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How to defend your farm against corn rootworm

A hidden monster lurks under the soil, destroying corn crops and farmers’ bottom lines.

Midwest flooding may have significantly lowered populations in 2015, but expansive testing and farmer surveys show corn rootworm is on the rise.

“We’ve started to see somewhat of a population increase, especially in the last two years in certain geographies, based on survey data we’ve done internally as a company,” says Preston Schrader, Bayer Crop Science seed and trait technology development representative.

Lack of significant weather events and a rising number of farmers committing to corn-on-corn acres may have led to the population growth.

“As economics shift, we have had a higher demand for corn on corn,” says Bruce Battles, Syngenta technical agronomy manager. “We see a higher number of growers committing to at least two to three years of growing corn before rotating back to soybeans. As you do that, you start to build up populations.”

Heavily relying on seemingly simple fixes may also factor into the pest’s rise.

“It’s human nature to want a simple solution,” Battles says. “It’s no different than what we’ve seen in other areas of agriculture, like weed control. You find a new tool, it gets broad-scale adoption, then you start seeing resistant weeds. In some pockets, we’re seeing similar things due to a heavy reliance on a singular approach like pyramided traits [several traits stacked on each other]. Over time, that catches up with you, and I think we’re facing the outcome of some of those years of simplicity.”

Data Saves

Continually collecting data in fields is a farmer’s top defense against corn rootworm.

“From a core rootworm pressure standpoint, knowing and understanding the problem at hand is the key,” says Travis Coffman, Bayer Crop Science traits marketing manager for corn and regional crops. “Then there are a lot of solutions or practices you can implement.”

With no rescue treatments available, farmers should diligently plan for rootworm pressure before the growing season begins.

Eggs that rootworms lay in the summer and fall don’t normally hatch until the following year. “Unfortunately, those eggs are below ground, so there are very few economical options to control those insects as soon as they hatch,” Schrader says. “That’s why from a protection standpoint, you really need to think before you drop the seed in the ground about how you’ll protect against rootworm.”

Data from previous growing seasons can help farmers determine their risk for rootworm damage.

“Look at the current year and make decisions off of that,” Battles says. “I strongly encourage people to build a plan for 2023. Learn as much as you can in this year to build that 2023 plan out because the best way to learn is getting out in the field.”

Routine root digging can help quantify the amount of damage a farmer faces.


“That’s the first way to identify if you have pressure there,” Coffman says. “If you do have pressure, those roots would be rated on something like the Iowa State 0 to 3 scale [0 is no damage, 3 is severe]. That’s a way to economically identify the potential damage that you’re going to have from a yield perspective.”

Farmers may also place sticky traps in fields to understand the population pressure and make better management decisions.

“Traps are a really good indicator of which fields are going be at a higher risk in 2023,” Battles says. Fields that are particularly high risk could benefit from a beetle spraying program, a practice that can reduce eggs but one that also requires a timely application.

Managing Rootworm

Whenever possible, rotating with soybeans is one of the most effective ways to manage corn rootworm.

“Soybeans are a nonhost crop, which means rootworm can’t survive on soybeans,” Schrader says. “When you rotate to a soybean, the beetles have no ability to hatch the next year because they rely on corn roots to live. That’s why a corn rotation works so well.”

Some rotation-resistant corn rootworms have been spotted, but the risk for corn-oncorn production remains much higher.

“Situations where you find corn on corn are where you really need to consider the traits you’re using for your farm program because you want to make sure you do adequately control those core rootworms,” Schrader says.

Working with local agronomists and other experts, in addition to utilizing pyramided products, can help farmers create a plan.

RNAi Technology

Bayer recently introduced SmartStax PRO with RNAi technology, offering farmers a new tool for dealing with corn rootworm pressure.

“This pest has such a high likelihood and high ability to adapt to any technology we develop,” Schrader says. “We’re always trying to develop new modes of action to control this pest and stay one step ahead.”

While previous products have focused on multiple BT proteins, RNAi technology is able to pinpoint specific proteins corn rootworms need to survive.

“We’ve got limited volumes in 2022 that we’re talking to farmers about now, and in 2023, we plan on expanding that pretty heavily,” Coffman says. “Last year in particular, we found that it’s going be the strongest biotech defense against corn rootworm compared with all the other competitors in the marketplace.”

With three modes of action in one product, SmartStax PRO with RNAi technology offers an opportunity to extend the life of existing management options. It’s an exciting development, but Battles warns farmers to stay cautious.

“If we come into it with the mind-set that RNAi is the thing that will take care of rootworms, and it becomes our only management strategy toward it, resistance is just a matter of time,” Battles says. “It’s a matter of how many years it takes for that new technology to become obsolete. There are a lot of good technologies coming through the pipelines, but I just encourage people not to look at that as the singular new approach to managing the problem. It doesn’t replace the need for a multipronged approach to management.”

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