Evaluation of selected commercial oilseed rape cultivars for early vigour, weed suppression and yield in southern New South Wales

Abstract The potential of oilseed rape to suppress weed growth while maintaining optimal yield and quality is not well understood under field conditions in Australia. This study, conducted in Condobolin and Wagga Wagga, New South Wales (NSW), during 2015 and 2016, examined a diverse range of commercial oilseed rape cultivars for their inherent ability to suppress weeds and maintain yields when in competition with natural weed infestations, with and without pre‐emergent herbicide treatment. Cultivar differences were observed in oilseed rape canopy architecture and yield; however, early‐season biomass, light interception, leaf area index and visual vigour ratings exhibited both year and location interactions. Cultivars with the highest biomass, light interception, leaf area indices and visual vigour were typically also the most weed‐suppressive, in particular GT‐50 and Hyola 600RR. Although crop and weed biomass accumulation differed significantly among cultivars for both location and year, weed biomass was inversely related to cultivar biomass in both years and locations. Hybrid Hyola and GT‐50 cultivars exhibited up to 50% less weed biomass while maintaining consistently high levels of dry crop biomass. In addition, pre‐emergent herbicide applications reduced weed infestation and contributed to higher crop yield in both locations and years. Given the consistent aboveground competitive ability of certain oilseed rape cultivars, our study demonstrated that diverse cultivar‐dependent competitive traits such as early growth vigour, biomass production, absorption of photosynthetically active radiation and production and retention of crop residue significantly impacted weed establishment and total weed biomass. Our findings suggest that cultivar selection offers potential as a tool for maintaining suitable grain yield in the presence of weeds while potentially delaying the development of herbicide resistance through efficacious weed suppression.