Manipulating canola agronomy for weed suppression

Weed control options in canola have improved considerably with the development of a range of herbicide–tolerant (HT) cultivars. However, the widespread incidence of weed resistance to many herbicide groups requires the inclusion of non-chemical control tactics in management strategies. Volunteer cereals can also significantly impact on canola yields. Competitive crops can reduce weed costs, and also increase the efficacy of currently-effective herbicides. Studies in 2009, examined the range in competiveness available in 15 current diverse canola types with annual ryegrass (Lolium rigidum Gaud.). Significant differences in grain yield of canola were
recorded in weedy and weed-free plots, with percentage yield reductions from weeds of 60-100%. The hybrids were higher yielding and were more competitive than the open-pollinated cultivars, and especially the triazine–tolerant ones. Higher crop seeding rates improved the competitive ability of two of the diverse canola genotypes against volunteer wheat, especially in more weakly competitive genotypes compared to stronger competitors. The role of crop competition, as influenced by choice of genotype and seed rate, is discussed as an important
low cost component of integrated weed management systems to reduce dependence on herbicides, improve performance of HT cultivars, and retard resistance spread in weed species.