Reducing Winter OSR Growing Risks 08-Jun-2017

Oilseed rape growers across the south east can reduce their establishment, management and  crop marketing risks substantially with a novel production system that has been catching on in a big way in the past year, suggests Andrew Bourne of Ashford-based seed specialists, T. Denne & Sons.

“Managing the up-front cost of winter rape growing as well as improving the crop’s chance of establishment success has become a priority for many,” he pointed out. “It’s so much more important these days to minimise your risks of crop failure from a dry autumn or flea beetle attack, in particular.

“Equally important is over-coming the volunteer OSR and cruciferous weed problems that can compromise spraying programmes, canopy management and desiccation timing. Planting 55 seeds/m2 of a variety with the traits you have chosen and actually growing 100 plants/m2 of a mixture of numerous very different and less desirable variants, with a massive range of disease resistances, stem characteristics, maturity dates and oil qualities certainly doesn’t make for effective or economic use of expensive crop inputs.

“And finally, the last thing you want when sending your crop to the crush is a hefty claim for high erucic acid levels.


“The volunteer threat from the amount of HEAR that has been grown regionally in the past plus the surprising levels of erucic acid we know can come from charlock, hedge mustard, runch and other cruciferous weed seed is a vital consideration here. Sampling and analysis of OSR samples at crusher intake is becoming more rigorous, so quality management at farm level is crucial”

Against this background, Andrew Bourne finds the dramatic increase in the popularity of Clearfield  (CL) varieties bred to be resistant to imazamox herbicides across the country over the past two seasons unsurprising.

Last year alone, the national Clearfield area more than doubled to 30,000 ha and is expected to do so again this autumn as existing growers build-on their success and more growers appreciate the system’s particular benefits.
“The Clearfield system gives you significant control of both cruciferous weeds and OSR volunteers, as well as a wide range of other broad-leaved weeds, grass weeds and cereal volunteers” he explained. “At the same time, it enables you to delay controlling them until your crop has safely developed to 2-4 true leaves. So you don’t have to make the investment until you’re sure you have a crop.  You also avoid the risk of any set back to establishment from pre-emergence herbicide applications as well as any SU residues from preceding cereals.

“Good levels of control of non-Clearfield volunteers means you grow what you sow too. That way you can match your fungicide and PGR programmes much more effectively to the varieties you’re actually growing, you have far fewer challenges in securing the most productive canopies and  your desiccation timing can be much more precise.

“Add in the value of controlling both the key external sources of erucic acid contamination and the system’s particular value in reducing OSR growing risks is crystal clear.”

For the first three years after its introduction in 2012, Clearfield OSR growing was largely confined to situations in which difficult-to-control weeds like charlock, runch and hedge mustard were making profitable rape growing almost impossible.  


However, Andrew Bourne has no doubt that the rapid progress in yield improvement and agronomics achieved by breeders and the greater appreciation of the system’s wider advantages by growers have been responsible for making it far more of a mainstream choice today.


The first independent Clearfield trials undertaken by NIAB-TAG on three sites last season, indeed, showed both DK Imperial CL and the other top performing variety of the nine tested delivering gross outputs of 3.8 t/ha in a generally low yielding season.

“It’s good to see yields comparing well with non-Clearfield varieties, these days,” he commented. “But it’s the first class agronomic characters the leading CL varieties now have alongside their output potential that are equally valuable for growers wanting to reduce their OSR risks.

“DK Imperial, for instance, carries some of the best available phoma/stem canker and light leaf spot resistance ratings at 8 and 6 respectively. Vigorous establishment ability coupled with a medium to rapid autumn growth habit make it able to cope with less-than-ideal sowing conditions and drilling delays. And its pod shatter resistance markedly reduces the risk of seed losses in the run-up to and at harvesting.


“I see pod shatter resistance, in particular, as crucial with Clearfield varieties,” stressed Andrew Bourne. “Growing only what you sow is a huge benefit of the system. But in volunteer terms, it’s a once-only reset. Clearfield volunteers in future Clearfield crops could be as much as of a problem as volunteers have always been to date.

“So you have to take the opportunity of the reset the system gives to work at reducing future volunteer problems. Pod shatter resistance can really help you cut down seed shedding here. Alongside it, the best post-harvest stubble management will also be vital. In particular, you should leave any shed seed on or near the surface to chit and spray it off with Roundup before drilling your next crop. Cultivate too early and all you will do is bury the seed to cause you problems in the future.”

The Clearfield System in Summary

  • A key part of a more flexible autumn herbicide strategy to manage risk and upfront costs
  • Suits drilling systems where pre-emergence herbicides can be problematic
  • Significant control of non-Clearfield OSR volunteers (including HEAR)
  • High impact on cruciferous weeds (which also contribute to erucic acid contamination)
  • Good contact control of cereal volunteers, bromes, wild oats and ryegrass
  • Valuable tolerance to residual levels of SU chemistry from previous cereal crops


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