Our current trajectory for managing problematic weeds is not sustainable from a weed science or soybean production standpoint. Underutilized practices or tools that can improve and diversify our weed management practices must be adopted to at least slow the current rate of herbicide resistance evolution and spread in U.S. soybean production. Our field research across key US soybean production states investigated multiple cultural and chemical practices with the potential for integrating into modern soybean production. Project activity has been summarized by each Key Deliverable.
Key Deliverable #1 - Innovating and Integrating Non-Herbicidal Practices for Weed Management
Integrated weed management strategies that combine cover crops with residual herbicides have shown enhanced control of waterhemp and Palmer amaranth. Our research thus far indicates that a soil residual herbicide applied PRE on early-planted soybeans is still necessary to improve management of waterhemp and Palmer amaranth and cannot be replaced by using just a cereal rye cover crop in the early spring.
Deliverable #2 - Progressive Monitoring of Herbicide Resistance Evolution
Approximately 200 weed populations of waterhemp and Palmer amaranth were collected in Fall 2023 and screened in the greenhouse for sensitivity to 2,4-D, dicamba, and glufosinate herbicides, which represent the major herbicides used for postemergence control of these weeds in US soybean production. The frequency of waterhemp and Palmer amaranth survival to these herbicides in the greenhouse screen has gradually increased over time, which should sound the alarm that commercial resistance management tactics for these herbicides must be intensified before resistance proliferates to the extent observed with glyphosate on pigweed species.
Key Deliverable #3 - Improving Herbicide Recommendations on Pigweed with Multiple Herbicide Resistance
Field research data was generated on using the soil residual activity of metribuzin (e.g. Sencor, Tricor) with a greater focus on higher use rates and tank-mix partners to improve control of pigweed populations with multiple herbicide resistance. Thus far, our research indicates fairly robust soil residual control of waterhemp and Palmer amaranth can be achieved with higher application rates of metribuzin (>0.5 lb per acre active; >10 oz per acre of metribuzin 75%DF) combined with other herbicides such as Zidua, Authority, and Valor products.
The objective of a second field trial with metribuzin was to determine the crop safety and length of residual weed control from preemergence applications of metribuzin in early-planted soybeans. Another component tested was the difference in plant injury to soybean varieties described by the seed company as “above” and “below” average tolerance to metribuzin. The first year of trials were implemented in 2024 at 11 locations across the Midwest and data through the end of the field season is now being compiled to analyze and summarize the first-year results.
Key Deliverable #4 - Outreach
Our research findings have been disseminated in various formats to a wide audience, with a focus on soybean farmers as the primary target. Diverse mechanisms for outreach have been involved with delivering our key findings to clientele groups and include both grower and crop consultant meetings (virtual and in-person), field days, extension newsletter articles, webinars, and podcasts. Over the duration of this FY24 project, our team has delivered 305 unique presentations, publications, or other products, while reaching approximately 112,000 individuals with our message.