Project Code: PRR09-050
Project Lead
Bob Vernon - Agriculture and Agri-Food Canada
Objective
To evaluate and demonstrate the efficacy of exclusion fences in managing cabbage maggot in commercial rutabaga crops
Summary of Results
Background
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 confirmed that resistance to chlorpyrifos is spreading within cabbage maggot populations in British Columbia (BC). The investigation of the use of physical barriers is one of the actions being supported within the context of a Reduced-Risk Strategy for Cabbage Maggot Management in Brassica Crops. The goal is to develop tools which may ultimately be combined into an integrated approach to manage the pest in these crops in an environmentally sustainable manner.
Approaches
The project facilitated the development, testing and demonstration of exclusion fences as an alternative method for cabbage maggot management. A prototype of the fence was developed in 2009. It consisted of black, 1 millimeter mesh nylon window screen attached to aluminium rails at 2.5 meter (m) intervals. The height of the fence was 1.3 m. In line with each rail was an additional 0.3 m length of rail as an overhang brace, bent downward at a 45 degree angle and facing outside the field. A nylon rope running between the rails served to keep the fence material straight along the top of the rails. At ground level there was about 0.2 m of excess screen laid flat on the surface inside the field and covered with soil. The screen plus rail assembly can be rolled up for storage over the winter, and estimates are that under optimal conditions it may be used repeatedly for about ten years.
In the first year (2009), demonstration trials took place in two rutabaga fields in Delta, BC, and were compared with two unfenced fields. Plot sizes were between 1.4-6.2 hectare (ha).
In 2010 three fenced rutabaga fields (1.4 to 4.1 ha) were compared with an unfenced field of 2.2 ha in Delta, BC. One of these trials involved a new Agriculture and Agri-Food Canada (AAFC) developed commercial fence design, Telstar Eco Fence, thus the project encompassed a prototype development as well as development and demonstration of a commercial fence, including the development of an illustrated manual to facilitate transfer of the technology to growers. This new model was also evaluated on a smaller scale by collaborators in Saskatchewan and Newfoundland in 2010 and 2011.
Results
In 2009, data showed that numbers of cabbage maggot adults, egg deposition and damage to rutabaga plants were reduced in the fenced plots when compared with the unfenced ones. Pest populations and crop damage were aggregated along the crop perimeter inside the fence, in a corridor up to 13 m wide. The data suggested that exclusion fences may be used in fields larger than 1 ha as a first line of defense against cabbage maggot. The data also indicated that other control methods should be combined with the fence technology to reduce the accumulation of pests and crop losses along the perimeter.
In 2010, damage levels and pest populations within the fenced fields were higher as more flies were able to defeat the fence. Spatial distribution indicated a similar pattern to 2009, with the highest numbers of flies, eggs, and crop losses occurred in rutabaga rows closer to the fence. As fields selected in 2010 were different than in 2009, these trials enabled to collect information and identify the factors that reduce the efficacy of the fence as a pest management tool.
In 2011, the commercial model of the fence was tested in BC, Saskatchewan (SK) and Newfoundland (NL). In terms of labour and expertise, the fence was found to be relatively simple to erect and dismantle. In terms of durability, the fence appeared to be susceptible to high winds that cause tearing to the mesh, which, in turn, create more opportunities for the flies to cross the barrier and also reduce the expected lifespan of the fence. The level of protection provided by the fence was inferior when compared with the standard chemical insecticide, but greater than the untreated, unfenced plots.
Exclusion of female cabbage maggot was achieved to varying degrees in BC, SK, NFL over the three years of the project. The work conducted in this project served to elucidate some of the important aspects of field selection which can impact the successful implementation of the exclusion fence approach to cabbage maggot management. The variation seen in exclusion of flies at different sites and in different years serves to underscore the importance or respecting criteria related to selection of fields.
Pre-requisite conditions for field selection include:
- Low surrounding topography – avoid slopes or high grounds around the field, as they enable the flies to hover above the fence and fly into the field
- Minimum plant growth external to the fence – weeds and other plants outside the field should be removed or maintained at low height so as not to affect the flight pattern of the flies (they tend to fly above high vegetation and into the field)
- Fields with low in-field cruciferous weed populations, since these can be alternative hosts and potential sources of re-infestation
- Pest pressure has to be low to moderate. In high pest pressure the fence is less effective as the population of flies that defeat the fence is proportionally high, causing an increase in crop damage
- Previous-year crops should be non-host plants. If cruciferous crops (or weeds) were in the field the previous year, overwintering pupae of cabbage maggot are already in the soil, giving rise to the fly population inside the fenced area
- Timing of fence erection must be before the planting of the brassica crop or shortly thereafter
- Field shape – square plots are preferable to plots that are long and narrow, where much of the field area is within the susceptible corridor along the fence
A pictorial instruction booklet for installation of the commercial model has been completed in English and French and is useful in facilitating the transfer of this technology. Field days were held in 2009 and 2010 in Delta, BC, to demonstrate the technology to the grower community. As well, two papers were presented in 2009, two paper proceedings were published in 2011 from an IOBC (International Organization for Biological Control) meeting in Dubrovnik, Croatia, and several other publications and seminars have communicated the results of this project.
The Telstar Eco Fence was similar in cost to the prototype of 2009 but easier to install and dismantle. A detailed analysis of costs associated with the manufacturing, installation, maintenance and dismantling of the fence was carried out as part of this project. This analysis indicates that in large scale production situations the fence can be a cost effective approach to a first line of defence against cabbage maggot. In addition, information gathered about the spatial distribution of the females which defeat the fence could be useful in designing a strategy to destroy the insects congregating in a band along the interior of the fence. As such, the exclusion fence could be one tool within an integrated pest management (IPM) approach to reduced-risk cabbage maggot management.
For more information, please contact Bob Vernon of AAFC, Agassiz, BC.