A winter oilseed rape production system originally only attractive to growers with serious cruciferous weed problems 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 the benchmark Kleffmann Group WOSR Amis® farmer input panel revealed at an industry briefing this spring.
Data from the 400-strong panel, carefully selected to be representative of British producers, show the 2017/18 Clearfield area more than doubling for the third year in a row. 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 Kleffman Amis 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 particular flexibility of 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 – which can be invaluable for accurate canopy management – they are highly effective against problem crucifers like runch, charlock, shepherd’s purse and hedge mustard,” said Mr Marris.
“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%.”
As a true post-emergence system, of course, Clearfield is highly flexible, ensuring the best herbicide activity regardless of seedbed quality or establishment method at any time from one to four true leaves of weeds and volunteers. However, it is important to note that Clearfield herbicides can only be used on CL varieties, warned Mr Marris. “Conventional varieties have no tolerance and will be wiped out.”
Alongside the system’s much wider grower value, impressive improvements in the all-round performance of Clearfield varieties also underpin its increasing 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 its 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 our vigorous establishment, rapid autumn development and pod shatter resistance traits. This all-round strength has enabled it and current stablemates, DK Impression CL and DK Impressario CL to deliver levels of 2017 farm performance every bit as high as today’s leading double lows.”