Soroka: Monitoring of Swede Midge Populations in Saskatchewan and Determining the Impact of Swede Midge on Different Growth Stages of Canola
Date: March 2017
Term: 3 years
Status: Completed
Researcher(s): Julie Soroka, Owen Olfert, Larry Grenkow, Lars Andreassen, Boyd Mori, Agriculture and Agri-Food Canada, Saskatoon SK
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
The swede midge, Contarinia nasturtii, is a significant pest of brassica vegetable crops and canola in eastern Canada. It was first discovered in Saskatchewan in 2007 where it now threatens the canola industry. Researchers initiated a three-year study to investigate the susceptibility of canola at different growth stages to infestation by swede midge, as well as the influence of seeding date and insecticide seed treatments on levels of infestation. Overall, the research shows that agronomic benefits of early seeding outweighs the effects of the midge damage; therefore producers should plant when conditions are most agronomically suitable. Seed treatment had no effect on midge damage.
The swede midge, Contarinia nasturtii, is a significant pest of brassica vegetable crops and canola in eastern Canada. It was first discovered in Saskatchewan in 2007 where it now threatens the canola industry. In Ontario, there are usually four generations annually; the number of generations on the Prairies is not known. Researchers set out to learn more about swede midge populations and control in Saskatchewan.
Researchers from Agriculture and Agri-Food Canada initiated a three-year study in 2014 at four sites in northeastern Saskatchewan near Ridgedale, Codette and Carrot River. The objectives of the study were to investigate the susceptibility of canola at different growth stages to infestation by swede midge and to determine the influence of seeding date and insecticide seed treatments on levels of infestation. Researchers also wanted to assess the effectiveness of swede midge adult sampling techniques (emergence and pheromone traps) throughout the summer to determine the phenology of swede midge populations.
The project was conducted on four commercial canola field sites in northeastern Saskatchewan, with each location setup in a split plot design. Canola was seeded at both early and late seeding dates across the whole plots, with four different seed treatments applied to subplots. The four experimental seed treatments included: fungicide alone, Helix Vibrance (439 g), Lumiderm (400 g), and Helix Vibrance plus Lumiderm (439 g and 400 g, respectively). The varieties used depended on the site, and were the same as the producer seeded in the rest of the field. Seedling emergence and flea beetle injury were rated for early and late seeded plots. Damage was rated weekly thereafter to the pod-fill stage. Plots were swathed, harvested, and seed yield per subplot was measured. Emergence cages and pheromone traps were also set up in the fields and regularly monitored starting in early May to determine the phenology of swede midge populations.
During the study, researchers discovered a second Contarinia midge species infesting canola that previously was unknown. Because researchers were unable to differentiate the damage caused by both species, any assessed damage was considered to be caused by the Contarinia midge complex (which includes both swede midge and the new Contarinia midge species).
Overall, the research found that damage caused by the Contarinia midge complex was extremely low over the three-year project. Generally, early seeded plots had higher injury ratings than late seeded plots; however, seed yield was not impacted. Seed treatment had no effect on midge damage and indicated either that the insecticides have dissipated and are no longer effective when midge attack, or midge damage is so low that no differences could be observed between all the seed treatments. Researchers would like to repeat the study in areas of high swede midge population levels such as those observed in Ontario.
Pheromone traps captured very few midges across all study years, which indicates swede midge is either present in extremely low population levels or not present at the study sites. The newly identified Contarinia midge is not attracted to swede midge pheromone, so in the future researchers hope to identify the pheromone from the new Contarinia midge in order to more accurately monitor population levels.
Emergence traps provided some initial data on the lifecycle of the new Contarinia midge species, which has at least two generations on the Prairies, with only one appearing at the time of canola susceptibility in the course of the study. Emergence traps also indicate that swede midge were not emerging from the soil at the four research sites. Future work is needed to elucidate where swede midge is present on the Canadian Prairies.
Overall, the research shows that agronomic benefits of early seeding most likely outweigh the effects of the midge damage observed; therefore, it is still imperative that producers plant when conditions are most agronomically suitable. Two parasitoid species were found to attack midge infested flowers. If these parasitoids are attacking swede midge, this is the first report of parasitism in North America.