Unspoken Truth About Pests: This Pest Can Cost You 15% to 50% in Yield Loss

In the 40 years Gus Lorenz has focused on pests, 2021 marks a first.

“This fall armyworm outbreak is the worst I’ve seen in my career,” says Lorenz, Extension entomologist for the University of Arkansas System Division of Agriculture. “It's not just rice, it's really bad in soybeans. We see a few in cotton, and they're in grain sorghum and even eating corn.”

Lorenz says the fall armyworm infestation is widespread, not just by crop type, but also by geography this growing season.

“It's from one end of the state to the other, it’s all four directions. It's bad everywhere," he adds. “And in the pastures, we've had several fields where the hay crop was totally devastated by it.”

As Arkansas farmers and entomologists work to battle the pest, Lorenz says this year has been the “perfect storm” in the worst way. Torrential rains in May and June caused flooded fields, and as farmers were forced to replant late that caused another problem to sprout early.

“They don't call it fall armyworm for nothing,” says Lorenz. “It usually strikes us late, but this year it started early. I've never seen so many fall armyworms. Anywhere you go, everybody's got fall armyworms.”

It's a problem so potent this year, farmers don’t have to walk or drive far to see it.

“A lot of times you can see them from, you know, the truck driving down the road, especially in some really bad situations,” says Ben Thrash, Extension entomologist for the University of Arkansas System Division of Agriculture. “In soybean fields, they just leave stems out there in the field, so it's kind of easy to spot out there.”

Yield-Robbing Pest 

Once the worms grow to an inch long, the fall armyworm damage can be devastating, especially in rice.

“We can tell you based on work the university has done, that once you start seeing around 20% defoliation, it can cost you anywhere from 15% even up to 50% yield loss,” says Lorenz.

What can be more detrimental is how the pest delays crop maturity.

“If they eat the crop down and it has to grow back, it can delay maturity by up to 30 days, and that's the difference in making a crop a lot of times and not,” Lorenz says.

It’s not just rice facing crop loss from fall armyworm infestations. Soybeans are also seeing the surge, which can cause crop-loss costs to add up quickly, too.

“In soybeans, and in the vegetative stage of soybeans, a lot of times on late-planted crops it can range up to about 30% to 35% yield loss from defoliation on those small soybeans,” says Thrash. “Now you get later on in the growing season in reproductive soybeans, and it can be a lot higher than even that.”

“The impact is much greater on late-planted stuff than it is with earlier planted crops, because it doesn't have time to compensate for that defoliation,” Lorenz adds. “When you have late-planted crops, and you get these kind of insect infestations, it's doubling down on the impact to our growers.”

Weed Pressure's Impact on Pest Pressure 

Thrash says the other issue in soybeans this year is an increase in weed pressure. The weeds are attracting the pests, but once the weeds are managed by the grower, it may be too late to rid the fields of the pests, as well.

"We had all this weather, which delayed a lot of our herbicide applications. And so grass got to grow up in some of these soybean fields,” says Thrash. “As the fall armyworms prefer the grass out there in the field, whenever it finally dries up enough to where the grower can make a herbicide application, he kills the grass while the armyworms on the grass are still out there in the field. So, they move off on the soybeans, and a lot of times those worms are already pretty good size. And that's when they do 90% of what they're going to eat in their whole lifetime in those last couple growing stages."

Sent by one of our consultants from grass between rows. Armyworm’s are worse this year than anyone can remember. pic.twitter.com/JrPiDrqogp — Angus Catchot (@acatchot) July 30, 2021

Coming for the Midwest? 

As farmers in Arkansas battle an army of armyworms, it’s an issue Lorenz warns could be coming for the Midwest next.

“I think the folks up in the Midwest, and northern Missouri and up in Indiana and Illinois, I think they'll all get a little taste of this fall armyworm before it's over with,” says Lorenz.

True Cost of Pest Pressure

Farm Journal Field Agronomist Ken Ferrie says the true cost of pest pressure varies by the insect.

“We've seen corn borer pressures that amount to a 30-bushel or 40-bushel per acre loss, and when we talk about corn rootworm, it depends on whether the rootworm pressure is heavy enough and the corn goes down. If the corn is still standing, it might be a 7- to 10-bushel loss. But if corn goes down, it can be 30 to 40 bushels in yield loss.”

Ferrie warns the cost of pest pressure doesn’t always come from yield.

“For instance, the issue of down corn, whether that be a rootworm issue or maybe some corn borer issue, it slows down the harvest,” says Ferrie. “So, not only would it take away yields, it may double the amount of time in harvesting and the situation where that cost in the fall can be pretty expensive, especially if you're up against the weather to get all your fall work done.”

As the cost of pest pressure can add up quickly in the fall, Farm Journal Associate Field Agronomist Missy Bauer says timeliness of application is key.

“If you go out here and you're too late, you've already had too much damage, and we've given up too much yield,” she says.

Bauer cautions it’s not just timeliness with scouting, but also treatment.

“If you start to realize that you have some clipping issues going on in your corn tassel, and you have nobody even lined up to potentially help you spray and take care of that, whether it's an airplane or a ground rig, it’s too late,” she says. “So, you should always have your plan laid out. And then, as you see issues, you just have to implement the plan that's laid out there. If you missed the boat on the timing side of it, we're behind the eight ball, we're giving up a lot of yield in a hurry.”

Below-Ground Problems

And the lurking insects aren’t just above ground, but below what the eye can see.

“They're feeding on those corn roots when you can't see what's going on,” Bauer says. “So, unless you're digging up the plants and doing some rootworm floats, you really have no idea what that pressure is like until they actually hatch. And now you've got beetles clipping on the silks instead. So, it’s things below ground that I think we've got to be cautious of.”

High Pest Pressure Overall

For farmers in the South, the growing concern about pests this year isn't just with fall armyworms but also with plant bugs.

“We're looking at maybe seven, eight, even nine applications to control this plant bug situation in cotton for a lot of our growers,” says Lorenz.

As the quest to protect valuable bushels and pounds in fields continues, Lorenz reminds growers that every detail counts.

“Maintaining the area around the field and keeping those turn rows where they're not producing seed heads can have a huge impact,” he says.

The Extension entomologists say there are production practices a grower can implement to help with insects. The first is plant early. The other is try to plant in narrow rows to allow for faster, greater canopy. And when it comes to cotton, make sure cotton fields aren’t planted next to corn. However, both Lorenz and Thrash say weather has the final say every year, and wet weather this year meant some of those options were not possible or feasible.

Read more about the Unspoken Truth About Pests.