Dekalb Technical Specialist
To reduce the risks of winter oilseed rape production and increase the flexibility with which the crop can be managed we need far greater reliability in the varieties we grow.
At around £350/t before oil bonuses, rapeseed prices today are almost £100/t up on this time last year. This and firm market prospects for the foreseeable future make the crop an attractive proposition. But only if we can achieve a consistency of performance that we often struggle to realise in practice.
Winter OSR faces more than its fair share of growing challenges. It frequently needs to be sown later than many consider ideal and into less-than-ideal seedbeds. Flea beetles, slugs and pigeons – not to mention extremes of both dry and wet weather – all threaten establishment and early development. Winter and early spring conditions can easily affect plant development and get in the way of key spray and fertiliser timings. Both prolonged flowering and difficulties in applying late bagged nitrogen can restrict pod fill. And stormy weather or delayed harvesting can cause serious shedding losses.
Gross output measured under the best possible small plot trial-growing conditions gives a good idea of the potential of modern varieties to perform. High output potential alone, however, simply isn’t enough to deliver reliably above-average yields and oil contents under such commercial farming challenges.
Instead, to reduce the risk and increase the flexibility of winter OSR production for the most consistent performance we need varieties with a robust agronomic package as well as a high output potential.
Essentials in this respect in my experience are vigorous establishment and the greatest ability to recover from climatic, pest and disease setbacks; the best possible resistance to both phoma stem canker and light leaf spot – and increasingly also perhaps, clubroot; and the right degree of resistance to pod shattering.
In addition to showing their strengths in our breeding work – all of which is untreated to maximise the pressures on them – varieties with these vital traits are also proving much more popular and longer-lasting with UK growers.
Vigorous establishment to four true leaves is a trait we’ve always prioritised both in varieties that suit earlier drilling and in those better able to deal with sowing well into September by virtue of their particularly fast leaf development. It primarily relates to their ability to put roots down and access nutrients rapidly and robustly.
Long periods of autumn drought or sustained early season flea beetle or slug pressures will always create problems for OSR establishment. But where conditions are less extreme we know that varieties with the trait are better able to deal with difficult seedbeds, lack of moisture and early slug and insect attack. This can markedly reduce the risk of crop failure.
Foliar Disease Resistance
Also important in getting crops through those first few critical months as cost-effectively as possible is a high level of phoma/stem canker resistance. Combined with vigorous establishment, it enables crops to grow through disease pressures that would defeat less robust varieties without early fungicide support.
Double phoma resistance – the RLM7 gene supported by high levels of poly-genic resistance – has proved invaluable in parts of Europe experiencing particularly severe phoma pressures in recent years.
It also delivers the goods where phoma is less of a problem, significantly reducing the likelihood of reaching the spraying threshold early in the season, if at all.
As well as making autumn fungicide treatment less time critical, reliable phoma/stem canker resistance enables it to be focused on a single late spray in November targeted at least as much on light leaf spot. So this increasing disease threat can be firmly nipped in the bud when the first infections are occurring but well before they become apparent.
We typically find the resistance ratings of 8 or more for phoma/stem canker and 6 or more for light leaf spot carried by all our mainstream varieties mean two rather than three foliar sprays are needed in a moderate disease season.
Although the importance of high levels of resistance to both diseases has been more widely appreciated in recent years, only 25% of the 28 varieties on the current Recommended Lists have light leaf spot resistance ratings of 6 or more and phoma/stem canker ratings of 8 or more. And worryingly, two of the four varieties gaining Recommendation this year have ratings of just 4 for phoma/stem canker resistance.
This means far too many crops are still reliant on the earliest disease identification and most timely fungicide treatment from late autumn to early spring.
Pod Shatter Resistance
Another trait being increasingly recognised for its commercial value in OSR risk reduction is pod shatter resistance.
Independently estimated to average 15-20% per year, oilseed rape shedding losses are known to exceed 70% after adverse weather or where harvesting is unduly delayed. Quite apart from the loss of revenue, this has major implications for volunteer control in subsequent crops.
John Innes Centre testing with a well-proven Random Impact Testing protocol has confirmed marked resistance to pod shattering in our varieties.
At the same time, NIAB-TAG delayed harvesting trials at two sites with eight modern varieties under notably low shatter conditions have underlined the value of the trait in practice.
On average, the four Dekalb pod shatter resistant varieties in the trials yielded almost identically to the non-resistant controls when harvested on 23-24 July. When harvesting was delayed for seven days, though, the non-resistant varieties yielded 6% less than the resistant ones, the gap widening to 9% after a further seven-day harvest delay.
Even assuming a conservative 4 t/ha initial yield, the sort of delay that would be quite normal on many farms with workloads as pressurised and weather conditions as variable as they are today represents a yield saving of just under a quarter of a tonne per hectare from pod shatter resistance. This is worth around £20/t at current crop values.
It just goes to show how valuable shatter resistance can be in allowing harvesting to be delayed without risk to take full advantage of the longest possible pod-fill. This is important as we know many growers are desiccating their OSR a good week too early in the interests of security, and every day of pod filling lost reduces oilseed rape yields by 1-2%. We also know that seeds accumulate most of their oil in the second half of seed filling, so the gross output losses from harvesting too early for fear of shattering are even greater.
Other Reliability-building Opportunities
Countering the noticeably wider incidence of clubroot being encountered across the UK is also becoming more important these days. Indeed, a national agronomists’ study this spring revealed almost two thirds (63%) experiencing more problems with the disease in recent years – nearly 70% of these in fields where they’d never previously seen it.
The new generation of clubroot resistant varieties coming forward with more competitive performance levels and all the benefits of vigorous establishment, double phoma resistance and pod shatter resistance are providing a timely solution to this threat.
Clearfield varieties bred to be resistant to imazamox herbicides provide another opportunity for OSR growers to reduce risk and improve flexibility.
First and foremost, they enable the problem cruciferous weeds like charlock, runch and hedge mustard which can serious compromise profitable rape growing to be effective controlled. This and their ability to control volunteer rape from seed surviving in the soil for many years, also makes them valuable in reducing the risk of erucic acid contamination.
By moving broad-leaved weed control from pre- to post-emergence too, the Clearfield system means crops can be treated only once they have safely developed to 2-4 true leaves, reducing any risk of setting-back OSR establishment. In addition, imazamox resistance protects the crop against SU residues from previous cereal crops that may also affect establishment.
With these advantages, it’s not surprising the latest industry figures show the area planted to Clearfield varieties has more than doubled in the past year to some 30,000 ha. Nor that it is set to do so again in the coming year with the increasing availability of varieties carrying more of the core resilience-building traits.
Finally, we mustn’t forget the low biomass trait which is also now becoming available in progressively higher performing varieties with class-leading agronomics.
Enabling winter OSR to be drilled with the greatest sowing date and rate flexibility even on high fertility sites and fertilised late in the spring without any danger of lodging, this innovative character will be providing far more growers with far greater resilience – not to mention ease of management – in their crops in the years ahead.
Like semi-dwarf wheat, building the low biomass trait into the right high performance background has taken time. However, for the future it promises to be every bit as important a breeding development as it has already proved to be in wheat-growing. It’s certainly something to keep a very close eye on in the years ahead.
Click here to view our varieties that contain Pod Shatter resistance, phoma/stem canker resistance Vigorous establishment, and our Clearfield varieties