Reduced-Risk Strategy for Cabbage Maggot Management in Brassica Crops

For inquiries please contact:
Pest Management Centre, Agriculture and Agri-Food Canada (AAFC)
pmc.cla.info@agr.gc.ca

March 2017

Preface

Pesticide risk reduction strategies are developed under the Pesticide Risk Reduction Program (PRRP), a joint initiative of Agriculture and Agri-Food Canada (AAFC) and the Pest Management Regulatory Agency (PMRA) of Health Canada. The key objective of the program is to reduce the risks to the environment and to human health from pesticide use in agriculture. To achieve this objective, the Program works with grower groups, industry, provinces, and researchers to identify gaps in pest management and opportunities for pesticide risk reduction, and to develop and implement strategies to address these.

A pesticide risk reduction strategy is a detailed plan developed through consultation with stakeholders aiming to address growers’ needs for reduced-risk management tools and practices for specific pest issues. The strategy document presented herein is intended to update participating stakeholders on the activities supported by the Program in developing and implementing the strategy and new tools and practices made available through this process. Similarly, it is used as a reference document for the AAFC staff. The strategy also provides a baseline and enables tracking of advancements in pesticide risk reduction.

For more information on the activities and outcomes of the Program’s strategy work to date, visit the Pest Management Centre website www.agr.gc.ca/pmc.

Acknowledgement

The Pesticide Risk Reduction Program acknowledges all participating stakeholders, including members of the Cabbage Maggot Working Group, for their contribution and continued collaboration in the development and implementation of a reduced-risk strategy for cabbage maggot management in Brassica crops.

Introduction

Under the Pesticide Risk Reduction Program, efforts are being made to address pest management and pesticide risk reduction issues related to cabbage maggot, Delia radicum (L.), in Brassica crops. This issue was initially identified through a gap analysis of information, and the national Crop Profile for Brassica Vegetables in Canada developed and published by the Program, indicates that it remains a serious problem with limited management options. As the cabbage maggot is identified as a major pest of all Cole crops, this reduced-risk strategy covers the entire group of Brassica vegetables.

Pest management and pesticide risk reduction issues

The cabbage maggot, Delia radicum (Diptera: Anthomyiidae), is one of the most chronic and challenging pests attacking Brassica vegetable crops in Canada. The damage is caused by the larval stages. In cabbage, broccoli, cauliflower, Brussels sprouts, and other Cole crops, the larvae feed on seedling roots, decreasing vigour of the plants, and leaving them susceptible to infection by secondary soil-borne pathogens. In rutabaga, in addition to damaging the seedlings, larvae feed and tunnel into the developing roots, damaging the marketable product.

Pupation takes place in the soil. In the fall, the pupa becomes the overwintering stage. Adult flies emerge the next spring and resemble the house fly in their appearance. After mating they lay eggs below the soil surface near the plants. The adults are characterized by a low flying habit and typical spring infestation is caused by flies arriving from adjacent fields.

The cabbage maggot has 1 to 3 generations per year, depending on region and temperature. In Alberta, for example, it completes only one generation but there will be two peaks of flying adults: the first one in the spring and the second one later in the summer, as the first generation completes its life cycle.

In cabbage and broccoli, only the first generation is considered economically damaging as the plants have a good tolerance once they develop 4 to 5 true leaves. In rutabaga, damage by the second or third generation is considered significant as even a slight tunnelling into the developed root renders the crop unmarketable.

Conventional control of cabbage maggot relies on the application of chemical insecticides. Currently three insecticide chemical families are registered for use against the pest: formulations of cypermethrin (Group 3 insecticide) are registered in British Columbia for suppression of root maggot flies in rutabaga and turnip; a formulation of cyantraniliprole (Group 28 insecticide) is registered nationally to control root maggot in root vegetables and in Brassica vegetables, and formulations of the organophosphate chlorpyrifos (Group 1 insecticide) are registered nationally to control the maggots in rutabaga, pak choi, broccoli, Brussels sprouts, cabbages and cauliflower. When this strategy was initiated, growers relied heavily on chlorpyrifos; insect resistance to chlorpyrifos, however, is increasing. In 2013, 75% of populations tested in British Columbia were found to be chlorpyrifos-resistant.

