Clear on Clearﬁeld More Clearfield herbicide-tolerant oilseed rape varieties will have been planted this autumn than ever before. Dominic Kilburn finds out why. AICC agronomist in Northumberland, Jim Callighan (right), says that it’s an easy decision for some of his growers to select herbicide-tolerant Clearfield varieties as part of their overall oilseed rape variety choice. Without them, oilseed rape is a non-starter to grow on parts of their farms. Jim started advising farmers to grow Clearfield varieties five years ago when they first became available on the UK market. “We target their use on problem fields where charlock literally chokes out the crop and makes the growing of oilseed rape impossible,” says Jim, who adds that the use of Clearfield varieties to control fumitory is also useful. “On one of my farms here in the North, as much as one fifth of the OSR area is now down to Clearfield varieties due to problems with
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weeds,” he points out. Initially he used varieties made available by breeders Pioneer and Dekalb, and now most of the major plant breeding companies offer Clearfield varieties as part of their portfolios. However, Jim believes that choosing a specific Clearfield variety is not the critical factor. “Typically these varieties will yield about 10 per cent less than the top yielding varieties on the Recommended List, but it’s the fact that it enables growers to bring land back into use with the crop that is the major benefit.” Clearfield herbicide comes in two post-emergence options; Clearanda (imazamox + metazachlor) and, more latterly, Cleravo, which is a metazachlor-free herbicide containing imazamox and quinmerac. Timing of application, says Jim, is when there has been a good
flush with weeds at the 2-6-leaves stage. Going later is an option but it’s always best to target the bigger, earlier flushes, he adds. “For me, Cleravo is the best choice as it broadens the spectrum of broad-leaved weeds controlled with the inclusion of quinmerac. I then go with propyzamide for the grass weeds later in the season, tank mixed with a fungicide. “Whereas when applying Cleranda there was less broadleaved weed control and the metazachlor post-em was ineffective against grass weeds, and so I still had to top up with propyzamide anyway,” he explains. “Clearfield does an excellent job on large charlock plants, fumitory, poppy, volunteer cereals and other weeds where there are very few other herbicide options available. “Also, if you grow HEAR OSR, it wipes out conventional rape volunteers preventing contamination,” adds Jim, who reminds growers that any Clearfield volunteers won’t be controlled by SU herbicides, although there are plenty of other autumn
DK Imperial CL is the most widely grown Clearfield variety in the UK with a combination of yield protecting traits.
residuals that will suffice. “Essentially, the agronomy for Clearfield varieties is the same as any other type; the same disease issues and harvest times etc., although they can be a bit leggy on fertile soils which is something to watch out for. “They have been a saviour for us in terms of growing oilseed rape and there are several newer varieties coming through from the breeders at the moment. “Ideally for the North would be a good Clearfield variety which also has club root resistance,” he concludes. ■