Balancing Act

July 27, 2012 07:57 AM
Balancing Act

Companies look to improve corn refuge compliance

Lance Panzier is convinced that the new refuge-in-a-bag style seed products are the best way to tackle insect resistance.
The new corn hybrids have been touted for their compliance factor because they automatically meet Environmental Protection Agency (EPA) regulations that require farmers to plant 5% to 20% of their corn using non-Bt seed. The goal is to forestall any insect resistance.
"EPA can’t police producers who say, ‘My neighbor is planting a refuge, so I can plant 100% Bt corn to get a better yield,’ " says Panzier, who farms 2,500 acres in Waltonville, Ill. "This levels the playing field and keeps everyone honest."
This year, Panzier planted half of his 1,000 corn acres with a refuge-in-a-bag product. On the remaining 500 acres, he used 20% non-Bt seed as a refuge and 80% Bt seed.
The beauty of the new-style seed, which is a combination of nontraited corn to serve as a refuge and Bt insect-protected corn premixed in one bag, is that the farmer can dump the seed into the planter and begin planting immediately without first having to change out the seed or calculate the necessary refuge acres.
This year marks the first season for the full commercialization of refuge-in-a-bag products that protect against rootworm, such as Dow AgroSciences’ Refuge Advanced powered by SmartStax, Monsanto’s Genuity SmartStax RIB Complete and the DuPont Pioneer Optimum AcreMax.

Help or harm?Insect refuges provide areas for insects to develop without being exposed to Bt toxins, a practice that is designed to slow resistance. Some entomologists, however, are concerned that, over time, these new products could hasten resistance in corn rootworm, the main pest targeted by the corn industry and by Bt insect-protected hybrids. Purdue University entomologist Christian Krupke says that the problem has to do with the premixing of refuge seed and Bt seed.

The conundrum. "On the compliance side, nothing else can beat refuge-in-a-bag. It guarantees there will be a refuge," Krupke says. "The issue is whether it’s better to have 100% compliance with the possibility of sublethal exposure and some damage to adjacent roots, or 60% to 70% compliance with a better refuge structure and no sublethal exposure. There is no perfect solution."
The problem is that refuge structure can be compromised because Bt corn plants are directly adjacent to non-Bt plants. "Rootworm larvae can feed on a refuge plant and eventually become large enough so that they then move to a Bt plant, feed on those roots and not die," Krupke says. "Conversely, larvae can feed initially on a Bt plant, not die, and then wander to a refuge plant. Both of these scenarios can and do occur underground."
On the positive side, interspersing Bt and refuge plants in a field brings the rootworm beetles closer together, which raises the odds that beetles that might be Bt-resistant will mate with those from the refuge that are susceptible, helping prevent resistance. Crossbreeding of these insects is why EPA developed the refuge requirements.
Corn rootworm resistance has been confirmed in Iowa and is suspected in other Midwestern corn fields containing the single Cry3Bb1 trait. Most of these fields have been planted to
hybrids with the same trait year after year, Krupke says.
This year, Panzier played it safe by planting only half of his corn acres using a refuge-in-a-bag seed product. "It’s brand new," he says. "I have my standby hybrids that I know work, but I now have one foot in each boat."

Crossbreeding of insects is precisely why EPA developed the refuge

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