Root Out Rootworms

Long-term strategies to manage resistance in corn rootworm is key to preserving valuable technologies.
Root Out Rootworms
In York, Nebraska, a hybrid with Agrisure Duracade (left) has a healthy root system, while a hybrid without Agrisure Duracade (right) has weakened roots.
Humans domesticated modern corn over thousands of years from an ancient grass called teosinte. But it took only a fraction of that time for corn rootworm (CRW) to adapt to several typical pest management practices. Given that CRW costs growers around $1 billion in lost yield and control measures each year, finding a way to manage it is crucial. While there’s no one-size-fits-all solution, there are steps growers can take to plan strategically for long-term CRW management.

Long-term strategies are key to managing resistance in #cornrootworm.

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“They’ve overcome almost everything that growers have tried to throw at them: crop rotation, different types of corn genetics, insecticides and transgenics,” says Erin Hodgson, Ph.D., associate professor and extension entomologist at Iowa State University. “They’re just a really adaptable pest.”

Fighting Adaptations

Hodgson and most experts agree that crop rotation is still the single most effective way to control CRW. The practice works by starvation. The only mobile form of the insect is the adult beetle. After the adult beetles lay eggs in a cornfield, the grower can rotate to soybeans or other crops the following year to starve the larvae and end the cycle.

“You’ve got to consider all the tools in the toolbox and try to use those tools to expose CRW to something different through a multiyear field-by-field plan.”

Tim O’Brien
This practice works for most of the Corn Belt; however, two species have adapted to this strategy. Beginning in the 1990s in areas of the Eastern Corn Belt within Illinois and Indiana, the western CRW variant females began to lay their eggs in soybean fields, reducing the benefits of rotation. This variant of the Western corn rootworm has now crossed into neighboring states, so growers are advised to monitor its movement and consult with their local Syngenta resellers on appropriate control practices. Areas of the Northern Corn Belt face extended diapause, where eggs of the northern CRW can stay dormant in soil for two or more years, waiting for corn to be planted in the field again.

These examples and other adaptations that make corn rootworm more difficult to manage are the reasons why many experts, including Syngenta Traits Product Manager Tim O’Brien, say that a long-term, multifaceted strategy is the best way to deal with the billion-dollar pest.

“The larvae feed on the roots, damaging their ability to uptake water and nutrients,” O’Brien explains. “This places stress on the plants and leads to yield reductions. Damage to brace roots can lead to standability concerns, making plants susceptible to lodging. Come harvest, growers find it really stressful and difficult to get lodged corn to feed into a combine.”

A Novel Trait

When crop rotation isn’t an effective option for CRW control and growers need to consider other management strategies, using Bacillus thuringiensis (Bt) traits for CRW can be an excellent option. Bt is a soilborne bacteria that produces proteins affecting digestion in the gut of specific insects. Researchers first documented the activity that these proteins have on larvae in the early 1900s. For nearly 100 years, growers have used the proteins to control insects—with the introduction of the first transgenic traits developed from Bt for insect control taking place during the 1990s.

In the two decades since, Syngenta scientists have continued to refine the technology. One of the newer tools from Syngenta that can help tackle CRW is a Bt trait called Agrisure Duracade®.

“It’s a unique mode of action versus competitive traits in the marketplace,” says Todd McRoberts, NK® agronomy manager at Syngenta. “It’s a novel protein, engineered in the lab, which attacks a different site in the stomach of the rootworm.”

Agrisure Duracade offers a new tool against CRW larvae. The Agrisure Duracade trait expresses a protein that binds differently in the gut of CRW than any other trait on the market. Additionally, it is always pyramided with a second mode of action against CRW and provides effective control of western, northern and Mexican CRW.

A unique trait product, like Agrisure Duracade, provides an ideal foundation for a CRW control plan. However, O’Brien suggests that all operations should use a range of technologies and strategies to combat the pest.

“The one thing you don’t want to do is keep using the same thing in the same field year after year,” he says. “You’ve got to consider all the tools in the toolbox and try to use those tools to expose CRW to something different through a multiyear, field-by-field plan.”

In addition to crop rotation and different transgenic traits, traditional insecticides, including the Force® family of insecticides, are tools that growers should continue to consider.

“When growers pair Agrisure Duracade with some of our other insect control technologies, like Force, the Agrisure Viptera® trait and our insecticide seed treatments, they can achieve the broadest spectrum of insect control in the industry,” O’Brien says.

For example, trait stacks featuring Agrisure Viptera offer cutting-edge control of aboveground insects, including western bean cutworm and corn earworm. Avicta® Complete Corn 250 and Avicta Complete Corn 500 seed treatments defend against a wide array of damaging nematodes and seedling pests.

Staying a Step Ahead

McRoberts and O’Brien both suggest building out a long-term program to take on CRW. By sitting down with their resellers, growers can take the issues specific to their fields and lay out a plan for this year and the next several years. The plan may need to change each season, depending on pressure, but having it in place gives growers a head start. And when it comes to keeping programs effective, there’s no substitute for good scouting.

“The single most effective thing I recommend for all growers, no matter what strategies they’re using, is to assess their crops at the roots,” Hodgson says. “It’s not fun to scout and dig up roots in July, but the best way to make sure your program is working is to get out there and check.”

For more information on developing a field-by-field corn rootworm management plan, please refer to the “Take Control of Corn Rootworm” decision guide.