Reduced-Risk Strategy for Integrated Weed Management in Field Vegetables

For inquiries regarding this strategy, please contact:
Pesticide Risk Reduction, Pest Management Centre, Agriculture and Agri-Food Canada

August 2016


Pesticide Risk Reduction (PRR) of Agriculture and Agri-Food Canada's (AAFC) Pest Management Centre. To reduce undesirable impact of the use of pesticides in agriculture, PRR works with grower groups, industry, provinces, researchers and regulators to identify gaps in pest management and opportunities to develop and implement strategies to address these.

A pesticide risk reduction strategy is a detailed plan that aims to address grower needs for reduced-risk management tools and practices for specific pest issues. The strategies are developed through extensive consultation with stakeholders. The strategy document presented here summarizes the framework and activities supported by PRR. It is intended to provide an update on the progress in developing and implementing the strategy and new tools and practices made available through this process.

For more information, please visit the Pest Management Centre.


PRR acknowledges the contribution of participating organizations and stakeholders, including current and former members of the Integrated Weed Management Working Group:

  • Kristen Obeid and Anne Verhallen of Ontario Ministry of Agriculture and Rural Affairs;
  • Clarence Swanton, Robert Grohs, Darren Robinson, Laura Van Eerd and Rene Van Acker of University of Guelph, Ontario (ON);
  • Danielle Bernier and Mario Leblanc of Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Quebec. Quebec (QC);
  • Viliam Zvalo and Rosalie Madden of Perennia, Nova Scotia (NS);
  • Shauna Mellish and Stephanie Compton of Prince Edward Island Department of Agriculture, Prince Edward Island (PE);
  • Gavin Graham and Claude Bertheleme of New Brunswick Department of Agriculture, Aquaculture and Fisheries, New Brunswick (NB);
  • Luc Brodeur, formerly of Phytodata (QC), Stephanie Sanchez and Karine Verstricht of Prisme (QC), Connie Achtymichuk of Saskatchewan Ministry of Agriculture, Saskatchewan (SK);
  • Susan Smith and David Ralph of British Columbia Ministry of Agriculture and Land, British Columbia (BC);
  • Chris Neeser of Alberta Agriculture and Forestry, Alberta (AB), and Rob Nurse, Diane-Lyse Benoit, Bonnie Ball Coelho, Aaron Mills, Marie-José Simard and Kevin Sanderson of Agriculture and Agri-Food Canada.

Executive summary

The need for alternative weed management tools and practices for field vegetable crops was identified as a high priority issue through stakeholder consultation. Field vegetables are of great economic significance in Canada and adequate weed management is essential for viable vegetable production. Traditionally in these crops weeds are managed primarily through repetitive use of the few herbicides available. However, some of these herbicides are facing resistance issues and some are undergoing regulatory re-evaluation and certain uses may be lost as a result. The issue was thus deemed to offer good potential both for risk reduction and to benefit the sector through the development and implementation of a reduced risk management strategy.

This report summarizes the collaborative efforts, activities and progress of the Pesticide Risk Reduction's work since 2003 in support of developing and implementing a reduced-risk weed management strategy for field vegetables in Canada. The objective was to address grower needs for lower risk herbicides and non-chemical approaches suitable for inclusion in integrated weed management (IWM) systems. The goal is to reduce risks to humans and to the environment from herbicide use in vegetable crops and help growers achieve viable weed management while mitigating the risk of resistance development to herbicides.

This strategy was developed through consultations and collaborations with key stakeholders and weed management experts including provincial specialists, university and government scientists and vegetable industry representatives across main vegetable growing provinces. Many of these stakeholders have been actively involved in an expert working group tasked to develop the IWM strategy. As part of the strategy, key pest management gaps were identified, reduced-risk solutions to address these gaps were prioritized, and an action plan to develop and implement these solutions was put in place.

Over the past 13 years, the PRR has funded 15 projects aimed at developing reduced risk weed management solutions, including 4 screening trials to identify alternative weed control products. As of 2016, key outputs for growers include:

  • recommendations for integrated weed management approaches combining a variety of tools and practices such as banded herbicide sprays and use of cover crops;
  • a decision support tool for the selection of suitable cover crops for use on farms;
  • a critical weed-free period determined for carrot crops for the proper timing of weed control measures;
  • regulatory packages leading to the registration of at least 22 new herbicide uses, representing at least 5 new modes of action in various vegetable crops.