Cabbage Maggot Working Group

The Cabbage Maggot Working Group was established in 2009 with the participation of commodity experts, pest management researchers, and stakeholders of the Brassica crops industry across the growing regions. The group has been working on the development and implementation of a pesticide risk reduction strategy, with emphasis on the prioritization of potential solutions and research needs. Discussions to develop the strategy took place by phone calls, email correspondence, teleconferences, and face-to-face meetings. Some members of the Working Group are also collaborators in various projects put in place to implement the strategy.

Priority issues and gaps

The following key issues and gaps were identified through discussions with the Working Group:

Goal 1: Establish knowledge base on management approaches

  • Need to establish ‘knowledge base’ on management approaches of cabbage maggot from around the world
  • Need to address the lack of knowledge on the prevalence of Delia species in Brassica growing areas in Canada
  • The sensitivity Delia species to chlorpyrifos is largely unknown. This should be tested in as many Brassica growing areas as possible
  • There is lack of knowledge about the possibility of controlling cabbage maggot adult flies by attract-and-kill technology
  • Need to communicate knowledge about effective new technologies to growers and stakeholders

Goal 2: Develop physical barriers for cabbage maggot management

  • Need to continue the development of exclusion fence and assess its efficacy as a physical barrier to prevent cabbage maggot flies from entering the field
  • Need to test various materials applied to the soil that may be suitable for use as physical barriers to prevent cabbage maggot female flies from reaching their oviposition sites
  • Need to evaluate whether European technologies of insect netting could be suitable as physical barriers against cabbage maggot adult flies under Canadian conditions. Where found efficacious and economically-feasible, need to develop best practices for their use

Goal 3: Develop rutabaga lines resistant to cabbage maggot

  • Need to continue the breeding of rutabaga to develop commercial-grade lines resistant to cabbage maggot

Goal 4: Evaluate potential for biopesticides as cabbage maggot management option

  • Need to test biopesticide candidates and determine their potential use for management of cabbage maggot

Strategy Action Plan

Four strategy goals related to reduced risk cabbage maggot management, and potential solutions prioritized through stakeholder consultations and by the working group led to the development of a pesticide risk reduction strategy action plan for cabbage maggot in Brassica crops. The plan is centered on obtaining lower risk control tools and practices that reduce reliance on insecticides while offering effective, economically-feasible pest management options. The table below outlines the goals, the milestones and the implementation activities completed or underway in support of this strategy.

Action plan table including goals, milestones and activities for implementing the reduced-risk strategy for cabbage maggot management in brassica crops in Canada

Goal 1: Establish knowledge base on management approaches
Milestone Status Implementation Activities Completion date
Literature survey of available pest management approaches Complete AAFC’s project PRR06-690: Cabbage maggot management and research around the world: a status report and development of IPM strategies for Canada. Information obtained through published sources and discussions with leading experts revealed national and regional differences in the approach to Delia management, which vary with the type of crop (canola/vegetables), damage (direct vs. indirect), scale (farm/field size) and production system (organic vs. conventional). As no single available method provides full control of the pest, the development of several management tools under an integrated approach will be necessary to control infestations in a sustainable manner. March 31, 2007
Examine prevalence of Delia species and their sensitivity to chlorpyrifos Ongoing AAFC’s project PRR15-020: Species survey and testing of resistance to chlorpyrifos in Delia species in brassica vegetable growing areas in Canada. The project is surveying species of Delia flies in vegetable Brassica crops across Canada, to determine which of them causes damage to the crops, and assess the level of resistance to chlorpyrifos in these populations. March 31, 2017
Explore the possibility of controlling cabbage maggot adult flies by Attract-and-kill technology Future This approach is currently considered low priority by the Working Group. Studies undertaken outside this strategy may help determine whether this is a viable option to control the pest.  

 

