Canola (Brassica napus L.) seedbank declines rapidly in farmer-managed fields in South Australia

Canola is an important crop in southern Australia, where it is used as part of the crop rotation to manage cereal diseases, improve wheat yields, and assist in integrated weed management programs. The potential release of herbicide-tolerant transgenic cultivars into Australia has raised concerns that volunteer canola may itself become an uncontrollable weed. This study examined the persistence of the canola seedbank in farmer-managed fields in 3 geographical areas of the South Australian cropping region for up to 3.5 years after the last canola crop was grown. In total, 66 fields from minimum- and no-tillage farms were sampled for number of canola seed/m2 and the percentage of those that germinated. ANOVA analysis indicated that time since the last harvest and cultivation method were both significant factors affecting the number of seed/m2 present. Neither time since harvest nor cultivation method was significant for number of germinated canola seeds, although time since harvest approached significance at the 5% level. This demonstrates that the canola seedbank and the number of volunteers decline rapidly in managed cropping systems in southern Australia. Therefore, it is unlikely that herbicide-tolerant canola will become a major weed if volunteers are managed carefully.