Physical barriers applied to soil surface in the field and in the greenhouse to prevent oviposition by cabbage maggot

Project Code PRR10-170

Project Lead

Josée Owen  Agriculture and Agri-Food Canada

Objective 

  • Identify barriers that could potentially reduce access to oviposition sites by female cabbage maggot flies
  • Develop and test the application methodology and the efficacy under greenhouse and field conditions

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. 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. The goal is to develop tools which may ultimately be combined into an integrated approach to manage the pest in these crops with reduced reliance on organophosphate insecticides.

Approaches

During the growing season of 2010, a screening trial of potential physical barriers in rutabaga and cabbage was conducted in comparison with an untreated control and with the commercial standard Lorsban (active ingredient chlorpyrifos, an organophosphate insecticide). Treatments included SPLAT (a biologically inert matrix that is used for delivering pesticides and/or pheromones in horticultural cropping systems), FlexTerra (a biodegradable product that is used for erosion control), Hydro mulch (a biodegradable product that is used for erosion control), Tanglefoot glue (a sticky coating used in insect traps), AMP liquid mulch (a product made of cellulose and polymers that forms a cardboard-like film is used for weed control), Diatomaceous earth (a mineral, mined in areas of deposition of diatoms, that is used as an insect control product and soil conditioner), and Surround crop protectant (a product made of Kaolin clay that is used as a barrier to protect crops against certain insect pests).

Due to inconclusive results, a second screening trial was conducted on cabbage in the 2011 season. Treatments included AMP liquid mulch, Surround crop protectant, dolomitic lime (a soil amendment made from crushed limestone or chalk, with calcium carbonate as its primary component), paper mulch (a product similar to Kraft paper, which is used for weed suppression in organic gardening), and nonwoven bamboo batting (a product made of bamboo fibres). In addition to the standard treatment Lorsban, this year’s trial also tested Entrust biopesticide (active ingredient spinosad). In both years, all barriers were applied shortly after transplanting and reapplied where needed (e.g. Hydro mulch requires only one application whereas Surround requires repeated applications).

Efficacy of the different treatments was established by collecting data on plant mortality post-transplanting, durability of the barriers, and pest counts during the growing season (eggs and larvae). In 2010, harvest data were also collected and the crop was graded for damage caused by cabbage maggot. Unfortunately, late transplanting meant that yield data were unavailable in 2011 due to an unforeseen need to find a new trial location for the plots.

Results

While some treatments (primarily Surround crop protectant) had reduced populations of cabbage maggot eggs and larvae in the soil nearby the roots, as well as reduced damage in the harvested crop (where recorded), none of the barriers provided protection at a level that may be considered commercially acceptable. The barriers also didn’t appear to have season-long durability in rutabaga, with the roots detached from the barriers and became exposed to female flies as they swelled. Statistically, the physical barriers gave the same level of control as the commercial standard Lorsban, which by itself did not differ significantly from the untreated check. This may suggest that resistance to chlorpyrifos is spreading among cabbage maggot populations in Atlantic Canada.

The concept of preventing access to host plants as a mean of managing cabbage maggot in brassica crops is gaining support among researchers, specialists and growers alike. It appears, however, that available technologies are effective when applied around the field (exclusion fence) or over the rows (mesh covers) while materials that may be used as barriers on the individual plant require further study. Those that were tested in the current project, and by the current methods of application, do not seem promising for that purpose.

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