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Row covers as physical barriers in brassica vegetable crops to control cabbage maggot

Project code: PRR10-220

Project Lead

Josée Owen - Agriculture and Agri-Food Canada


  1. Identify commercial row covers that could serve as physical barriers in Brassica crops for cabbage maggot management.
  2. Field test the row covers for efficacy under conditions typical to local commercial production.

Summary of Results


Brassicaceae crops in all production regions in Canada suffer from losses attributed to the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae) and other closely-related species. Two organophosphates (chlorpyrifos and diazinon) are currently available to control these pests, however both are under re-evaluation by Health Canada's Pest Management Regulatory Agency (PMRA). In addition, research has confirmed that resistance to chlorpyrifos is spreading within cabbage maggot populations in British Columbia. Stakeholder consultations undertaken at a national level by Pesticide Risk Reduction (PRR) have identified the need for reduced risk alternatives to replace organophosphates. The goal was to develop reduced-risk cabbage maggot management tools which may ultimately be combined into an integrated approach to manage the pest in these crops. The investigation of the use of physical barriers is one of the actions being supported within the PRR’s cabbage maggot strategy.

Row covers made of netting are used in many European countries for cabbage maggot control in various brassica crops. They are considered a very effective tool if used properly; however, their use may lead to other pest management challenges, particularly adequate weed control. This project aimed to evaluate the effectiveness of commercially-available netting-style row covers as physical barriers in brassica vegetable crops, with the goal of reducing access of female cabbage maggot flies to their oviposition sites.


A field trial was conducted on rutabaga at multiple sites across New Brunswick, Newfoundland, Nova Scotia, and Prince Edward Island during 2011, to determine the efficacy of row covers to control cabbage maggot. Two types of commercially-available row covers were tested, Wondermesh® and ProtekNet®, both manufactured in Europe. In 2012, a second field trial was conducted in the above provinces to determine the efficacy of the same row covers when used in conjunction with different weed control treatments. The trial included the use of pre-emergent herbicides (Treflan EC, Bonanza L, or Devrinol 50 DF), a post-emergent herbicide (Lontrel 360), mechanical weeding, stale seedbed technique and combinations of these treatments along with row covers. All were compared with the commercial standard which included the use of chlorpyrifos sprays, a pre-emergent herbicide and mechanical weeding. A third row cover product, Crop Solutions®, was also tested in 2012 in Newfoundland and Labrador only.

Rutabaga was direct-seeded in field sites with a known history of pest pressure. The row cover treatments were applied within the week following seeding. In 2011, the sites were monitored for the presence of adult cabbage maggot flies. In 2012, the sites were monitored for the presence of adult cabbage maggot flies as well as weed occurrence, including biomass and dominant weed species. At harvest, rutabagas from each treatment were assessed for yield and cabbage maggot damage to determine the efficacy of the covers under the conditions of the season.


Results of this study indicated that the row covers provided an adequate barrier against cabbage maggot, achieving levels of protection that were similar to, or higher than, the commercial standard (chlorpyrifos). The different brands of row covers were comparable in all measured parameters. There was no negative impact of any of the row covers on crop yield.

In fields with low to moderate weed populations, a pre-emergent herbicide used with either mechanical weeding (by temporarily removing the row cover), or spraying post-emergent herbicide through the row cover could be used to control weeds. However, for acceptable efficacy, these measures needed to be timed correctly, both with respect to weed growth and to cabbage maggot adult fly populations (especially when temporarily removing the covers). Fields with high weed populations still represent a challenge and more research is needed to determine the most effective weed management strategy to use in conjunction with the row covers. Depending on the weed infestation levels in a field and the types of dominant weed species present, certain weed management strategies may be more effective in certain areas than in others.

Outreach, in the form of demonstrations, presentations and publications has been performed continually throughout this project. An economic analysis took into consideration the durability of the covers and their potential re-use for several years. The study indicated that while the covers carry a significant initial expense, they can still be a viable option for many growers because they can be used repeatedly for many years.

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