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, based on surveys and discussions with about 1,000 Indiana farmers who grew at least 200 acres of corn, also revealed 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, says 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 age was a significant predictor in Bt corn adoption," Alexander says. "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 says, 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."

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 says.

"How a farmer controls corn rootworm in Indiana really depends on what sort of pest pressure they face," she says. "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 USDA.

"Producers now have four options" in the corn rootworm fight, Alexander says. "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 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 says.

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

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 www.agbioforum.org/v8n4/v8n4a01-alexander.htm.