Giant ragweed soon could cast a giant shadow on the world's most popular herbicide. Researchers at Ohio State and Purdue universities have confirmed glyphosate-resistant giant ragweed populations in Indiana and Ohio. Glyphosate is the active ingredient in herbicides such as Roundup and Touchdown, which are used for burndown weed control in no-till cropping systems and postemergence in Roundup Ready soybeans and corn. The weed species is the seventh in the United States to show resistance to glyphosate.