Weed Control for More Sustainable Soybean Production

Project Overview

LNC95-090
Project Type: Research and Education
Funds awarded in 1995: $80,000.00
Projected End Date: 12/31/1998
Matching Non-Federal Funds: $41,820.00
Region: North Central
State: Minnesota
Project Coordinator:
Nicholas Jordan
Dept of Agronomy and Plant Genetics, University of Minnesota

Annual Reports

Commodities

  • Agronomic: soybeans

Practices

  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, farmer to farmer, focus group, on-farm/ranch research, participatory research
  • Pest Management: biological control, chemical control, competition, eradication, integrated pest management, physical control, weed ecology
  • Production Systems: agroecosystems
  • Sustainable Communities: partnerships, public participation

    Abstract:

    [Please note: the Final Report for this project also covers the SARE Project ANC95-026, which has the same title.]

    The overall objectives of our work were to: (1) determine the effectiveness of the bacterial biocontrol, Pseudomonas syringae pv. tagetis (PST) and competitive soybean varieties for control of Canada thistle in organic and no-till soybean production systems, and (2) to support development of new sustainable farming systems for the north-central region by initiating a broad-based cooperative research approach to develop integrated cultural and biological weed management.

    Field studies were conducted in 1996 and 1997 to determine the effectiveness of the bacterial biocontrol, Pseudomonas syringae pv. tagetis (PST) and competitive soybean varieties for control of Canada thistle in both organic and no-till production systems. The competitive soybean variety “Kato” improved the efficacy of two cultivations for the control of Canada thistle and had numerically lower values with respect to height and seed production for Canada thistle when compared to the non-competitive variety “Evans” in organic soybean production. Kato reduced the total weed density and total weed dry shoot weight when compared to Evans in no-till soybean production but did not affect marked Canada thistles in no-till production. Soybean yield was independent of soybean variety.

    PST reduced Canada thistle survival by 33%, 69%, 91%, and 93% in 1996 and by 11%, 32%, 68% and 70% in 1997 at 35, 51, 73 and 107 DAP respectively in organic soybean production. In no-till soybean production, PST reduced Canada thistle survival by 5% and 50% at 48 and 105 DAP in 1996 and by 16%, 28% and 60% at 48, 69 and 105 DAP in 1997 respectively. Canada thistle plants that survived treatment with PST were shorter and less likely to produce seed than untreated controls in both organic and no-till soybean production.

    Differences in the efficacy of PST for control of Canada thistle in organic and no-till production could not be explained. PST had no impact on soybean yield. Two cultivations in organic soybean production did not improve soybean yield or weed control except in Kato where extra cultivation reduced both Canada thistle height and the average number of seed heads produced per plant.

    The combination of Kato plus PST plus two cultivations always resulted in the lowest values for Canada thistle seed production and generally the greatest reductions in Canada thistle height suggesting that cumulative effects of multiple weed control measures in an integrated weed management program may successfully control this weed.

    In no-till soybean production, the herbicide bentazon was more effective at reducing Canada thistle survival, height and seed production than PST but did not improve soybean yield suggesting that weed control measures in addition to post-emergent applications of imazethapyr and sethoxydim were not necessary to maintain soybean yield in this study.

    Lack of yield differences between weed control treatments could not be explained. A Minnesota-based biocontrol company is cooperating with the University of Minnesota to develop the PST bacterium as a commercial weed control product.

    In 1996-97 we worked to initiate a broad-based cooperative research approach to develop integrated cultural and biological weed management. An important outcome of our many discussions between farmers, researchers and extensionists is that we shifted the emphasis of our work from research to farmer learning.

    We are currently establishing “learning communities” (LCs) composed of farmers, local extension educators, and research and extension weed scientists that will develop integrated cultural and biological weed management methods for soybean production. Each LC will work together to examine and adapt systems thinking tools, such as agroecosystem analysis, to devise an integrated weed management method. Each group will use the integrated weed management method experimentally, assess its practical value, help develop practical and convenient means for using the approach, and help refine it. A network of LCs could accelerate farmer learning about local challenges that arise in farming systems at farm, watershed and larger scales. Ultimately, LCs could have a significant and lasting impact on the way universities conduct agricultural research.

