Waterhemp (Amaranthus tuberculatus) is the most troublesome weed species in soybean fields in Minnesota. Waterhemp populations resistant to different herbicides have been identified in the state. A recent study funded by the Minnesota Soybean Research and Promotion Council confirmed that 86% waterhemp populations surveyed in Minnesota were resistant to glyphosate. The same study also confirmed the presence of waterhemp resistant to six herbicide sites of action including auxin mimics (2,4-D and dicamba). Recently, a farmer from Dodge County, MN, contacted Sarangi Lab to report a failure in waterhemp control in his field following multiple Liberty (glufosinate) applications. We conducted a field bioassay in 2023 and the experiment confirmed the reduced sensitivity of this population to glufosinate. Numerous recently approved soybean traits (Enlist E3, XtendFlex, LLGT27, and Liberty Link) are engineered for glufosinate resistance along with other herbicides. The widespread distribution of glyphosate-resistant waterhemp in the United States forced the farmers to use glufosinate for waterhemp control. Therefore, the spread of this putative glufosinate-resistant waterhemp could be detrimental for the soybean growers in Minnesota and other midwestern states. Moreover, glufosinate-resistant Palmer amaranth (Amaranthus palmeri), a closely related species to waterhemp, has been reported in Arkansas and North Carolina. Knowledge about the degree and mechanism of glufosinate resistance in this waterhemp population from Minnesota is critical. Such information would help to identify the causes of evolution and mechanisms for the spread of glufosinate-resistant waterhemp. Specific objectives of this research are to: 1) confirm the presence of glufosinate-resistant waterhemp in Minnesota; 2) elucidate the genetic and physiological mechanisms of the glufosinate resistance in waterhemp. A graduate student will be mentored, and peer-reviewed and Extension articles will be published. Research results will also be demonstrated in Extension and outreach meetings in 2024 and 2025.

1) To confirm glufosinate resistance in a waterhemp population in Minnesota.
2) To elucidate the genetic and physiological mechanisms of glufosinate resistance in waterhemp.

Upon confirmation, the DOD will be the first reported waterhemp population in the world to become resistant to glufosinate. Sarangi will collaborate with Dayan at Colorado State University to accomplish the experiment goals. Sarangi is an Extension Weed Scientist with experience in working with herbicide-resistant waterhemp for many years, and Dayan is well-known for his work on molecular Weed Science and glufosinate resistance. The information obtained from this research will be disseminated using web-based platforms, including but not limited to, the MN Crop News (over 1,600 subscribers), regional Extension Crop newsletters, radio spots, the Strategic Farming webinar series, and Minne-Line articles. Social media platforms such as Twitter and YouTube will also be used to share research updates. The results will be presented at Extension events such as the Crop Pest Management (CPM) Short Course, Research Update for Ag Professionals, the Prairie Grains Conference, the Best of the Best in Wheat & Soybean Research Conference, and the Minnesota Ag-Expo in 2024 and 2025. Most of the audiences at these events are agronomists, farmers, fertilizer/plant protection dealers, and independent crop consultants. One graduate student will be mentored as a part of this project and this research will be part of their thesis work. Peer-reviewed journal articles will be published from this research.

Updated September 2, 2024:
The seeds of putative Liberty-resistant waterhemp were collected from a farmer's field in Minnesota, and greenhouse screening for the resistance is ongoing (objective 1). Objective 2 will be performed at Colorado State University in the spring semester of 2025. A graduate student (Ph.D.) is recruited to conduct this research. Any definitive results will be available in the summer of 2025.

Liberty (glufosinate) is used very frequently in soybean in Minnesota and other states. The Enlist E3, XtendFlex, LLGT27, and Liberty Link soybeans are resistant to Liberty, and the discovery and spread of Liberty-resistant waterhemp would be detrimental for the soybean growers in the United States. The goals outlined in this research are timely and need immediate attention. Liberty-resistant Palmer amaranth is already reported in Arkansas and North Carolina, however, to our knowledge, there is no report of Liberty-resistant waterhemp yet. Therefore, to stop the spread of this Liberty resistance in waterhemp, we must understand their mechanism of resistance. For example, if the resistance is due to reduced absorption, one could overcome this problem using appropriate adjuvants. This research will improve the yield and quality of Minnesota grown soybean in the short- and long-term.