Pesticide risk reduction in soybeans by comparing conventional, organic and integrated weed management systems and soybean cultivar traits

Project Code PRR06-490

Project Lead

Andrew Hammermeister - Organic Agriculture Centre of Canada

Objective

To compare the efficacy of conventional, integrated, and organic weed management strategies in soybean through on-farm demonstration trials

Summary of Results

Farmers hesitate to transition towards adopting practices involving reduced use of pesticides, including organic production, due to challenges in weed management. With the continuous rise in adoption of reduced till practices, key weed management challenges for soybean farmers are the development of weed resistance to herbicides in zero-till systems and the lack of sustainable, integrated systems approaches to weed control that do not rely solely on herbicide use.

To address these issues, researchers from the University of Guelph and the Organic Agriculture Centre of Canada, in collaboration with the soybean industry in Ontario compared three weed management strategies in soybean production: i) conventional zero-till with standard herbicide use; ii) integrated weed management (IWM) with band-spraying herbicides in crop row and mechanical control between rows), and iii) organic transition with mechanical and manual weed control.

The research was conducted on conventional crops in commercial farms in Ridgetown area of Ontario. Except for eliminating the use of herbicides, in the organic transition plots did not incorporate any other crop management strategies typically used in organic production.

The project aimed to demonstrate to growers the economic and environmental costs along with benefits and risks associated with these strategies and assist them in making informed weed management choices. In this 2-year study, the strategies were compared for effectiveness in reducing weed density and biomass, economics (cost-benefit), measure of herbicide risk reduction potential and yield in soybean fields with different degrees of weed infestation (low, moderate and high).

Overall, the results varied depending on the levels of weed infestation, composition of weed populations (weed types) present in the field and the dynamic of weed development during the growing season. Here is a synopsis of the findings:

Weed control was generally higher in the conventional plots than the IWM and organic plots in the fields with low weed infestation. The trend was not as clear, but weed control under IWM was superior to the conventional system in some fields with moderate and high weed infestation.

Soybean yields were generally highest in the conventional system followed by the IWM and organic systems in the fields with moderate and high weed infestations and comparable between conventional and IWM systems in fields with low weed infestation.

The cost of weed management was generally 50-100% higher in the IWM and organic systems compared to the conventional system in fields with moderate weed infestation. Differences were not as apparent in the other fields, but cost was generally higher in the organic plots due to the labor cost for hand-weeding where this practice was used to remove weeds within the row.

The herbicide risk, measured as the Environmental Impact Quotient (EIQ) was always lowest (zero) in the organic system and varied between the other two systems. The EIQ was higher in the conventional system than in IWM system in fields with low weed infestation and the opposite in fields with moderate and high weed infestation. Additional herbicide applications were needed to suppress higher weed levels in these fields under IWM, resulting in higher EIQ.

Summer field tours were held in the trial sites to demonstrate findings from this study emphasizing the likely outcomes of growing soybean during the gradual process of transitioning away from herbicide use. The tours attracted a large number of local soybean growers, industry representatives, researchers, and government specialists. Growers were surveyed about the likelihood of shifting away from the chemical-based conventional approaches to adopting alternative weed management practices as part of their crop production system. The majority of respondents indicated interest in alternative approaches and many had already adopted practices such as increased seeding rate, pre-plant tillage, direct or zero-till planting and plough-down crops to minimize herbicide use. However, challenges with obtaining acceptable levels of weed control, potential of yield loss and the costs involved, especially for special equipment required to accomplish an operation were identified as key constraints preventing growers from adopting more advanced, lower pesticide risk weed management practices.

The study concludes that soybean is an economically challenging crop to grow during the phase of transitioning from conventional to moderate pesticide use (e.g. through integrated pest management) or to organic systems. With the exception of fields with low weed infestation, soybean production during the transition phase will likely require very high input costs due to weed control requirements which is mainly due to higher cost of hand and mechanical weed control. Hand weeding is typically used only on smaller acreages, or for spot removal of particularly problematic weeds.

Soybean is not typically grown as an early transitional crop going into organic production due to its poor competitiveness with weeds. During transition, farmers will instead use more competitive crops, adjust tillage systems and adopt cultural control methods (e.g. increase seeding rate, seedbed preparation, cultivar selection, planting date) to improve weed management. Soybean is often the first crop following transition, to take advantage of its high value, as opposed to growing it as a transitional crop where no premium is available.

The study recommends financial incentives, subsidy programs and availability of more adaptable mechanical weeding equipment to assist growers overcome the economic challenges of transitionally-grown soybean. This assistance, coupled with education and demonstration of validated technologies will help growers offset additional transition costs and promote adoption of alternative weed management practices.

For more information about this project, please contact Dr. Andrew Hammermeister at ahammermeister@nsac.ca or visit the Organic Agriculture Centre of Canada website to view the following articles:

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