Project Details:

Research to Integrate Best Management Practices for Glyphosate-Resistant Weeds in Soybean Production Systems (1920-172-0126-A)

Parent Project: Research to Integrate Best Management Practices for Glyphosate-Resistant Weeds in Soybean (1620-732-7235)
Checkoff Organization:United Soybean Board
Organization Project Code:1920-172-0126-A
Project Year:2019
Lead Principal Investigator:Bryan Young (Southern Illinois University)
Co-Principal Investigators:
Lauren Lazaro (Louisiana State University AgCenter)
Daniel B Reynolds (Mississippi State University)
Karla Gage (Southern Illinois University)
Aaron Hager (Southern Illinois University)
Mark Loux (The Ohio State University)
Jason Norsworthy (University of Arkansas Division of Agriculture)
Kevin Bradley (University of Missouri)
Reid Smeda (University of Missouri)
Greg Kruger (University of Nebraska)
Larry Steckel (University of Tennessee-Institute of Agriculture)
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Keywords: herbicide, resistance management, Weeds

Contributing Organizations

Funding Institutions

Information and Results

Comprehensive project details are posted online for three-years only, and final reports indefinitely. For more information on this project please contact this state soybean organization.

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Final Project Results

Updated April 1, 2020:
The progressive evolution and spread of herbicide-resistant weeds continues to challenge soybean production and grower profitability. The adoption of new technologies such as dicamba-resistant soybeans has ultimately improved weed control for some farmers, but has presented further challenges in terms of off-target movement of dicamba to sensitive plants and the potential for weed resistance to dicamba. The overall goal of this project continues to be the refinement of strategies that can be integrated into regional Best Management Practices (BMPs) for weeds to sustain soybean production and profitability. More specifically, practical field research will be conducted with a focus on soil residual herbicide interactions with cover crops, weed seed management, dicamba injury on sensitive soybean, monitoring weeds for resistance to dicamba and glufosinate (Liberty), and understanding the frequency of adverse weather patterns that prevent safe herbicide applications.

Our long-term goal is to develop management solutions for herbicide-resistant weed species to minimize their destructive impact on soybean production, as well apply the information from this research to improve management of other weeds in soybean that are evolving herbicide resistance or are generally considered problematic. The major research objectives addressed through this project are listed below. Specific objectives and field experiments are later discussed for each major objective.

Major Objectives:
1) Evaluate the biology of major herbicide-resistant weeds with respect to physiological and physical factors that contribute to their distribution, with emphasis on seed persistence and management in the soil seedbank.
2) Compare the implementation of various intensities of Best Management Practices for control of major herbicide-resistant weeds, or weed species that may shift to greater prevalence with current management systems.
3) Investigate challenges associated with successful implementation of tactics included in current Best Management Practices for control of herbicide-resistant weeds.
4) Coordinate outreach efforts among the principal investigators and the USB-funded outreach program on “Take Action”.

Research Findings and Deliverables:
The integration of non-chemical weed control methods to supplement herbicide use is necessary to provide greater sustainability of weed control technologies and reduce the risk of failed herbicide applications due to herbicide resistance. Research conducted in Arkansas, Missouri, and Illinois has demonstrated that use of combine chaff windrowing and subsequent burning can be an effective practice to reduce soil seedbank infestations of Palmer amaranth and waterhemp when used in combination with a diverse herbicide program and cereal rye as a cover crop. The second phase of this research involving mechanical mills attached to the back of combines to devitalize weed seeds in the chaff is still in progress. However, the relatively high plant moisture levels (crop and weed) at harvest has limited the effectiveness of this technology that has proven effective in more arid environments such as small grain production in Australia. Research will continue to make adjustments on this practice to determine the utility of this in U.S. soybean production.

Low doses of 2,4-D on Xtend soybean and low doses of dicamba on Enlist soybean have a similar impact on soybean growth and development as conventional or Roundup Ready soybean. In other words, Xtend soybeans are no less sensitive to 2,4-D than conventional soybean and Enlist soybeans are no less sensitive to dicamba than conventional soybean. Thus, the potential for off-target movement of these herbicides must be managed the same for any soybean genetics that don’t contain the appropriate herbicide resistance traits. Furthermore, repeated exposure of soybean sensitive to dicamba appears to be additive, or less than additive, excluding yield data to be collected in 2019. Commercial observations would have suggested that a second drift event of dicamba would have a synergistic effect on increasing soybean injury. However, our research would conclude that the greater levels of soybean injury may be due to the fact that the second dicamba exposure occurs later in the growth and development of soybean, which has a greater impact on soybean response than early-season applications. This information has already been presented to academic groups, state and federal regulatory agencies, and a journal article manuscript is being developed. Also, this information has been shared internationally with interested groups considering the use of Xtend crops. The data will continue to be used in presentations at various meetings and is planned for the development of a webinar with the Plant Management Network.

The farmer USB Directors were highly concerned with the potential for a shift in the sensitivity of major weed species to dicamba (Xtendimax) or glufosinate (Liberty) as a result of increased use of these herbicides for control of weeds with multiple herbicide resistance. Seed samples of Palmer amaranth, waterhemp, and horseweed (i.e. marestail) were collected in Fall 2018 over eight states and screened in the greenhouse to observe any variability in weed response to these herbicides. After the first year of research we have identified that some population differences exist for waterhemp response to glufosinate and horseweed response to dicamba. That information alone is highly valuable as we strive to prevent, or at least widely recognize, the potential for the progressive evolution of resistance to glufosinate and dicamba, as we failed to effectively manage this aspect with glyphosate resistance. This is not by any means confirming any weed resistance to these herbicides. However, these findings justify continuing the project and collecting weed seeds again in Fall 2019 to identify any negative trends in weed response to these herbicides.

Two webinars based on our research were recorded and posted with the Plant Management Network- Focus on Soybean.
1) Diagnosing Soybean Injury Caused by Dicamba - Bill Johnson, Purdue University, April 2019
2) Seed Burial and Persistence of Palmer amaranth and Waterhemp - Jason K. Norsworthy, University of Arkansas, May 2019.
In addition, the research findings from this project have been shared with media, extension educators, crop consultants, input suppliers, and soybean producers through integration in Take Action materials, website postings, newsletters, field days, and traditional grower meetings.

Project Years