Building OSR Resilience
To cope with today’s uncertain commodity prices, restricted and less effective chemistry, growing legislative constraints and greater climatic variability, we look at five key areas for building greater resilience into oilseed rape production in this special mini-series.
Keeping it Clean
With the sheer scale of losses light leaf spot and phoma stem canker can cause, the most effective foliar disease management is a key priority in OSR resilience-building. In particular, specialists believe the emphasis must increasingly be on prevention rather than cure to minimise both sub-clinical losses and treatment costs.
“Maintaining a clean oilseed rape canopy throughout the season will do much to reduce unnecessary performance variations,” stressed Dekalb technical specialist, Will Vaughan-France. “Fundamental to this are high levels of disease resistance to protect crops from infections in the first place, limit their spread thereafter and achieve both at the least cost and risk whilst minimising the number of fungicide applications required.
“Although most breeders have also been appreciating the importance of foliar disease resistance 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 – just when spray days are at their most limited.
“Because Dekalb breeding has long prioritised the traits, all our mainstream double low varieties – DK Extrovert, DK Exalte, DK Exclaim and DK Exentiel – have LLS ratings of 6 or more and phoma/stem canker ratings of 8 or more,” he pointed out.
“As a result, they give the greatest possible leeway and flexibility in spraying while markedly reducing cropping risk. We also find this degree of disease resistance typically means only two rather and three foliar sprays are needed in a moderate disease season. And where disease pressures are higher a less expensive three spray fungicide programme can be employed. On average, this offers cost savings of around £24/ha – or £6/t for a 4t/ha crop.”
Openfield Agriculture’s Lee Bennett stresses that with a such a good range of high output winter OSR varieties with solid agronomics available these days there’s no excuse for anyone to grow crops with serious genetic weaknesses that increase both cropping risks and costs.
He identifies light leaf spot as a particular priority because it’s making its presence felt far more widely across the country these days and, just like Septoria tritici in wheat, current chemistry doesn’t appear to be as effective as it used to be.
“We need to stay firmly ahead of light leaf spot development if we are to prevent serious losses from the disease, and do so without incurring excessive costs,” insisted Mr Bennett. “Genetics is so crucial here that I believe extra caution is essential for varieties with light leaf spot resistance ratings of less than a true 6.0.
“With our eyes firmly on light leaf spot too, we need to be growing varieties with the best phoma resistance. As many growers have found in recent years, this enables them to focus their autumn fungicide programme on only a single late spray in November targeted at both diseases. That way they can hold back any phoma while nipping LLS firmly in the bud at the time when the first infections are occurring but well before they become apparent.
“This is why the robust combination of phoma stem canker and light leaf spot resistance available in varieties like DK Extrovert is so essential today. It almost certainly goes a long way towards explaining why this variety has remained such a firm favourite in the field across the country for so long despite never having been on the Recommended List.”
Alongside high vigour, disease resistance is a key priority for Jim Beeden in the 400 ha of winter OSR Flagleaf Farming grows to the north of Lincoln.
“Light leaf spot is particular concern these days,” he noted. “With a world of difference between 6 and 5 resistance ratings, we won’t touch a variety rated at less than 6. And we also want phoma scores of 8 or more. This prevents the disease getting in the way of early crop development and allows us to use a single November treatment to target light leaf spot as much as phoma for the greatest cost-effectiveness.”
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