More details about the outputs of this strategy are provided in Table 1. These results have been regularly communicated to growers to promote their uptake and proper use. It is anticipated that adoption of the new tools and practices will enable a move away from full reliance on herbicides by growers, thereby minimizing risks of resistance development in weeds and reducing pesticide loads in the environment.

Pest management and pesticide risk reduction issues

Field vegetables are important crops grown annually on about 100,000 hectares across all provinces and contributing a farm gate value of $950 million (2014). Ontario and Quebec have the largest vegetable acreages (90% of national acreage combined) and provide about 83% of Canadian production volume. Vegetables are among the most intensive cropping systems, with high input and maintenance operations to ensure maximum yields and quality to meet increasing demand for fresh and processing markets.

Weeds are a major limiting factor in vegetable production and herbicide use has been the main approach to achieve acceptable weed management in the past. However, the development of resistance within weed populations has become an issue in recent years due to the repetitive use of the few available chemicals. For instance, resistance to linuron, one of most heavily used herbicides and one of the few weed control options in organic (muck) soils, has been reported in ragweed and pigweed. Moreover, linuron is currently under Health Canada's regulatory review for continued registration. The final decision is pending, but the review may result in the phase-out of some uses of linuron, potentially leaving growers with fewer control options. Finally, improper identification of weed species and lack of awareness of alternative control options may lead to unnecessary use of herbicides and loss of their efficacy due to resistance.

The overarching issue identified through this strategy was the lack of a variety of control options in the tool-box to enable sustainable weed management in multiple field vegetables crops.

This strategy was thus centered on developing new knowledge and making available lower risk weed management tools and practices to assist growers in the transition to implementing integrated weed management.

Strategy development

Stakeholder consultations from as far back as the establishment of the Pest Management Centre in 2003 identified high priority weed management gaps for vegetable crops. This led to several projects supported by the Program between 2003 and 2008 to evaluate herbicides and other control methods. Product screening and evaluation trials generated efficacy and crop tolerance data required to support regulatory submissions to Health Canada's PMRA for registration of new herbicide uses. This aimed to make new herbicides available to replace the older ones, and to increase the number of active ingredients available in the tool box to mitigate resistance development. These trials and submissions were in addition to herbicide priorities addressed annually through the Minor Use Pesticides processes since 2003 (not shown here).

In the late 2000s, it became apparent that a concerted effort was needed to allow for broader stakeholder consultations engaging expertise from various regions and specialties, and to focus more on alternatives to chemical controls and integrated weed management approaches.

Working group consultations

A working group was established in summer 2009 to provide expert advice to PRR in developing a strategic direction to achieve sustainable weed management in vegetable production. This group consists of provincial vegetable and weed specialists, researchers, and extension experts serving the vegetable industry. Since its inception, the working group has been involved in a number of consultations and regular exchanges of information and ideas mainly through teleconferences and email updates. In November 2009, several members met in person at the Canadian Weed Science Society (CWSS) annual meeting in Charlottetown, Prince Edward Island. In fall 2011, a subset of the working group engaged in a series of consultations devoted to increased adoption of cover crops for the purpose of weed management in vegetables.

Priority issues and gaps

Discussions within the working group over the years led to identification of these key weed management issues and gaps:

  • Need for lower risk products and new modes of actions to replace uses lost to resistance or re-evaluation and to enable rotation among various chemical families;
  • Lack of a variety of effective tools and practices allowing the adoption of integrated weed management strategies and a reduction in the exclusive reliance on a few herbicides, and which would support the organic vegetable sector;
  • Lack of effective programs for herbicide resistance management, for example, to address redroot pigweed and ragweed resistance to linuron (used extensively in carrots);
  • Lack of adequate replacement products for atrazine; loss of atrazine in BC has led growers to rely on Basagran (bentazon) only for weed control in sweet corn;
  • Lack of grower awareness on available cultural weed control methods, proper weed identification and appropriate selection of herbicides and other control measures;
  • Lack of knowledge on the effects of various rotation systems (for example, tomato following sweet corn) and control practices on herbicide residue and weed seedbank dynamics;
  • Cover crops were shown to be a useful weed management practice, but information to support selection of plant species suitable for Canadian vegetable growing regions needed to be made readily available to growers;
  • Lack of knowledge on the ecology and seed bank dynamics of key herbicide resistant weed species and lack of rapid resistance testing technique for early detection of resistant weeds.

