The emergence of weeds resistant to a popular herbicide is causing headaches for Midwestern farmers, forcing them to change how they manage weeds after years of spray-it-and-forget-it simplicity.
Weed experts say half the nation's farmland is dealing with the problem in some form or other. That includes farmers in Missouri and Illinois who have encountered half a dozen different species immune to glyphosate, the generic name for Monsanto's wildly popular herbicide Roundup.
Farmers are increasingly coming across aggressive varieties of superweeds that can't be killed by the herbicide that revolutionized modern farming.
The problem comes from using the same herbicide over and over on the same field with the same crop.