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Kai Ryssdal: Turning a profit while you till your field is what farmers try to do. One of the big variables about that is deciding which seeds to plant. For the past 15 years or so, more farmers have been choosing genetically-modified seeds for crops bred with specific traits, like resistance to insects or to drought.
Today the National Research Council released a report evaluating the profitability of those genetically-modified crops. From the Marketplace Sustainability Desk, Caitlan Carroll reports.
CAITLAN CARROLL: This report says farmers spend less on pesticides and get bigger crops from genetically-modified seeds.
Peter Raven heads the Botanical Garden in St. Louis and contributed to the report. He says the sturdier the crops, the less time farmers have to spend weeding and watering.
PETER RAVEN: The main benefit from growing GM crops for farmers is that they get about 30 percent of their time back.
KEITH RYAN: Yeah, I don't know if I would necessarily agree with 30 percent less time. It certainly is a lot more efficient.
That's Keith Ryan. I caught up with him as he was planting corn on his farm in Taylorville, Ill.
Ryan says when you have built-in traits, like insect resistance, you don't have to drench the crops with insecticide.
RYAN: You don't have to mess with getting all the insecticide on you personally and deal with the ramifications that come with that down the road.
But the report says a number of weeds are developing resistance to Round-Up, a popular weed killer that doesn't damage genetically-engineered crops.
Analyst Bill Freese at the Center for Food Safety says the South is seeing some of the worst effects of this new resistance.
BILL FREESE: There are weeds down there that farmers are using seven or eight different chemicals and still can't kill. So now they're going back to hand weeding, which hasn't been seen for decades.
Authors of the report say farmers' heavy dependence on Round-Up contributed to this situation. Farmer Keith Ryan says as other herbicides have come down in price, farmers have been using them in tandem with Round-Up. But weed resistance is inevitable.
I'm Caitlan Carroll for Marketplace.