Action plan

Three key goals were identified to address the above priority issues and gaps:

  1. Establish knowledge base to support informed management decisions
  2. Develop new reduced-risk weed control solutions
  3. Communicate and promote adoption of reduced risk solutions resulting from the strategy.

Based on these issues and identified goals, an action plan focussed on solutions recommended by the working group was developed to implement a reduced risk IWM strategy. Summarized in Table 1, this action plan includes the goals, milestones (specific solutions proposed by the working group) as well as progress on the PRR's work to address these solutions and advance the strategy implementation.

Table 1 – Action plan to implement a reduced-risk strategy for weed management in vegetable production in Canada (August 2016)

Goal 1. Establish knowledge base to support informed management decisions
Milestones Status Implementation Activities Completion period
Greater understanding of ecology and seed bank dynamics of herbicide resistant weed species found in vegetable crops In-progress AAFC project PRR16-010 - Early detection, monitoring and management of herbicide resistant weeds in field vegetables. The project aims to conduct field surveys and screening for resistant weeds across Ontario and Quebec, and develop molecular tool for rapid detection of resistant weed species. The goal is to help growers make informed in-season weed management decisions by avoiding use of herbicides which will not be effective against their weed populations. This approach is expected to address the limitations of the classical resistance testing method which requires several months to produce results, thus being only useful for the following growing season. 2016-2019
Assess the effect of critical weed free periods, crop density, crop spacing, fertility program, and cultural practices on weed/crop competition Completed

Partially addressed by AAFC project PRR07-260 – Determination of the critical weed-free period in carrots grown on muck and mineral soils. Maximum duration that carrot crops must be free of weeds, without compromising yield, is until the 12 leaf stage of crop growth. Based on this finding, carrot growers are recommended to scout fields for weeds until carrots are at the 12 leaf stage. This critical weed-free window may occur over a shorter duration when carrots are seeded later in the season and weed infestation is moderate to low.

Assess the effect of critical weed free periods, crop density, crop spacing, fertility program, and cultural practices on weed/crop competition In-progress Critical weed-free periods to be determined for other vegetable crops grown in muck and mineral soils and share existing information about previously published critical weed-free periods. Note: A list of Critical Weed-Free Periods is already available for many crops, including vegetables on Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) web page. Not applicable
Develop interactive weed identification and herbicide selection tools Future A need was put forward to develop a web-based interactive tool (searchable database) for vegetable crops to help growers and extension service personnel to identify weeds and make informed decisions about herbicide choices. A tool similar to ( was suggested, previously developed for corn and soybean. The province of Quebec has also made available a tool called Sage Pesticides (in French only) ( to help growers with recommendations on pesticide choices for crops (including relative human and environment toxicity values) and enable the judicious use of pesticides. Not applicable
Investigate the potential of using cover crops as part of integrated weed management Completed

AAFC project PRR10-010 – Literature review on applications of cover crops as part of integrated weed management systems in vegetable production in Canada. The review identified 4 approaches suitable for weed management that can be recommended for adoption to Canadian vegetable growers. Some of these recommendations were the subject of further research work under this strategy aiming to validate the approach under Canadian growing conditions.

Develop a cover crops selection tool Completed

AAFC project PRR12-020 – Development of a cover crop selection decision-making tool for vegetable production in Eastern Canada. A new, bilingual interactive Cover Crops Selecting Tool was launched in 2014. Grower's in Canada's eastern provinces (Ontario, Quebec, Prince Edward Island, New Brunswick, and Nova Scotia) can use the tool to identify the cover crop best suited to meet their needs depending on specifics of their farm and the desired beneficial attributes.

