Some growers are looking at tighter rotations for this year, seeding canola on fields that were in canola two years ago or, in some cases, last year. This is not a best practice for well-known reasons of disease build up and lower yields. In Manitoba, for example, canola on canola stubble yields 83% of the average canola yield for the province, according to Manitoba crop insurance data. Canola on canola also raises the issue of volunteer canola control. Growers who choose to seed canola on canola should rotate herbicide-tolerance systems on that field. For example, if they seeded Roundup Ready canola two years ago, this year use a different system on that field. This provides an important opportunity for post-emergent volunteer control, especially if growers missed an opportunity to apply CleanStart (the only pre-seed burnoff registered to control Roundup Ready volunteers) before seeding.
Volunteer Roundup Ready canola is not a benefit in a Roundup Ready crop. Volunteers are often in clusters, particularly in strips where the windrows were the fall before. That means elevated plant counts in those strips, which lead to lodging and sclerotinia infestation. Volunteers are also usually at different stages than the crop, which makes it difficult to time disease control and harvest. And volunteer seed is untreated, so it can contribute to the build up of seed and seedling diseases in the soil. Volunteers, as second generation seed from original hybrids, also yield less than the original hybrids. F2 seed (second generation) averaged 13 per cent less yield than F1, according to Agriculture and Agri-Food Canada research. Finally, we know that herbicide-resistant weeds have evolved, and it usually happens in fields where the same herbicide groups are used year after year.