IT MIGHT have been controversial at one time, but now the 'Clearfield' winter oilseed rape production system has become king of the crop in the UK.

Originally attractive to growers with serious weed problems, it has mushroomed in popularity over the past four years to become the single biggest individual sector of the British crop.

From less than 1% of national plantings in 2014/15, Clearfield OSR has expanded to make-up more than 10% of this season’s 600,000 ha national crop, according to the latest results from a benchmarking farmer input panel.

Data from the 400-strong panel, which was selected to be representative of British producers, showed the 2017/18 Clearfield area more than doubling for the third year in succession. Indeed, it is now larger than national areas of high oleic low linolenic (HOLL) and high erucic acid rape (HEAR) combined.

“Clearfield OSR has become firmly mainstream,” said Mark Shaw, of leading breeder, Dekalb. “The data also show a third more farms using the system this season than last, with double the number growing Clearfield varieties alone. What’s more, the stand-out market leader, DK Imperial CL, is now the sixth most widely grown of all winter rape varieties.

“The escalating popularity of the system must be due to benefits that go well beyond the genetic resistance of Clearfield varieties to imazamox, allowing post-em applications of the herbicide to be used to deal with difficult-to-control cruciferous weeds.”

Clearfield originators, BASF, see the system’s main attraction to growers and agronomists coming from three key areas – the crop’s rapid start, the widest weed control and its flexibility to herbicide use.

“Being tolerant of SU herbicides, Clearfield varieties are well able to cope with any residues that might be present following a winter wheat crop,” pointed out the company’s field crops manager, Dave Marris.

“This and their hybrid vigour gives them a valuable edge in getting the rapid and reliable start vital with winter OSR in the face of multiple establishment challenges.

The Clearfield herbicides, Cleranda (imazamox + metazachlor) and Cleravo (imazamox + quinmerac) also remove the widest range of weeds of any single product on the market.

As well as controlling most major broadleaves and both cereal and OSR volunteers, they are highly effective against problem weeds like runch, charlock, shepherd’s purse and hedge mustard. “Together with any HEAR volunteers, these are known sources of erucic acid, making the system good news for growers concerned over penalties or rejections where rapeseed levels exceed 2%,” pointed out Mr Marris.

Improvements in the all-round performance of Clearfield varieties has also helped boost their popularity. “The first variety with the trait to join the Recommended List in 2013/14, DK Imagine CL, was a good 5-10% off the pace in gross output,” pointed out Dekalb technical specialist, Will Vaughan-France. “It was also a shatter-susceptible semi-dwarf with average disease resistance ratings and less rapid autumn development than our mainstream hybrids.

“Since then, yields, oil contents, traits and agronomics have all come on by leaps and bounds. So much so that today’s DK Imperial CL has a two year average gross output midway between farmer-favourites, DK Extrovert and DK Exalte in our national trials.

“It shares strong phoma and light leaf spot resistance ratings with these mainstream varieties, together with vigorous establishment, rapid autumn development and pod shatter resistance traits," he added.