Analysis of the data from trials conducted on grower fields in 2013-2015 has helped to elucidate the relationship between swede midge pressure (as represented by captures of male midges in pheromone traps) and yield. Results also suggest that the number of midges associated with a 10% yield loss differed among plant stages, and that a lower action threshold should be used from emergence to the fourth leaf stage than for later plant stages.
PURPOSE: Swede midge is an invasive fly that has become one of the most important pest species for canola growers in Ontario, since its discovery in 2000. The first record of swede midge in the Prairies was made in 2007 and since then swede midge has spread widely across Saskatchewan and Manitoba. Controlling swede midge can be challenging due to the cryptic feeding habits of damage-causing larvae, their short residency on host plants, and the delayed onset of damage symptoms. Canola crops can experience high pressure throughout the growing season due to the four overlapping generations of swede midge in Ontario. Swede midge feed on young, fast growing tissue, meaning that canola is susceptible to damage through several growth stages. Prior research suggests there are several key growth stages of canola most susceptible to swede midge infestation. Therefore, using canola growth stage to time insecticide applications may be an effective method for reducing damage by swede midge larvae. Due to their short residency on host plants, further refinement of insecticide application timing could result in greater larval mortality. Defining the relationship between the timing of adult swede midge captures on pheromone monitoring traps and the presence of the resulting offspring of those adults could improve efficacy and efficiency of insecticide applications for the control of swede midge in canola.
OBJECTIVES: This activity will contribute to the development of effective integrated pest management practices for swede midge in canola through the following specific objectives:
- To evaluate insecticide efficacy and timing of insecticide applications for reducing swede midge damage in spring canola.
- To evaluate the use of pheromone-based action thresholds in determining the timing of insecticide applications against the swede midge.
- To develop decision-making protocols for the timing of insecticide applications against the swede midge, based on crop stage and/or pheromone-based action thresholds.
RESULTS: The following conclusions were also determined:
- Trap captures of ~9 midges/trap/day can be associated with 10% yield losses during the early vegetative stages.
- Trap captures as low as 3-4 midges/trap/day can be associated with 10% yield losses during the early bud and first flower stages.
- It takes two to three times higher daily trap captures of swede midge to cause 10% yield losses during the late vegetative to early bud stages.
- Trap captures best predict damage 10 days later.
- Trap captures best predict egg and larval numbers 3-4 days later.
- Lambda-cyhalothrin, but not chlorantraniliprole, is effective at preventing yield losses by swede midge.
- When applied during the late vegetative stage (seven to nine leaf stage), or when applied during both the early vegetative (one to three leaf stages) and late vegetative stages, lambda-cyhalothrin can increase canola yield between 177 – 189 kg/ha.
- There is a second Contarinia species affecting canola on the Prairies.
- Variability in swede midge pressure, in canola response to swede midge damage, and the ability of canola to compensate, at least to some extent, for swede midge damage and compensation results in variability of results in swede midge field trials. We have found that pooling analyses of trials over multiple years and locations provides insights into the relationships between swede midge numbers and canola yield losses, which are often difficult to elucidate in analyses of single trials.