High erucic acid levels in winter oilseed rape are increasing at crushers and this could become even more acute as the acceptable level moves from 5% in oil to 2% in the near future.

But, one certain way of avoiding this is to grow a Clearfield variety of rape, according to Grainseed’s Neil Groom. This would not only control difficult weeds such as charlock, hedge mustard and runch, all of which have high levels of this substance within them, but also kills out any rape volunteers in the field.

He said Clearfield’s unique system meant that hybrid seed varieties and the use of BASF herbicides – Cleranda (imazamox + metazachlor) or Cleravo (imazamox + quinmerac) – were compatible. Using conventional breeding techniques, varieties have been bred to tolerate Clearfield herbicides.

By applying these herbicides post-emergence, all weeds and volunteer rape can be controlled, whilst the Clearfield variety is left to flourish. “This means growers can use Clearfield as a management tool, bringing fields back into rotation and controlling weeds and volunteer rape which may contribute to high erucic acid levels. A recent survey of Clearfield growers indicates that reducing erucic acid levels was the main reason they chose to grow these varieties,” he said.

The proposed reduction in the allowable erucic acid level of grain to 2% was increasing interest in Clearfield varieties, whereby the control of volunteers and brassica weeds was achieved.

And, there should be no yield penalty, said Mr Groom. “In NIAB TAG trials, Es Decibel CL was the top yielding Clearfield variety out of 16 tested, averaging a yield of 106% (4.41 t/ha) across seven trial sites harvested in 2017 and 2018.

“It is important, though, to get the timing and application of the post-emergent herbicide right when growing a Clearfield variety. Use at least 100 l/ha, but preferably 200l/ha, of water for good coverage and always add 1 litre/ha of the non-ionic surfactant Dash to improve leaf cover and uptake of the herbicide.

“Normally, the best time to apply the herbicide is when weeds have one to four true leaves and are actively growing (typically Sept to October). It is important to make sure that early weeds don’t get too big whilst waiting for the others.”

The only disappointing results he had seen was when the Clerando or Cleravo herbicide was applied late to weeds which were too large, or when the adjuvant Dash had been forgotten.