Twenty-seven states are now battling 13 confirmed glyphosate-resistant weeds, and chief among them are resistant marestail, ragweed, and waterhemp. Many growers across the U.S. are noticing that glyphosate or ALS-inhibitor herbicides alone do not effectively control weeds that can cause significant yield loss.
Purdue University weed scientist Bill Johnson says soybean fields must be managed proactively to ensure continued profitability.
“I think what tends to happen 99 percent of the time is management is not put in place until it is already present in the field. I think more time and effort needs to be spent in slowing the development of it by using more robust herbicide programs, more diversity on the modes of action on the front end, rather than having to manage a problem that’s developed from lack of management on the back end.”
Johnson recommends growers utilize a full-coverage, broad-spectrum weed management strategy for identifying and controlling resistant weeds.
“The first thing they have to do is recognize that they have it. They have to look for a patch of weeds that’s spreading. They have to look at their herbicide rates and do they feel like they have to consistently raise their herbicide rates or make multiple trips over the field to manage the weeds. And once they do that they need to go after that weed with at least two modes of action. So starting with a good clean field, a good stout, robust burndown program if they’re doing no-till utilizing residual herbicides to give early season suppression and then the ability to make timely post treatments and get a second active mode of action on that weed is very important.”
Growers who rely on glyphosate alone may find their herbicide programs falling short of expectations. The season-long approach to weed management combined with cultural practices, such as crop rotation and tillage, help growers reduce the weed seed bank and fight resistance.[audio:https://www.hoosieragtoday.com//wp-content/uploads//2012/05/Bill-Johnson-on-weed-resistance.mp3|titles=Bill Johnson on weed resistance]