Brazil’s southernmost state yesterday launched a big publicity push to keep farmers from illegally planting genetically modified soybean seeds smuggled in from neighboring Argentina. A black market is growing for the seeds, which save farmers money on herbicides and pesticides. Industry sources estimate that nearly 10 percent of Brazil’s soybean harvest could be genetically modified, despite a national ban against GM crops. Brazil is the world’s second largest soybean producer after the U.S. Ads will run encouraging law-abiding farmers to tattle on ones planting GM seeds, and ads will also warn that police will set illegal crops on fire. Monsanto is fighting in the Brazilian courts to be able to sell its GM soybeans legally, but last month Greenpeace won a court ruling forcing the company to conduct a one-year environmental impact analysis before it can sell the seeds.