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Corn after corn changes rootworm game

The outbreak of failures to control rootworm in fields planted to corn that get its genetic tolerance from a certain trait, the Cry3Bb1 event, has farmers everywhere asking questions. Farmers who grow corn after corn are especially concerned.

Reports from Western states, where rootworm feeding on the supposedly genetically protected corn is most prevalent, say it’s most common to find the problem in fields that have been in corn for a long time.

Here’s a farmer’s question, answered by agronomists who are Certified Crop Advisers: I have one farm where I have grown corn after corn for five years and will be growing corn there this year. Should I do anything different this year because of the unfolding rootworm control issue?

Key Points

Rotate rootworm traits in continuous corn situations.

Soil insecticides may provide a second mode of action in some cases.

Reconsider plans and rotate out of corn, if possible.


“Selection pressure is greater in corn-after-corn acres, so your concern is warranted,” says Andy Like, agronomist with Daylight Farm Service, Daylight. “If you have not been rotating rootworm traits, that would be my first suggestion to avoid a potential resistance problem.

“Monitor the performance of your rootworm-traited corn going forward. If a resistance problem shows up on your farm, it will likely be on continuous corn acres.”

Scout closely

Dan Ritter, Extension ag educator in Newton County, believes scouting is key. “This is a farm I would scout closely, as a corn-on-corn situation can encourage larger populations of corn rootworms, especially after corn five years in a row,” Ritter says. “It would be great if you could rotate to soybeans. If you’re committed to corn in this field, evaluate using a different technology or perhaps using a granular insecticide.

“Long-term continuous corn using the same Bt [event] is how some of the problems you’ve heard of got started,” he adds.

To Traci Bultemeier, it’s all about refuge. “Refuge, refuge, refuge — that’s the key,” she says. Bultemeier is an account manager for Pioneer Hi-Bred International Inc., based in Fort Wayne.

“Genetic control of corn rootworm will likely provide the best response in the event that you have a rootworm infestation,” she says.

Switch traits

Like Ritter, Bultemeier believes the smart money for this field may be on switching traits, especially if the farmer has been using the same one for five years. Some believe a second mode of action can help provide better control. This second mode of action can be provided by additional genetic traits, higher rates of seed treatment (insecticide) or soil-applied insecticide.

“In those areas that experience heavy corn rootworm feeding each year, a soil-applied insecticide may have merit, especially when it comes to control of secondary pests,” Bultemeier says.

“Regardless of your decision on corn rootworm trait package or soil insecticide additions, refuge requirements still need to be followed properly on traited acres. Doing so will assist you in being able to continue using traits effectively.”

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Scout, rotate, refuge: This trio of recommendations from agronomists applies if you’ve already grown corn in a field for several years, even if you would rather plant corn there again.

This article published in the March, 2012 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.