Reducing pesticide risk in soybean production

By Melanie Leclerc

With the concerns of pollution and the negative impact of agriculture on the environment always increasing, there is pressure on producers to reduce the risks associated with the use of pesticides on their farm. The development of weed resistance to herbicides has also led producers to reassess their approach to pest management . In field crop production, farmers are hesitant to move to organic agriculture or other reduced pesticide practices because of the challenges in weed management. This is particularly true with soybean crops because weed pressure often increases in years 2 and 3 of the transition phase from conventional to organic production.

It has become evident that there is a need to develop weed management strategies to help soybean producers reduce their pesticides use and eventually move to organic production.

In 2006 and 2007, on-farms trials were conducted in Southern Ontario by researcher Dr. Darren Robinson of the University of Guelph’s Ridgetown campus in collaboration with OACC. Dr. Robinson evaluated the efficacy of three weed management strategies for soybean: the first treatment was Conventional zero-till which is 2 applications of glyphosate made to soybeans at the 1st and 4th trifoliate leaf stage; the second treatment was Integrated Weed Management (IWM) which is an in-row banded application of the growers’ traditional herbicide program (made at the 1st trifoliate) plus interrow cultivation at the 4-5th trifoliate stage of the soybeans; and finally, the third treatment, using an organic method, which consisted of an interrow cultivation and hand-weeding at the 1st and 3rd trifoliate leaf stages.

A cost benefit analysis and a measure of risk reduction (Environmental Impact Quotient or EIQ) were performed for each of these practices. The factors considered in the cost of weed control were the herbicide, fuel and hand-weeding costs. The EIQ is a measure of potential risk of pesticides to farm workers, consumers and the environment. Finally, field days were held to demonstrate the trials and to survey the likelihood of growers to adopt practices to reduce pesticide risks.

The trials were performed in fields with different degrees of weed infestation: low, moderate and high. Yields were variable throughout the different fields but generally higher in the conventional treatment. The results showed that, with the exception of fields with low weed infestation, soybean grown during will likely require very high input costs. In fact, for fields with moderate weed infestation, the cost of weed management was generally 50-100% higher in the IWM and organic treatments than in the conventional treatment. If a price premium can be guaranteed for ‘transitionally-grown’ soybean, the additional cost of organic transition might be justified. As expected, the impact on the environment (EIQ) was zero with the application of the organic treatment. In conditions of heavy weed infestation, Integrated Weed Management does not necessarily translate to lower EIQ when compared to the conventional treatment. In this study, a second herbicide application was made in the IWM treatment in the fields with high weed infestation, resulting in a higher EIQ. Field days offered good opportunities for growers to observe differences between low, moderate and high weed infestations, and the likely outcome of growing soybean during the transition phase of organic certification.

The survey revealed that a majority of producers are interested in adopting techniques to reduce risk related to the application of pesticides on their farm. Some producers expressed that they were using or may use reduced rates or fewer herbicide applications. A majority of farmers also use or have used practices such as increased seeding rate, pre-plant tillage, direct or zero-till planting and plough-down crops.

The problem of weed control, yield reduction and need for equipment have been identified as constraints in the adoption of reduced pesticide risk practices; better crop prices were seen as the biggest incentive. Workshops and field demonstrations are good ways to educate producers about reduced risk practices. Respondents also indicated that cost benefit analysis, more time to research, subsidy programs and different equipment would help them reduce pesticide use. Two growers who participated in the trial have expressed interest in transitioning a portion of their farm into organic production.

There are good resources available to help producers who are interested in organic production. These include: production handbooks, workshops, internet courses, technical bulletins, extension specialists, and successful farmers willing to share experiences.


This research was funded by Agriculture and Agri-Food Canada’s Pesticide Risk Reduction Program. Views expressed in this article are not necessarily those of AAFC.


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Posted April 2008