Kansas farmers have requested information to help manage weeds in early planted soybeans. This is the second year of a two -year project to identify how soybean planting date influences the effectiveness of common residual herbicides used in both 15- and 30-inch row spacings.

1. Compare the duration of weed control by residual herbicides in soybeans planted in 15” and 30” rows prior to the crop insurance initial planting date (early) to soybeans planted shortly after the initial planting date (late).
2. Quantify the benefit of layered residual herbicides in terms of weed control and weed seed production when soybeans are planted early vs late in 15” and 30” rows.
3. Compare profitability among treatments evaluated.

This project will provide research-based information to farmer questions and will help understand how to manage herbicide-resistant Palmer amaranth in ways that slow the development of resistance to Group 15 herbicides. The budget and economic analyses will provide information on the profitability of the factors included in the study. This information will be shared with farmers through media outlets including newsletters, presentations, and field days.

Updated September 12, 2023:
Trials were established at Manhattan, Scandia, Ottawa, and Parsons. Weed control and photosynthetically active radiation data were collected during the summer. Weed biomass data are currently being collected in preparation for harvest. Data have been shared during field days at Parsons and Scandia. This research has been submitted for a student presentation at the North Central Weed Science Society annual meeting held in Minneapolis during December. Preliminary data analyses suggest there were no differences between Dimetric Charged and Authority MTZ for control of waterhemp , fall panicum, or yellow foxtail during 2023. Palmer amaranth control was greater with Authority MTZ at the early planting date, but greater with Dimetric charged at the later planting date.

Updated August 15, 2024:
All field research has been completed. Posters based on the second year of data were presented at the NCWSS (Dec 2023) and WSSA (Jan 2024) conferences (attached). The graduate student is working to collect survey data regarding farmer use of row spacing and residual herbicides. The graduate student is analyzing combined data (2022 and 2023) and writing thesis chapters.

View uploaded report

View uploaded report 2

Waterhemp control was greater that 90% regardless of treatments; however, Palmer amaranth control was 80% when sulfentrazone+metribuzin was applied late compared to over 95% control for all other treatments. The relationship between canopy coverage and weed control was examined and week associations were found. This corroborates research from the southeastern US that suggests herbicide program is more important than row spacing for weed control.

This project will provide research-based information to farmer questions and will help understand how to manage herbicide-resistant Palmer amaranth in ways that slow the development of resistance to Group 15 herbicides.