Strange, disc-shaped damage appeared in several of Jeff Ruff's cornfields. It looked like “deer had twisted it up,” guessed the southwestern Minnesota farmer, who consistently rotates corn with soybeans.

Yet, a more careful look clearly showed corn rootworm feeding had severely damaged roots and caused stalks to topple. It was Ruff's first inkling that he might need to do more to control corn rootworms than simply rotate his crops.

Corn rootworm has infested about 30 million acres across the Corn Belt, says Todd DeGooyer, corn insects technology manager for Monsanto. Rootworm infestations are typically a problem on corn planted after corn, he says. But trouble spots for rootworm infestations are becoming increasingly more common on corn following soybeans.

In parts of southwestern Minnesota, northwestern Iowa and southeastern South Dakota, northern corn rootworm beetles have begun to delay their egg hatch for two years, anticipating the traditional soybean/corn rotation.

Other trouble spots with rootworm feeding on corn following soybeans occur throughout eastern Illinois, Indiana, southern Wisconsin, southern Michigan and western Ohio. In these regions, western corn rootworms are laying eggs in soybeans, oat stubble and alfalfa prior to rotations back into corn.

DeGooyer says Monsanto's new YieldGard Rootworm hybrid is a good option for farmers who want to avoid handling insecticide, no matter what their crop rotation, if they're concerned about rootworm damage. The new rootworm-resistant technology is genetically modified to contain a protein (Bacillus thuringiensis) toxic to corn rootworms that feed on roots.

Ruff considered a soil insecticide application on his entire corn acreage this past growing season. Yet, he didn't want to incur the expense of adding granular insecticide boxes to his corn planter to fix a problem he wasn't sure was costing him much economic harm. “The problem is, some fields have it and some fields don't,” he explains.

Another deterrent for Ruff was the idea of handling an insecticide at planting. “Insecticides are probably the most dangerous crop protection product a farmer can use,” he says. “I may have to use an insecticide eventually, but I'd love not to have to bother with it.”

Ruff decided to try Monsanto's YieldGard Rootworm corn. Due to late EPA approval and limited supply, he was able to plant only 12 bags of Dekalb DKC46-23, a rootworm-resistant corn, that covered about 26.5 acres on a 160-acre field. In the past, he had split this field equally between corn and soybeans, but now he wanted to plant it to just one crop: corn this year and soybeans the next.

The results were eye-popping. Rootworm-resistant corn stood well and yielded 157 bu./acre when averaged among three different yield checks. Considering the lack of moisture the area had experienced during much of the growing season, Ruff was impressed. A similar Dekalb hybrid, DK51-43, without the YieldGard Rootworm technology, averaged only 88 bu./acre. Both hybrids were planted on ground previously planted to corn.

“This field would have been a disaster if I hadn't had the new genetics,” says Ruff. “I'm looking forward to planting more of it, especially when it's stacked with corn borer resistance. Every year, we plant about a third of our corn to corn borer-resistant hybrids — it's kind of a gamble not to plant it in this area.”

Western Nebraska farmer Tom Terryberry, who also planted Dekalb rootworm-resistant corn in 2003, agrees. “When they stack corn borer and corn rootworm resistance together, we'll look to expand acres with it,” he says. “It was good corn, but had it been corn borer resistant as well, it would have added another 10-15 bu. onto the yield.”

Terryberry planted 75 bags of DKC53-29 and DKC60-12 rootworm-resistant corn on irrigated, continuous cornfields. The hybrids yielded well, between 220 and 230 bu./acre, but not as well as his Pioneer 34H31 (a conventional hybrid) and 34B98 (a Bt corn borer-resistant hybrid). Neither of these two hybrids contained biotech corn rootworm-resistant genetics. The irrigated Pioneer hybrids yielded between 235 and 240 bu./acre on ground also previously planted to corn.

Terryberry controlled rootworm feeding on his Pioneer hybrids with Capture insecticide, a liquid applicator and a Raven monitor.

“You could tell that the rootworm-resistant seed provided a healthier-looking root,” he says. “Now it's just a matter of getting the technology into the best hybrids that work on our ground.”

Further east, Mike Gray, University of Illinois extension entomologist, says YieldGard Rootworm hybrids have been performing well in root trials at several locations across the state.

“Dekalb YieldGard Rootworm hybrids had very low rootworm damage even when pressure was well above economic injury levels,” says Gray. “YieldGard Rootworm not only was competitive, but in most cases crop injury was less than with conventional soil insecticide and seed treatments.”

In northeastern Iowa, Duaine Davis, who farms near Luana, says he had good results planting 12 bags of Dekalb DKC53-29 rootworm-resistant corn this year. The rootworm-resistant hybrid averaged 198 bu./acre, yielding 30 bu./acre more than its sister hybrid, Dekalb DK53-34. This second hybrid lacked the rootworm-resistance trait, but was planted with Force insecticide at planting. Both hybrids were planted on corn following corn.

Gray says several factors may cause soil insecticides to become ineffective, such as soil conditions that are either too wet or too dry, cool spring weather that delays rootworm larval hatch (extending the larval feeding period), early planting and uncalibrated equipment. He adds that the YieldGard Rootworm technology provides root protection all season long; insecticide protection may be more limited in duration — depending upon environmental conditions and planting dates.

