Integrated approaches for flea beetle control II: Incorporating the impacts of plant density, ground predators, and landscape-scale predictive models in the management of flea beetles in the Canadian Prairies

Project Summary

Purpose: 

Flea beetles are one of the major pests of canola in Western Canada. Canola growers need strategies to improve the efficiency of seed treatments, and flea beetle management in general. This study will address research gaps that could improve flea beetle management. These include the effect of plant density in flea beetle management, the effect of stem feeding damage on the flea beetle control, the role of natural enemies on flea beetle management, and regional predictive models for flea beetle abundance. This study builds on the outcomes of the ‘Integrated approaches for flea beetle control – economic thresholds, prediction models, landscape effects, and natural enemies‘ project.

Project objectives:

• Evaluate the effects of different seeding rates and insect management options on the economic thresholds for flea beetles using current canola cultivars.
• Evaluate the effects of different seeding rates of canola on flea beetles infestations under field conditions.
• Evaluate the effect and the mechanism of stem feeding by different flea beetle species under laboratory and field conditions; determine the direct and indirect effects of predators on stem damage and defoliation.
• Determine the effect of ground and foliar predators and landscape structure on canola defoliation, flea beetle abundance, and species composition in different regions of Western Canada.
• Construct a predictive model for flea beetle abundance and damage to canola, incorporating predators, landscape effects, and abiotic factors.

Field trials

Between 2018 and 2022, researchers conducted 16 trials in Manitoba, Saskatchewan, Alberta-Peace River and Alberta- Lethbridge. Treatments were a combination of different seeding rates and flea beetle control methods. Seeding rates were low (3.5 kg/ha or 3 plants per square foot), optimum (7 kg/ha or 6 plants per square foot) and high (14 kg/ha or 12 plants per square foot).

Flea beetle control methods included fungicide-only treated seeds (i.e. control), insecticide and fungicide-treated seeds (i.e. seed), foliar insecticide spray at 25 per cent defoliation with fungicide-only treated seeds (i.e. foliar) and a weekly foliar insecticide spray with fungicide-only treated seeds (i.e. FB-free).

Results

The seed treatments were more effective in reducing flea beetle
defoliation than the foliar spray, which provided intermediate
control compared to untreated plots.

• The FB-free treatment indicated that foliar and seed treatments did not completely prevent damage in Manitoba and Saskatchewan.
• Seeding rate had no effects on defoliation of the control, foliar and FB-free treatments, whereas increasing the seeding rate decreased canola defoliation for treated seeds.
• For all treatments, low-seeded plots were less attractive to flea beetles than high-seeded plots. The optimum-seeded plots had an intermediate effect in the control and foliar treatments.
• Higher seeding rates resulted in a lower number of flea beetles per plant (as the total number of beetles can disperse onto fewer numbers per plant when more plants are available). The optimum seeding rate had intermediate levels of flea beetles per plant in Manitoba and Peace River, while Lethbridge had higher and Saskatchewan had lower levels.
• Though no economic analysis was incorporated, higher seeding rates resulted in better yield, regardless of flea beetle control methods and across all regions.
• Less whole-plant damage occurred when ground beetles and spiders were present. In addition to eating flea beetles, the reduction in stem damage without a reduction in cotyledon damage prevalence may suggest a behavioral change of flea beetles moving up the plant to avoid predation.
• Both striped and crucifer flea beetles increased damaging activity with warmer temperatures, causing the most cotyledon damage at 28oC. Both species also damaged the underside of the cotyledon more than the upper side. There was no difference in amounts of damage between species.
• Large canola crops favoured flea beetle abundances at the field scale, but fields located in landscapes with higher proportion of non-canola crops showed lower infestation levels. Grass borders at large scales appeared to favour flea beetle abundances potentially by providing overwintering/dispersing sites, however, the opposite effect was observed at smaller scales. Higher edge density (indicating smaller fields and habitats in the landscape) and more woody habitats helped against flea beetle infestations most likely by acting as physical barriers against flea beetle movement and dispersal to canola.