Source: University of Wisconsin College of Agricultural and Life Sciences



The best way to win a battle is to not fight the battle in the first place. This is certainly the case with herbicide resistant weeds. If weeds don't become resistant, growers can keep using existing herbicides to control them. Most recently, glyphosate-resistant weeds have been at the top of the list of concerns. Roundup Ready crops were launched in 1996 and the first report of a glyphosate-resistant weed in the U.S. was horseweed (or marestail) in the year 2000.



"Across the Midwest, we saw the potential of resistance if growers were only going to use glyphosate in corn and soybeans without using other herbicides or practices to break up the cycle," says Chris Boerboom, UW-Extension weed scientist.



Because of this risk, UW-Extension hosted a Glyphosate Resistance Roundtable in 2003 for Wisconsin's agricultural groups to discuss the risk of glyphosate resistance and comment if continued education was needed. With this meeting, Wisconsin's major commodity, consulting, and retail associations became national leaders and endorsed a Glyphosate Stewardship White Paper, which supported practices to avoid developing resistance.



During the past five years, no cases of glyphosate-resistant weeds have been documented in Wisconsin while most other Midwest states have reported one or more glyphosate-resistant weeds such as giant ragweed, common ragweed, waterhemp or horseweed.



"We"ve spent a lot of time with Wisconsin corn and soybean growers discussing resistance and practices to reduce the risk of glyphosate-resistant weeds," Boerboom said. "I think most of our growers and their advisers are doing a relatively good job using diverse weed management programs."



What might set Wisconsin apart? An important practice to slow or avoid the development of resistance is to reduce the number of times glyphosate is used, which can be done by rotating herbicide modes of action. It could be using conventional herbicides in corn and then using glyphosate in soybeans or it could be using a preemergence herbicide followed by glyphosate in the same season.



As it turns out, Wisconsin corn and soybean growers may be national leaders in the practice of using multiple herbicides or rotating herbicides. Paul Mitchell, UW-Extension agricultural economist, notes, "We just completed a national survey of corn, soybean, and cotton growers on their weed management practices and found Wisconsin growers were unique. Growers in Wisconsin were more likely to rotate herbicides than corn and soybean growers in any other state, which is likely a major reason we have not had glyphosate-resistant weeds in Wisconsin yet."



Mitchell and Boerboom hope that growers and the agriculture industry in Wisconsin remain leaders in glyphosate stewardship and leave the glyphosate-resistant weed battles to other states. However, they both agree that glyphosate-resistant weeds will eventually show up in Wisconsin and growers will have to spend more to control them. Mitchell and Boerboom hope to delay that day as long as possible.