ST. LOUIS, Oct. 10 (UPI) -- Weeds resistant to Monsanto's popular Roundup Ready weed-control system have been discovered in northwest Missouri.
On two separate soybean fields, scientists have found common waterhemp, also known as pigweed, that shows signs of resisting glyphosate herbicide.
Monsanto sells glyphosate as Roundup, a commonly used agricultural weed-killer that is the cornerstone of the company's Roundup Ready crop technology, the St. Louis Post-Dispatch reported.
The company has genetically modified soybeans, corn, cotton and
canola to withstand glyphosate so that growers can spray Roundup over the top of their fields to kill weeds without harming the crop.
But if the same crop and herbicide are used on a field, year after year, weeds with a natural genetic resistance to glyphosate will survive -- and thrive.
Eight species globally -- five in the United States -- have been classified glyphosate-resistant since 1996, according to a consortium of weed scientists.
Margaret Mellon, director of the food and environment program for the nonprofit Union of Concerned Scientists, said Monsanto should have contractually required farmers using its Roundup Ready crops to rotate them each year.