This project was funded by the Minnesota Soybean Research and Promotion Council in FY23. One graduate student (Ph.D.) was recruited, and two staff members (Researcher 3 from Sarangi Lab and Researcher 6 from Lorenz Lab) are working part-time on this project. Field research trials were conducted in 2023 at UMN’s Rosemount Research and Outreach Center near Rosemount, MN, and we are requesting funding in FY24 to repeat the field trials and take some additional parameter measurements from this research. At least two years of field trial data are required to validate the results and publish peer-reviewed journal articles. Some results from the 2023 trials are included in the methodology section. This research was demonstrated at the 2023 Corn and Soybean Weed Management Field Day, which was attended by 47 attendees including farmers, agronomists, industry representatives, and UMN Extension Educators. The results will also be presented at the North Central Weed Science Society meeting in Minneapolis in December 2023 and the UMN Extension’s Research Update meetings and MN Ag Expo in January 2024.
Herbicide-resistant weeds are reducing the yield and quality of soybean grown in Minnesota; therefore, an integrated weed management approach is required to manage this problem. Early canopy closing by soybean plants can inhibit late-season weed emergence and suppress the germinated weed seedlings. Thus, fewer weed seeds will be added to the seedbank and mixed with soybean grain as foreign materials. The selection of early canopy-forming soybean varieties can help in achieving this goal. On the other hand, factors such as soybean planting date and herbicide application can delay canopy formation. Tank-mixing soil residual herbicides (herbicide site of action Group 15; e.g., Dual II Magnum, Zidua, and Warrant) with foliar-active postemergence treatments (such as Roundup or Liberty) are now frequently recommended for late-season weed control, especially for the control of waterhemp and other pigweed (Amaranthus) species. These soil residual herbicides are known to cause soybean injury when applied postemergence; however, limited data is available to assess the canopy closure delay in soybean due to these herbicide applications. Moreover, evaluating the importance of variety selection, row spacing, and planting date on soybean canopy closure and late-season weed control is also important. The objectives of this research are to evaluate: 1) the impact of foliar-active postemergence herbicides applied with or without soil-residual herbicides on soybean injury, canopy closure, and yield, 2) the effect of soybean variety and planting date on late-season weed control and canopy formation, and 3) the relative time required for canopy closure by the commercially available soybean varieties in statewide variety trial. The field experiments will be conducted in Rosemount, MN in 2024.

1. Evaluate the impact of foliar-active postemergence herbicides applied with or without soil-residual herbicides on soybean injury, canopy closure, and yield
2. Assess the effect of soybean variety selection and planting date on canopy formation and late-season weed control
3. Assess canopy closure for the statewide variety trials to measure differences in time to close the canopy

This team comprises two faculty (Sarangi, and Lorenz) who are heavily involved in soybean variety development, production, breeding, and weed management works in Minnesota. Sarangi is the state Extension Specialist who reaches out to growers, crop advisors, and other stakeholders frequently and advises them on weed management in soybean. The results of this research will be demonstrated in summer Field Days in Rosemount, MN in 2024. The information obtained from this research will also be disseminated using online platforms, including but not limited to, the MN Crop News (over 1,600 subscribers), regional Extension Crop newsletters, radio spots, Strategic Farming talk series, and Minne-Line articles. Social media platforms such as Twitter, and YouTube will be used to share research updates and short videos. The results will be presented at the Extension events such as Crop Pest Management (CPM) Short Course, Research Update for Ag Professionals, Prairie Grain Research Update, Best of the Best Crop Management, and MN Ag-Expo. 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.

The proposed research will evaluate the factors that impact soybean canopy closure. Early canopy closure can provide better weed suppression and be used as an integrated management tactic for herbicide resistance management. The weeds that germinate later in the season not only compete with soybean and reduce yield but also can increase foreign materials in soybean and reduce product quality. Therefore, the factors that promote accelerated canopy closure in soybean will inhibit weed seed germination in the late season and can suppress the germinated weed seedlings. The goals outlined in this research are timely. The results of this research will improve soybean yield, quality, and profitability. Postemergence residual herbicides that cause the least soybean injury without any delay in canopy closure can be used in the future for waterhemp control. Soybean varieties that close the canopy earlier can be used in the future for the management of herbicide-resistant weeds. Depending on the results of this research, seeds of known UMN breeding lines with fast canopy closure will be increased and used in future experiments. Finally, information on genetic variation for canopy closure and its effect on weed control will inform soybean breeders on the usefulness of breeding for this trait, ultimately leading to more varieties available with fast canopy closing properties.