Goal 2: Develop physical barriers for cabbage maggot management
Milestone Status Implementation Activities Completion date
Assess the efficacy of exclusion fence as a barrier to prevent cabbage maggot flies from entering the field   Complete AAFC’s project PRR09-050: Development and demonstration of a multi-tactical IPM toolbox for cabbage maggot control in Brassica crops. The project included a commercial-grade exclusion fence developed with industry and demonstrated to growers in various research and commercial sites. The project identified issues and developed recommendations for the optimal use of this technology. March 31, 2012
Communicate the technology of exclusion fence to stakeholders Complete A factsheet titled Exclusion fence technique for cabbage maggot management in Brassica vegetable crops was developed and posted on AAFC’s website. It presents the method and provides criteria for the selection of fields where this technology may be implemented.  December 14, 2015
Test physical barriers applied to the soil as barriers against cabbage maggot adult flies seeking oviposition sites Complete AAFC’s project PRR10-170: Physical barriers to control cabbage maggot (Delia radicum L.) in brassica vegetable crops. Various types of barriers including liquid and biodegradable mulches, diatomaceous earth, and kaolin clay, were tested. None was found to provide sufficient protection under the conditions assessed. March 31, 2012
Test commercial row covers (‘insect netting’) as barriers against cabbage maggot adult flies seeking oviposition sites. Identify issues and develop recommendations for the use of this technology. Complete AAFC’s project PRR10-220: Row covers as physical barriers in Brassica crops for cabbage maggot management. Conducted in the Atlantic provinces, the technology was found effective in protecting the crop at a similar level to – or better than – conventional insecticides. In some rutabaga fields, weeds are problematic when using row covers. March 31, 2013
Test commercial row covers (‘insect netting’) as barriers against cabbage maggot adult flies seeking oviposition sites. Identify issues and develop recommendations for the use of this technology. Complete AAFC’s project PRR14-010: Evaluating row covers for early season management of cabbage maggot in brassica vegetable crops. Work to establish best management practices for early-season control of cabbage maggot was conducted in the Atlantic provinces and British Columbia. The project studied conditions under the nets and assessed equipment for the deployment and collection of the nets. Knowledge and Technology Transfer (KTT) activities introduced the technology to interested parties via field days, demonstration trials, growers’ meetings, and communication material. March 31, 2017
Communicate the technology of insect netting to stakeholders Ongoing  Numerous KTT activities were undertaken through project PRR14-010 (see above). Develop a factsheet to introduce the insect netting and include recommended practices for optimal use of this technology as a management tool for cabbage maggot.  
Goal 3: Develop rutabaga lines resistant to cabbage maggot
Milestone Status Implementation Activities Completion date
Breeding to obtain BC-3 (third back-cross) generation resistant to cabbage maggot Complete AAFC’s project PRR10-140: Development of rutabaga cultivars resistant to Cabbage maggot. The commercial cultivar Laurentian, bred to incorporate resistance to cabbage maggot is expected to be available by the end of this project. Breeding phase is complete, with three lines identified as candidates for commercialization based on their level of resistance and horticultural traits. August 31, 2016
Field-testing of resistant rutabaga lines Complete AAFC’s Project PRR12-110: Field testing rutabaga cultivars for resistance to cabbage maggot. Resistant rutabaga lines were field-tested in various rutabaga growing regions across Canada and assessed against the susceptible Laurentian cultivar (the lines were tested only in Ontario under project PRR10-140). March 31, 2017
Promote grower adoption of resistant cultivar Ongoing AAFC’s project PRR10-140: Development of rutabaga cultivars resistant to Cabbage maggot. If found effecacious in the field, information concerning the resistant lines will be communicated to growers, commercial seed producers, and other stakeholders. During 2017, the three lines identified as best candidates for commercialization will be evaluated by a commercial partner under agreement with the University of Guelph, the owner of the resistant lines.  
Goal 4: Evaluate potential for biopesticides as cabbage maggot management option
Milestone Status Implementation Activities Completion date
Laboratory testing of biopesticide candidates for management of cabbage maggot Complete AAFC’s project BPI08-010: Biological control of soil insect pests in field crops. Aimed at evaluating commercialized fungal biocontrol products for their suitability to control Delia species, the project tested eight different products in laboratory scale experiments and identified one Metarhizium based product as potential candidate for integration into IPM systems. March 31, 2011
Field testing of biopesticides to determine efficacy and suitability for use under Canadian cropping systems No longer a priority No further work in this direction is planned at this time. Potential expansion of the label of the Metarhizium -based product for use against cabbage maggot in Brassica crops is at the discretion of the registrant.  

Strategy Outcomes

The main outcomes expected from the implementation of the Reduced Risk Strategy for Cabbage Maggot Management include:

  • Knowledge on pest management approaches from around the world that could fit production systems of Brassica crops in Canada compiled and made available to interested parties
  • Exclusion fence developed, tested, and available for use as a physical barrier
  • European insect netting technologies evaluated, including nets and machinery. Best practices for using commercially-available nets and equipment identified and demonstrated to growers and other stakeholders
  • Resistant rutabaga lines developed, tested, and available for commercialization
  • Information about Delia species’ distribution and resistance to chlorpyrifos available
  • Communication material developed and disseminated
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