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Study: Adopting new Bt corn is age-old decision for farmers

You can't teach old farmers new tricks for controlling corn rootworms.

A Purdue University study found that as farmers approach late middle age, they are less likely to plant corn that produces Bacillus thuringiensis (Bt), a protein that kills corn rootworms and European corn borer insects that feed on plant tissues.

The 2004 study was based on surveys and discussions with about 1,000 Indiana farmers who grew at least 200 acres of corn. Researchers also found that farmers experienced in biotech crops are more likely to plant Bt corn hybrids, while some growers are less inclined to use Bt varieties because they find planting parts of their fields in non-Bt "refuge" corn a hassle.

As young farmers become more comfortable with biotechnology, their adoption of genetically modified corn seed increases, said Corinne Alexander, a Purdue agricultural economist and the study's lead researcher. Older farmers who've never planted Bt hybrids aren't likely to start, however.

"What we found was that age was a significant predictor in Bt corn adoption," Alexander said. "We found as producers get older and gain experience they are more likely to adopt Bt corn rootworm, but once they reach about age 48 they become less likely to adopt the technology."

The reasons, Alexander said, include time and profit potential.

"For those farmers who are much closer to retirement, they receive a much smaller benefit from trying something new because they are only going to be farming for, say, another five or 10 years," she said.

Indiana is an interesting case study for genetically modified corn adoption because the state has areas with severe, moderate and low corn rootworm problems, Alexander said.

"How a farmer controls corn rootworm in Indiana really depends on what sort of pest pressure they face," Alexander said. "In southern Indiana, most farmers wouldn't treat for it at all because there are very few corn rootworm larvae in that part of the state. In the moderate region in northeast and central Indiana, farmers may use soil insecticides or seed treatments for control. In the high pressure northwest corner of Indiana, most farmers use soil insecticides and some use seed treatments."

The control dynamic changed in 2003 when Monsanto Corp. introduced a genetically modified corn resistant to corn rootworm. Seed with the corn rootworm Bt protein became widely available for growers in 2004. Despite the new insect resistance traits, only 21 percent of Indiana's corn was planted in biotech varieties in 2004, compared to 47 percent nationally, according to the U.S. Department of Agriculture.

Producers now have four options in the corn rootworm fight, Alexander said. "They've got the no treat option. They've got the seed treatment option. They've got the soil insecticide option. And, now, they have the Bt corn rootworm option."

The Purdue study also found that preventing non-Bt corn from being pollinated by nearby Bt corn crops is a factor in producer adoption of the biotech seed. In addition, some farmers indicated that the extra effort in planting non-Bt refuges in or near their Bt corn crops discourages them from planting the corn rootworm-resistant seed.

"Farmers who are very concerned about pollen drift contaminating adjacent fields were significantly less likely to adopt Bt corn," Alexander said. "We also did a series of focus groups with producers. We asked them to agree or disagree with the statement, 'I will not plant a corn rootworm resistant variety because of the refuge requirement.' What was surprising was farmers who strongly agreed with the statement were also significantly less likely to adopt corn rootworm corn.

"What this indicates is that there's a small group that dislikes the refuge requirement and, because of that, they are not planting Bt crops. But by and large, producers said refuges were not that big a deal -- just follow the rules, plant them and it doesn't take much extra time."

Farmers who plant Bt corn are required by the U.S. Environmental Protection Agency to plant 20 percent of their acreage within, around or adjacent to those biotech crops in non-Bt corn hybrids.

Among other findings in the Purdue study:

Growers who have planted genetically modified corn to control other corn pests would plant corn rootworm Bt hybrids, if given the opportunity. "We found that producers who had planted Bt corn that controls European corn borer in 2003 were significantly more likely to plant corn rootworm corn," Alexander said.

Europe's refusal to purchase many biotech grains -- and the influence that decision has had on corn buyers within the United States -- leaves some Indiana corn growers hesitant to plant corn rootworm-resistant hybrids.

"If producers are thinking about planting corn rootworm-resistant corn, they will first want to make sure their buyer is willing to buy that corn," Alexander said. "You wouldn't want to plant corn rootworm corn without checking with them because it doesn't so much matter what the European Union wants, what really matters is what your buyer wants."

Thuy Van Mellor, a research associate, assisted Alexander in the Purdue study. The study, titled "Determinants of Corn Rootworm Resistant Corn Adoption in Indiana," appeared in a recent edition of AgBioForum and can be read online at

You can't teach old farmers new tricks for controlling corn rootworms.

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