Canola (Brassica napus) hybrids and higher crop seeding rate contribute to reducing annual ryegrass (Lolium rigidum) and wild radish (Raphanus raphanistrum) growth and seed production

Context Canola (Brassica napus L.) production is highly dependent on herbicides, but agronomic practices that increase crop competitiveness may improve weed suppression and reduce reliance on herbicide-only weed control. Aims This study tested whether hybrid canola, increased crop density and narrower row spacing improve suppression of annual ryegrass (Lolium rigidum Gaudin.) and wild radish (Raphanus raphanistrum L.) compared with open-pollinated canola grown at lower densities and wider row spacing. Methods Seven field trials were conducted in Western Australia from 2018 to 2020. Two triazine-tolerant canola cultivars, hybrid HyTTec® Trophy and open-pollinated ATR Bonito™, were evaluated at target densities of 20, 35 and 50 plants m−2, equivalent to 0.4, 0.7 and 1.0 times the recommended seeding rate, and at row spacings of 0.25 and 0.50 m. Key results Hybrid canola tended to reduce weed biomass and seed production compared with open-pollinated canola, decreasing annual ryegrass and wild radish biomass by approximately 9% and 17% respectively. Increasing crop density consistently reduced weed biomass and seed production, with 30% and 50% less seed for annual ryegrass and wild radish respectively. Wider row spacing generally increased weed seed production, although responses varied among environments and were not significant overall. Conclusions Hybrid canola cultivars and increased crop density improved crop competitiveness and weed suppression across contrasting Western Australian environments. Implications Selecting competitive hybrid cultivars and maintaining higher crop densities can strengthen integrated weed management in canola and complement herbicide-based weed control strategies.