Repeated use of herbicides with the same site of action can result in the development of herbicide-resistant weeds. This chart, developed by Michigan State University weed specialist Christy Sprague, groups herbicides by their mode of action and site of action to help you diversify product use and delay the development of resistance.
Pay close attention to the site of action group numbers. Many chemical manufacturers now include these numbers on the label, in a box marked "Group/Herbicide."
Bob Hartzler, Iowa State University Extension weed management specialist, advises that designing an integrated weed control program involves more than randomly adding different herbicide classes. "The product must have good activity on the important weeds in the field to successfully reduce selection pressure," he says.
For example, a Group 2 herbicide would provide little benefit against waterhemp since many biotypes are resistant to these herbicides.
Download the Corn and Soybean Herbicide Chart.