To enhance seed treatment effectiveness, seed canola should be placed into warm soil (5 °C or higher). The proper depth of seed should be 1–2 cm to ensure rapid emergence (Canola Council of Canada (2007)). Plants were seeded 0.635 cm in depth in this study, because in the Golden Triangle area,

soil temperature in May ranged from 1 to 4 °C, and the soil was hard when the canola was seeded. The cool soil temperature, combined with the shallow sowing, was likely to have prolonged the time required for the crop to grow beyond the vulnerable early-seedling stage. Roxadustat If canola germinates but stays below ground for 14 days or longer before emerging due to cool soil, the likelihood that seed treatment protection will diminish before the canola crop advances beyond the 4-leaf stage is greatly increased (Canola Council of Canada (2007)). Another factor which may contribute to the low effectiveness of seed treatment in our experiment was that the rate of insecticide used for seed treatment was too low. Knodel et al. (2008)

demonstrated that flea beetle (Phyllotreta spp.) injury ratings declined when a high rate of insecticide for seed treatment was used. From their experiment, the rate of 8 g/1 kg of imidacloprid seed treatment lowered the P. cruciferae damage significantly compared to the rate of 4 g/1 kg of seeds. Seed treatments BGB324 order typically have an Sinomenine effective residue of 21 days against P. cruciferae feeding

injury ( Knodel and Olson, 2002). Because of that, the canola crop might be vulnerable when crop emergence or growth is delayed or peak emergence and invasion of flea beetles are later than the 21 days window of protection ( Knodel et al., 2008). However, our study was in agreement with Knodel et al. (2008) and Dosdall and Stevenson (2005), in which less flea beetle damage was found on plants treated with insecticide seed treatment than on plants without an insecticide seed treatment. Our study showed that a calendar-based program at 15-day intervals resulted in significantly higher yields compared to other treatments, except for the threshold-based spray at 15–20% leaf damage (Fig. 1). Interestingly, this calendar-based program (15-day interval) had significantly more leaf damage than 15–20% threshold-based treatment though not a significantly greater yield. This may be explained by various factors. For example, the canola plants in plots treated on a calendar based might have had better ability to outgrow damage by P. cruciferae after bolting than plots treated based on threshold levels. In general, however, a negative correlation was indicated between yield level and leaf damage ( Fig. 2). On the other hand, Trdan et al. (2005) reported that statistically significant and positive correlation between leaf damage and number of flea beetles (Phyllotreta spp.) on white and Chinese cabbage.