    Introduction:

    Weed management has focused on tillage and selective herbicides to reduce the impact of weeds on crop yields. While effective, chemical and mechanical control has led to excessive soil erosion, herbicide resistant weeds, and contamination of surface and groundwater. Integrated weed control methods including weed competitive crops and biological controls are now being investigated.

    Field studies were conducted in 1996 and 1997 to determine the effectiveness of the bacterial biocontrol, Pseudomonas syringae pv. tagetis (PST) and competitive soybean cultivars, for control of Canada thistle. These experiments were conducted in organic and no-till production systems.

    The competitive soybean variety “Kato” improved the efficacy of two cultivations for the control of Canada thistle and had numerically lower values with respect to height and seed production for Canada thistle when compared to the non-competitive variety “Evans” in organic soybean production. Kato reduced the total weed density and total weed dry shoot weight at 105 days after planting (DAP) by 43% and 55% respectively when compared to Evans in no-till soybean production but did not affect marked Canada thistles in no-till production. Soybean yield was independent of soybean variety.

    PST reduced Canada thistle survival by 33%, 69%, 91%, and 93% in 1996 and by 11%, 32%, 68% and 70% in 1997 at 35, 51, 73 and 107 DAP respectively in organic soybean production. In no-till soybean production, PST reduced Canada thistle survival by 5% and 50% at 48 and 105 DAP in 1996 and by 16%, 28% and 60% at 48, 69 and 105 DAP in 1997 respectively. Canada thistle plants that survived treatment with PST were shorter and less likely to produce seed than untreated controls in both organic and no-till soybean production.

    Differences in the efficacy of PST for the control of Canada thistle in organic and no-till production could not be explained. PST had no impact on soybean yield. Two cultivations in organic soybean production did not improve soybean yield or weed control except in Kato where extra cultivation reduced both Canada thistle height and the average number of seed heads produced per plant.

    The combination of Kato plus PST plus two cultivations always resulted in the lowest values for Canada thistle seed production and generally the greatest reductions in Canada thistle height suggesting that cumulative effects of multiple weed control measures in an integrated weed management program may successfully control this weed.

    In no-till soybean production, the herbicide bentazon was more effective at reducing Canada thistle survival, height and seed production than PST but did not improve soybean yield suggesting that weed control measures in addition to post-emergent applications of imazethapyr and sethoxydim were not necessary to maintain soybean yield in this study.

    Lack of yield differences between weed control treatments could not be explained. The herbicide bentazon reduced total weed density and weed dry shoot weight by 68% and 84% respectively and Canada thistle survival was reduced 30%, 34%, 96% and 97% in 1996 and 24%, 52%, 88% and 95% in 1997 at 34, 48, 69, and 105 DAP respectively. These findings suggest that competitive soybean varieties and biological weed control are valuable components of an integrated weed management system.

    We are establishing “learning communities” (LCs) composed of farmers, local extension educators, and research and extension weed scientists that will develop integrated cultural and biological weed management methods for soybean production. Each LC will work together to examine and adapt systems thinking tools, such as agroecosystem analysis, to devise an integrated weed management method.

    Each group will use the integrated weed management method experimentally, assess its practical value, help develop practical and convenient means for using the approach, and help refine it. A network of LCs could accelerate farmer learning about local challenges that arise in farming systems at farm, watershed and larger scales. Ultimately, LCs could have a significant and lasting impact on the way universities conduct agricultural research.

    Project objectives:

    1. Compare weed control of Canada thistle in an organic production system using competitive soybean varieties and bacterial biocontrol to current cultivation- and labor-intensive methods.

    2. Compare weed control of Canada thistle in a no-till production system using competitive varieties, bacterial biocontrol, and reduced herbicide rates to current herbicide-intensive methods.

    3. Collaborate with member organizations of the Sustainers’ Coalition of the Minnesota Institute for Sustainable Agriculture in presentations, discussions and evaluations of research findings at summer field days and winter workshops.

    4. Initiate a broad-based cooperative research approach to develop integrated cultural and biological weed management, in order to reduce sediment and herbicide pollution associated with weed control, and support development of new sustainable farming systems for the north-central region.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.