgV5X pic.twitter.com/aSsq2ucfnh — UA System Div of Ag (@AginArk) July 28, 2021

That's why University of Arkansas System Division of Agriculture filed documentation with EPA on July 23 to obtain a Section 18 exemption to use Intrepid on rice. Not even a week later, EPA granted a crisis exemption, allowing Arkansas farmers to use Intrepid on their rice fields. The crisis exemption allowed farmers in the state to use Intrepid beginning July 28.

“These larvae can cause a lot of damage because there's so many of them,” says Lorenz. “It’s not uncommon for us to go out and make just one sweep through rice or soybeans and have 20 or 30 armyworms. And with those kind of numbers, it can cause a lot of damage in a short amount of time.”

Battling Fall Armyworms Across the South 

Entomologists say the outbreak has already cost growers millions of dollars in losses, not just in Arkansas, but across the South.

According to the latest Midsouth AgFax newsletter, fall armyworms are moving north with reports coming in from Louisiana to Tennessee. And even in crops where other insecticides are approved for use, insecticides are sometimes hard to find. And now, entomologists in other states are also asking EPA for emergency approval to use Intrepid on rice.  

“My research counterpart, Dr. Tyler Towels, and I have submitted our Section 18 request for using Intrepid in rice for fall armyworm control to the Louisiana Department of Agriculture and Forestry. We are just waiting on a decision from the regulators. Hopefully we will hear something within the next week,” says Sebe Brown, Louisiana Extension field crops entomologist: 

As entomologists are discovering, the later-planted crops are more at risk for a fall armyworm infestation. And as heavy rains blanked the South late spring, late-planted crops in the South became common this year.

“Insects are more of a concern in a late-planted crop," says Ty Edwards, Edwards Ag Consulting, LLC, Water Valley, Miss. "It gives pests longer to build in the environment, and the plants are more at risk later in the season. Corn and soybeans are mostly on time, but cotton is the one we’re watching closest. In previous years, we would be looking at cotton at cutout next week (from July 27). There’s very little of that around, and I think we will be managing most cotton fields through the end of August. "

Pasture/Hay Fields at Risk 

From Mississippi to Tennessee, farmers are battling armyworms, and it's often pastures and lawns attracting pest, which is causing widespread damage in areas.

“Like everyone else, we are fighting fall armyworm infestations,” says Scott Stewart, director of West Tennessee AgResearch and Education Center, Jackson, Tenn. “I’m expecting them to stick around for a while in pasture grasses, in particular. They love bermudagrass, and they’re even jumping on lawns right now. They are not in every field, but 2021 will be remembered. They have been an issue in our later-planted soybeans most of which are double-cropped after wheat. We’ve seen everything from mild to catastrophic infestations where they caused 100% defoliation of pastures and late-planted soybeans. They are showing up in late-planted milo, corn, sweet sorghum and sorghum sudangrass, really everywhere except cotton so far."

Mississippi farmers are also watching the pest spread from hay fields to cotton fields, which is another issue in battling the pest this year. If a farmer or producer cuts a hay field or mows down ditches, it often takes away the host plant where the armyworms were feeding.

“We found fall armyworms  crawling out of a cut pasture today (July 27) and into several cotton fields,” says Edwards. “The fall armyworms were climbing the stalk and knocking off leaves, squares and small bolls. This was Bollgard II cotton and was treated immediately with Diamond, and the fruit retention looks really good. “

Short on Supplies

Stewart says the issue in his area  is finding the right insecticide to apply. Not only is it an issue of what insecticide you can apply on certain crops, but there's also struggles in finding supplies. 

“We’re struggling to choose when and what insecticides to apply for fall armyworm,” he says. “We’re running short of the chemistries we have the most confidence in because so many areas are spraying for them across the Midsouth. Normally the strain we get in pastures and soybeans this time of year is the grass-strain, which is generally pretty easy to control with pyrethroid insecticides, though re-infestations may occur.  This year, control has been hit or miss with pyrethroids. We’re trying to avoid running straight pyrethroids, but they are working OK in some cases. “

Edwards says the biggest concern he has is with the soybeans. A combination of insecticides seems to be providing some control, but often times that insect control doesn’t prove to be 100%.

“Usually fall armyworms are associated with grass/Roundup applications, but this year I believe they’re targeting the beans,” says Edwards. “The timelines don’t add up with how long the grass has been dead versus how young the larvae are. I’ve tried about every combination out there. Of course, Prevathon and Besiege have performed the best, but they’re the most expensive option as well. Pyrethroid plus Diamond showed 90% to 95% control today (July 27) over a substantial number of acres treated over the weekend, so I expect that number to get better with time. Seven days from treatment, Pyrethroid plus 3 ounces of Dimilin provided 100% control, but this was applied to three- to five-day old larvae. Pyrethroid alone was giving 50% to 60% control earlier in the season."

Entomologists say fall armyworm is also hitting earlier than normal. As the name suggests, the pest is typically a fall issue. This year, the infestations are happening quicker and much worse than in previous years.