Resistance to multiple herbicides a growing challenge

Published on: 17:30PM Sep 22, 2009
Chuck Foresman

Remember when weed control required a cocktail of chemistries? Remember when new products instantly solved tough problems? Remember when those new products stopped working? 
Weeds do. 
Within a weed population, a few plants naturally have resistance to any herbicide. However, as a herbicide is used over and over, growers select for weeds that carry that resistance gene. And once a large portion of a population carries that gene, it is passed down through generations, allowing weeds to “remember” that they are resistant to certain chemistries.
If resistance to a single mode of action can make weed management programs a challenge, resistance to multiple modes of action can make weed management nearly impossible. But multiple resistance is a reality. In southern Illinois, 23 counties have waterhemp resistant to one or more of these four modes of action: ALS-inhibitors, glyphosate, PPO-inhibitors and triazines. Missouri has tri-resistant weeds (glyphosate, PPO-inhibitors and ALS-inhibitors). In Indiana, no-till soybean growers are facing horseweed (marestail) populations resistant to both glyphosate and ALS-inhibitors.
To manage this challenge, weed scientists recommend using multiple herbicide modes of action to avoid selecting for resistance to one commonly-used product. That’s also why rotating herbicide modes of action is key for resistance management. 
Do you have weeds resistant to more than one herbicide? How do you manage them? Check out for some ideas.