A quick check on your herbicide program: Are your modes of action actually working?

Eric Yu, UMN Extension Crops Educator, David Nicolai, UMN Extension Crops Educator, Debalin Sarangi, UMN Extension Weed Scientist

“Use multiple modes of action” has long been a cornerstone of herbicide resistance management. However, that recommendation only holds up if those modes of action are effective on the weeds present in your field. In many cases, herbicide programs that look strong on paper can fall short in practice. For descriptions of each herbicide mode of action, download the free Iowa State Herbicide Guide (see pages 21–24).

The new Check My Herbicide Plan tool was developed by GROW to help farmers and crop advisors take a closer look at their programs and determine how many active ingredients are truly effective against their target weeds.

There are several reasons why herbicide programs may not perform as expected. Herbicide-resistant weed populations, such as waterhemp in Minnesota, can significantly reduce the effectiveness of certain products. In other cases, premix herbicides may contain active ingredients at rates too low to adequately control specific weeds. To add to the complexity, different products may contain the same active ingredients under different brand names, making it difficult to recognize when modes of action are not as diverse as they appear. As a result, growers may unintentionally rely on fewer effective modes of action than intended.

The Check My Herbicide Plan tool helps address these challenges by guiding users through a simple process. After entering their location, crop, and target weeds, users can indicate any known or suspected herbicide resistance and input their herbicide program across application timings such as burndown, preemergence, and postemergence. The tool then generates a summary showing how many effective modes of action are being used in each pass. Results are displayed using a color-coded system, where green indicates effective active ingredients, orange suggests partial effectiveness, and red highlights those that are likely ineffective. Additional information is available to explain why certain products may not be performing as expected. This video provides a step-by-step overview of how to use the tool.

For Minnesota growers, this type of evaluation can be especially valuable when managing herbicide-resistant species like waterhemp. Identifying gaps in effectiveness ahead of the growing season can help reduce the risk of weed escapes and improve overall control.

It is important to view this tool as a starting point rather than a final recommendation. Herbicide selection should still be based on field history, scouting, and local expertise. In some cases, an herbicide that is not effective on one weed may still play an important role in controlling others. Working with Extension educators, crop consultants, or agronomists can help ensure that herbicide programs are both effective and well-rounded.

Overall, the Check My Herbicide Plan tool provides a practical way to evaluate herbicide programs with a focus on what matters most, using effective modes of action. By helping growers identify potential weaknesses before the season begins, it can support more consistent weed control and better long-term resistance management. For more details, see GROW’s article on this tool, and consider signing up on their website to receive updates on new tools and research related to integrated weed management.