In western Minnesota, Mark Pankonin says costs were comparable between YieldGard Rootworm corn (Dekalb DKC53-29) and its non-resistant sister hybrid (Dekalb DK537), which he banded with Counter CR soil insecticide at planting. However, the rootworm-resistant corn averaged 173.4 bu./acre, or 1.5 bu./acre better than the conventional corn. He also planted a check plot of the same non-resistant hybrid with no insecticide at planting. This plot yielded 140.9 bu./acre, or almost 33 bu./acre less than the corn rootworm-resistant hybrid.

Although Pankonin planted these particular hybrids to corn following corn, he's also seen considerable lodging due to corn rootworm on corn following soybeans. He's considering planting up to 50% of his corn acreage with rootworm-resistant hybrids next year, where necessary, to protect roots. The main reason: He likes the handling ease. “I can save about an hour a day not having to fill insecticide boxes.”

Pankonin will probably continue to use the Counter CR soil insecticide on the other half of his corn, which will include the 20% corn rootworm refuge areas. “I'll have more data next year to know if this is the right way to go,” he adds. “But so far, it looks pretty good.”

YieldGard Rootworm corn hybrids can be marketed as part of the Market Choices grain marketing program. This program identifies hybrids that are currently not approved for export to the European Union (EU). Farmers who are considering planting YieldGard Rootworm hybrids should check their grain marketing options before buying seed. For more information on this program, visit www.marketchoices.info.

For now, neither Terryberry nor Pankonin have concerns about marketing their corn. Both plan to either use it or sell it locally for cattle feed. Ruff and Davis say they've had no trouble finding local grain elevators that would buy it.

David Rhylander, director of trait marketing for Monsanto, says it's well worth the time to seek out elevators that will accept this new grain. “One hour on the phone discussing your grain marketing options could significantly increase your profitability — dollars that might otherwise be lost to rootworm feeding,” he says.

Two-Bug Control In One Seed?

Corn rootworm- and corn borer-resistant traits will be hitched together in 2004.

Corn Belt farmers planted about 400,000 acres of Monsanto's YieldGard rootworm-resistant corn after it gained EPA approval in late February 2003. In 2004, both the product's availability and planted acres should increase dramatically, according to industry officials.

One milestone that might pique farmer interest is EPA's recent approval of stacking Monsanto's YieldGard Rootworm and YieldGard Corn Borer resistant traits into one seed package. Monsanto will market this trait combination under the name YieldGard Plus.

“The goal is to get the necessary state-level regulatory approvals in the U.S. and import approvals in Japan for YieldGard Plus for the 2004 planting season,” says Todd DeGooyer, corn insect technology manager for Monsanto. “This approval will then pave the way for the industry's first triple-stack technology, YieldGard Plus with Roundup Ready corn, in later seasons.”

DeGooyer describes the possible 2004 state-by-state and Japanese approvals for YieldGard Plus as “highly likely,” with stacked traits being made available that fit the 90- to 110-day hybrid maturities. But even if approvals stall on stacked traits for next planting season, the corn rootworm resistance technology is performing well and gaining farmer appeal as a stand-alone product.

“In 2003, YieldGard Rootworm Bt (Bacillus thuringiensis) corn performance was excellent and provided superior protection compared to corn planted with insecticide and seed treatments,” DeGooyer says. “Especially from a consistency standpoint, this product is showing excellent performance. Unlike soil insecticides and seed treatments, there's almost no weather too dry or too wet to stop it from working.

“With 30 million acres infested with rootworms throughout the Corn Belt,” DeGooyer says, “it's exciting that this new technology is now available to farmers on a wide scale. We should have plenty of YieldGard Rootworm seed available for 2004, with more than 100 seed partners who will offer YieldGard Plus technology.”

Pioneer Hi-Bred International, Inc., will be one of several companies advancing multiple hybrids with the YieldGard Rootworm trait in 2004. However, according to Jerry Harrington, sales and marketing PR manager for Pioneer, his company's rootworm-resistant hybrids will be available in limited quantities only. He adds that Pioneer anticipates approval of its own rootworm-resistant trait, in cooperation with Dow AgroSciences, as early as 2005.

Mycogen Seeds expects “excellent interest, a good supply and good order activity where rootworm pressure is high,” according to Greg Cannon, communications manager. He adds that Mycogen will offer four different hybrids with the rootworm-resistant technology in 2004.

Dekalb and Asgrow, owned by Monsanto, should also have a good supply of YieldGard rootworm-resistant seed in 2004, says Kyle Maple, U.S. corn marketing manager. Maple notes that Dekalb and Asgrow brands combined will offer 12 YieldGard Rootworm hybrids, of which five will be stacked with Roundup Ready. Availability should especially be good for 110-day relative maturity hybrids.

To find out more about seed availability in a particular area, contact your local seed representative.

Rootworm-Resistant Hybrids: Pros And Cons

Potential advantages of rootworm-resistant hybrids:

  • Fewer handling, storage and calibration concerns.

  • Fewer health and human safety concerns.

  • Less need for insecticide and application equipment.

  • Less cost for insecticide and insecticide application.

  • Time savings during planting.

  • Fewer environmental concerns.

  • Fewer extreme weather concerns.

Potential disadvantages of rootworm-resistant hybrids:

  • Fewer marketing options (grain produced from a YieldGard Rootworm hybrid is not yet an accepted product in the EU).

  • Possible pollen drift concerns to neighboring fields planted to conventional corn.

  • Less planting flexibility (requires a 20% refuge area).

  • Insecticides are still needed on refuge areas.

  • Additional cost of new technology.