Herbicide-resistant weeds are reducing the yield and quality of soybean grown in Minnesota; therefore, an integrated weed management approach is needed to manage this problem. Early canopy closing by soybean plants can inhibit late-season weed emergence and suppress the germinated weed seedlings. Thus, a smaller number of weed seeds will add to the weed seedbank and enter the soybean seeds 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 the canopy closure. Tank-mixing soil residual herbicides (herbicide site of action Group 15; e.g., Outlook, Dual II Magnum, Zidua, and Warrant) with postemergence treatments are now frequently recommended for late-season weed control, especially for the control of waterhemp and other 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 by soybean due to these herbicide applications. Moreover, evaluating the importance of variety selection 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 residual postemergence herbicides and Liberty herbicide application 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 for canopy closure by the commercially available soybean varieties in statewide variety trial. The field experiments will be conducted in Rosemount, MN in 2023. A graduate student will be mentored as a part of this research, and Extension articles and peer-reviewed journal articles will be published. The results of this research will be demonstrated in Extension and outreach events.

1. Evaluate the impact of residual postemergence herbicides and Liberty application on soybean injury, canopy formation, and yield

2. Assess the impact of variety selection and planting date on canopy formation and late-season weed control

3. Canopy closure assessment 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 2023. 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, Facebook, 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 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.

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Updated April 19, 2024:

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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 late-season weed 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.