With weed control in oilseed rape moving almost entirely from pre- to post-em in recent years, how can growers ensure they keep damaging broad-leaf problems firmly in check?
It wasn’t so long ago that pre-em metazachlor, dimethenamid-p, quinmerac or clomazone were pretty much standard for keeping on top of chickweed, mayweed, speedwell, cranesbill, poppies, cleavers and other broad-leaved weed threats in OSR.
All this has changed with the largely CSFB-driven imperative to delay as much investment as possible in the crop until it is safely established. The extent to which pre-em herbicides can both add to crop establishment stresses and cut down on options for replacing any that fail have also been significant considerations for many. As has the fact that the best conditions for pre-em activity aren’t necessarily achieved by many of today’s single pass establishment regimes.
“The increasing use of companion crops is another obvious factor here, ” adds Bayer commercial technical manager, Darren Adkins. “Encouragingly, though, at least as important in the move away from pre-ems has been the increasingly good post-em herbicide alternatives now available.
“The Clearfield system has, for instance, give those with charlock, runch or hedge mustard problems a much better option than hoping for enough winter frost to enable bifenox to do the job. Varieties bred to be resistant to imazamox enable this highly effective active on brassicas to be used in combination with either metazachlor or quinmerac.
“Equally, the arrival of Arylex (halauxifen-methyl) combined with picloram in the autumn or clopyralid in the spring has been really useful for those needing to keep on top of cleavers, cranesbill, mayweed, fumitory and poppies, in particular. While the spring option is more limited in its window of use, the autumn one can be applied from two true leaves until the end of December, making it very flexible.”
Both the autumn Clearfield and Arylex alternatives are best employed at up to the four-leaf stage of the weeds for the most reliable results, Mr Adkins advises. And they need to be integrated carefully with grassweed controls – especially with the minimum 14-day restriction on any application before and after clethodim use.
“There may still be a place for pre-ems on lighter ground where establishment is seldom a problem and reliably good conditions can be achieved for their activity,” he says.
“But, I would always opt for a Clearfield approach wherever cruciferous weeds are problematic. Where other broadleaves are the main target then autumn Arylex is clearly the best post-em bet.
“Of course, an early graminicide always has to be part of the strategy as volunteer cereals are so competitive, with propyzamide equally important once soil temperatures cool sufficiently to ensure the most effective grassweed control in the rotation.”
