Varietal differences in response to imidacloprid seed treatment in germination and early seedling growth of oilseed rape

Phytophagous insects of Brassica napus may be controlled by imidacloprid seed coating, but the treatment may have risks as well as benefits. In this study, seeds of several elite B. napus cultivars were coated with imidacloprid at four concentrations (150, 300, 600 and 1200 mg AI (active ingredient) L-1) and/or for different exposure periods, and seed germination and early seedling growth evaluated. Imidacloprid seed coating inhibited germination and early seedling growth, an effect that increased with increase in concentration and exposure time, and that weakened as the plants grew. The inhibitory level varied between the cultivars. According to the inhibition level of germination, the tested cultivars could be grouped into three categories: the most tolerant, the most susceptible and the intermediately-tolerant cultivars. If the cultivars are the most tolerant, high imidacloprid concentration could be implemented without causing significant reduction in germination and seedling growth. However, it would be infeasible to coat the most susceptible cultivars with imidacloprid at high concentrations, due to more than 80% germination loss and unrecoverable inhibition of seedling growth. Therefore, before seed coating is commercially adopted, cultivars should be screened for their sensitivity to imidacloprid.