Status legend:
  • Activity addressing a milestone or part thereof is underway (In-progress)
  • Activity is complete (Completed)
  • Areas recommended for further work or promotion (Future)
Goal 2. Develop new reduced-risk weed control solutions
Milestones Status Implementation Activities Completion period
Develop integrated strategies to reduce herbicide use through targeted herbicide applications' Completed AAFC project PRR06-700 - Reduced risk weed control strategies in carrot production in organic & mineral soils. Integrated approaches identified for broadleaf weed control were banded application of herbicide combined with mechanical cultivation (for example, using side knives between the beds) which reduced herbicide use by 66%; and combination of broadcast herbicide application prior to carrot emergence, followed by a single cutting at 3 leaves stage of carrots, thus reducing herbicide use by 50% for carrot production on mineral and organic soils, respectively. 2006-2009
Evaluate efficacy of reduced risk herbicides Completed AAFC project MU03-WEED1 - Evaluation of low risk weed management options in sweet corn, tomatoes, sugar beets, peppers, cole crops and vine crops. Efficacy and crop tolerance data were generated to support 7 registrations of 5 products and 4 User Requested Minor Use Label Expansions (URMULE) submissions. 2003-2007
Completed AAFC project MUR06-030 - Evaluation of low risk weed management options in snap beans, lima beans, carrots, red beets, pea, and dry bean. Efficacy and crop tolerance data were generated to support six new herbicide uses, including 1 new registration and 5 URMULE submissions. 2006-2008
Completed AAFC project MUR06-100 - Reduced risk herbicides for horticultural crops in organic soils: supplemental registration data and herbicide screening. Work undertaken in Ontario and Quebec on onions, lettuce, Chinese cabbage and celery. Results were inconclusive for Chinese cabbage and celery. Efficacy and crop tolerance data was generated to support submission of pendimethalin for use in lettuce and label expansion for flumioxazin and also recommendations on using flumioxazin for post-emergence broad leaf control in onion grown in muck soils. Pendimethalin (onion) and flumioxazin (onion and celery) uses have been then registered. 2006-2008
Completed AAFC project SCR07-002 - Processing peas herbicide screening trial. Efficacy and crop tolerance assessments confirmed that four of the herbicides evaluated in this study: imazamox+imazethapyr (Odyssey), flumioxazine (Château), dimethenamid-P (Outlook) and halosulfuron-methyl (Sandea) were considered effective and safe to be pursued for registration for broadleaf weed management in processing peas. Imazamox+imazethapyr and flumioxazin have been subsequently registered. 2007
Future Identify potential bioherbicides suitable for use in both organic and conventional vegetable production in Canada. Not applicable
Investigate the use of cover crops in combination with other cultural techniques Completed AAFC project PRR07-040 - Evaluation of reduced-risk weed management approaches for annual grass control in sweet corn. The efficacy and benefits of using various cover crops as living-mulches were assessed. Although weed control achieved with living mulches alone was lower, yields did not differ from the industry standard, indicating that using living mulches may be a viable pesticide-free weed management option in sweet corn. Combined with herbicides, living mulches provided an added benefit of improved season-long weed control. 2007-2010
Completed AAFC project PRR11-030 - Cover crops and zone tillage for reduced risk weed management in field vegetables in eastern Canada. A key conclusion is that use of cover crops in spaghetti squash can be a good supplemental weed control that reduces the need for chemical control and the overall weeding costs, while increasing marketable yield, and providing good disease and erosion control. 2011-2014
Future Examine alternative techniques such as using cover crops in rotation or in between the crop rows, tillage, banding applications of bioherbicides for weed management in organic production. Not applicable
Future Examine alternative weed control approaches (for example, combining herbicides with cover crops) in vegetables under plastic and in field and processing tomato. Not applicable
Future Evaluate equipment available for the destruction of cover crops (efficacy, cover crop re-growth, speed of destruction, cost of equipment, cost of operation, facility of use and adjustments). Not applicable
Investigate mechanical weeding Future Evaluate crop tolerance and weeding efficacy of different mechanical weeders used in vegetable crops. Not applicable
Status legend:
  • Activity is complete (Completed)
  • Areas recommended for further work or promotion (Future)
Goal 3. Promote adoption of reduced risk solutions resulting from the strategy
Milestones Status Implementation Activities Completion period
Technology transfer: Demonstrate to growers the use and benefits of new tools and practices Completed AAFC Project PRR10-080 - Demonstration of reduced use of herbicides in carrot crops through chemical banding and mechanical cultivation in Prince Edward Island. Banded herbicide sprays combined with cultivation between the rows using S-tines and side-knives reduced herbicide use by 66% with no negative impact on yield when compared with industry standard. Cost benefit analysis showed herbicide banding to be economically feasible. 2010-2012
Completed AAFC Project PRR10-090 - Demonstration of reduced use of broadleaf herbicides in carrot crops through chemical banding and mechanical cultivation in Nova Scotia. Banded treatments reduced herbicide use by approximately 50%, with no significant differences in weed control and yield when compared with broadcast application. A cost benefit analysis showed that the banded treatment was more expensive than the broadcast method. 2010-2012
Completed AAFC Project PRR10-120 - Demonstration of reduced use of broadleaf herbicides in potato crops through chemical banding and mechanical cultivation in Quebec, Prince Edward Island, and New Brunswick. Banded herbicide sprays in potato crops reduced the amount of herbicide use by 50%, while providing efficacy and yield comparable to broadcast. About 25 potato growers and stakeholders were directly involved in the on-farm demonstrations. 2010-2012
In-progress AAFC project PRR16-030 - Integrated weed management: on-farm demonstration of recommended cover-cropping techniques for weed management in cucurbit (squash) production. The project aims to demonstrate to growers how to adopt and incorporate into commercial squash production systems alternative weed management techniques developed through the previous project PRR11-030. 2016-2018
Share information and develop effective communication materials to facilitate transfer of knowledge Completed Critical window of weed-free period established for carrots - PRR07-260 - and relevant recommendations were incorporated into Ontario's Vegetable Crop Production Guide. A bilingual factsheet titled Weed Management in Carrots was also published on OMAFRA website. 2009

