2023 Wisconsin Waterhemp Herbicide Resistance Screening Project


Rodrigo Werle


September 30, 2023

Send in Waterhemp Seeds for Free Herbicide Resistance Screening!

According to our stakeholders, waterhemp (Amaranthus tuberculatus) continues to be the most difficult-to-control and concerning weed species in Wisconsin corn-soybean production systems. This summer we received several calls regarding lack of complete post-emergence waterhemp control with Callisto and/or dicamba in corn and with Enlist One in soybean. As harvest approaches, we are being asked by our clientele if our program would test such concerning waterhemp populations for resistance to Callisto, dicamba, and/or Enlist One. When our clientele needs assistance, our response is always YES!   

Thus, we would invite Wisconsin farmers, agronomists, and industry representatives to collect waterhemp seeds this fall from Wisconsin corn and soybean production fields where Callisto, dicamba, and/or Enlist One didn’t provide satisfactory post-emergence waterhemp control and submit them to the UW-Madison’s Wisconsin Cropping Systems Weed Science lab for herbicide resistance screenings.

We intend to screen the waterhemp samples in the greenhouse for resistance to Callisto (mesotrione; Group 27), Enlist One (2,4-D; Group 4), dicamba (Group 4), and glufosinate (Liberty; Group 10). Results will be made available to those who submit the samples after the greenhouse screenings are completed.

There is no cost associated with the herbicide resistance screenings. The only cost will be your time to collect the seed samples and mail them to:

Please download and print the SEED COLLECTION FORM (PDF file) for information on how to collect the waterhemp seeds and fill out the information necessary for the project for each field. Please submit the form with the seed sample. Samples will only be included in the herbicide resistance screening if the information requested in the SEED COLLECTION FORM is provided.

Figure 1. Waterhemp seedlings growing in the UW-Madison Walnut Street greenhouse for a comprehensive, Wisconsin state-wide assessment of waterhemp response to a diverse group of POST herbicide sites of action. Picture by UW-Madison Weed Science Graduate Research Assistant and WiscWeeds Herbicide Resistance Screening Coordinator Felipe Faleco.

We anticipate the preliminary herbicide resistance screening results will be available in the fall of 2024 (it takes ~6 months to screen samples for herbicide resistance in the greenhouse and we typically start our screenings after March when environmental conditions in our greenhouses are appropriate for waterhemp growth).

For questions, please contact Dr. Rodrigo Werle via e-mail: rwerle@wisc.edu.

We thank those submitting waterhemp seed samples and the Wisconsin Soybean Marketing Board, the Wisconsin Corn Growers Association, and the Crop Protection Industry for supporting this effort.