Production Blog

Negotiate the Bt Maze

Pam Smith
By  Pam Smith , Crops Technology Editor
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Managing western corn rootworm requires a system approach to management which includes digging and looking at roots and managing traits. (DTN photo by Pamela Smith)

I end up with a sloppy mess of alphabet soup each time I write about insect traits. More than one copy editor has cried about the necessity to list the Cry3Bb1, Cry1F, Cry1A.105, Cry2Ab, Cry34/35Ab1 components of SmartStax, for example.

Do corn growers really care that DuPont Pioneer's new Optimum Leptra combines Optimum Intrasect which is the Herculex I (Cry1F) with YieldGard Corn Borer (Cry1Ab) with Agrisure Viptera (Vip3A)? Is it necessary to know that Syngenta's new Agrisure Duracade 5122 E-Z Refuge trait stack (Cry1Ab, Cry1F, mCry3A, eCy3.1Ab) differs from Agrisure Duracade 5222 E-Z Refuge because the latter contains Viptera (Vip3A) for additional above-ground protection. Is it important that the new Powercore hybrids pending from Dow AgroSciences don't contain the Cry3Bb1 protein, which make them SmartStax without corn rootworm traits?

This week I attended the University of Illinois AgMasters meeting and listened to University of Minnesota entomologist Ken Ostlie detail the challenges western and northern corn rootworms are presenting to Bt trait technologies. It's been 10 years since Bt traits for corn insect protection were introduced, and those farming in corn rootworm regions know the insects are challenging the rootworm proteins. So far, above-ground traits appear to be hanging tough, but they are higher-dose proteins than rootworm traits.

"A lot of growers in Minnesota thought transgenic corn would put corn rootworm out of business," said Ostlie. By 2011, he said, growers in his state were combining many tactics and investing significant amounts of money in corn rootworm management. "All of this on top of traits that should be working," Ostlie said. "We even started seeing some evidence of cross resistance -- which means a grower switches to one trait that isn't working and the other trait still doesn't work as well.

"All of a sudden, things weren't so simple anymore," Ostlie said.

It's human nature to embrace a technology that works. It's easy to say we wish we'd been more proactive and safeguarded the technology. It's hard to go back once something is simple. Traits are like automatic transmissions and cruise control. It takes more thought and effort to drive them manually.

That's exactly why you need to know and manage that alphabet soup of proteins within these hybrids. I've had more than one grower tell me the maze of insect traits combined with differing refuge requirements are too complicated to negotiate.

Tough. Rootworms don't move much. So unlike glyphosate-resistant weeds that can sometimes be established through pollen transfer or physical movement of seed, insect trait performance in your fields is most likely going to be a direct reflection of your management practices. Use a trait over and over and the rootworm will win. Managing those traits is one way to make sure traits continue to be viable in the future.

Fortunately, the entomologists Chris DiFonzo of Michigan State University and Eileen Cullen of the University of Wisconsin keep updating a Bt trait table that is the equivalent of a road map for this maze. You can find it here:…. Southern growers will need to adjust refuge requirements.

You don't have to keep the alphabet soup in your head. You just need to use it.

Pamela Smith can be reached at


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12/9/2013 | 9:44 AM CST
The elephant in the room would be root causation for resistance. What is the point at which the advantage of genetically modified plants are outweighed by the inevitability of their failure? I'm confounded at the continued push towards the use Bt traits in seeds. Producers are usually very forward thinking, and as the issue of resistance continues to mount, where is the tipping point? We are seeing similar results to the rampant use of antibiotics on antibiotic resistant bacteria. Compared to antibiotic use, introduction Bt traits are in a relatively infant stage. Perhaps there is still time to mitigate what appears to be inevitable.