Two factsheets were developed and published on AAFC website regarding herbicide banding technology in carrot crops - PRR06-700 and PRR10-080:

Two Ministère de l'Agriculture, des Pêcheries et de l'Alimentation (MAPAQ) factsheets on banded herbicide technology were translated from French to English and published online:

Completed A factsheet Field Vegetable Production: Using Cover Crops for Weed Management featuring recommendations resulting from the literature review (PRR10-010) was published on AAFC website. A poster titled 'Using cover crops as an integrated weed management tool in field vegetable production' also highlighting these findings was presented at the Ontario Fruit and Vegetable convention in winter 2011. 2010-2011
Completed A factsheet A web-based cover crop decision tool for growers in Eastern Canada describing what the tool is about and how it can be used for successful adoption of cover crops is published on AAFC website. A poster titled "On-line Cover Crop Match-Making Service: Find the right cover crop for you!" was presented at the Ontario Fruit and Vegetable convention in winter 2015. 2014-2015
Status legend:
  • Activity addressing a milestone or part thereof is underway (In-progress)
  • Activity is complete (Completed)

Outcomes from the strategy

The major outcomes anticipated from the implementation of the tools and practices resulting from the reduced-risk weed management strategy in field vegetables include:

  • Better rotation and resistance management opportunities offered through the addition of several lower risk herbicide uses, with new modes of action, to the weed control tool-box;
  • Recognized herbicide application techniques, such as banded sprays providing beneficial integrated approaches to growers for reducing herbicide use up to 66% without compromising yield and also reducing the risk for herbicide resistance development;
  • Adoption of cover crops made possible by generating basic knowledge on cover crop species and their benefits, and making available a cover crop decision support tool for use by growers, thereby lowering the need for synthetic inputs;
  • Carrot growers are able to accurately identify the weed-free window when weed management measures are warranted to maintain yields, thereby avoiding unnecessary sprays and reducing management costs;
  • Growers are more aware of and more likely to adopt new technologies made available under the strategy as a result of factsheets, presentations at grower meetings and on-farm demonstrations.

Through this strategy, the PRR is also providing collaboration opportunities and promoting new partnerships among various stakeholders, including growers, weed and crop experts, government research scientists, and the processing industry. Working together and engaging growers in such work increases the likelihood that the tools and practices developed through this strategy will be adopted and that risk reduction goals will be achieved.