When it comes to selecting oilseed rape varieties there is something of a North/South divide, so attention should be paid to regional and local performance when making decisions.
The AHDB Recommended List undoubtedly serves as a useful general indicator of how oilseed rape varieties are likely to perform, but local experience is also invaluable in order to fully assess the performance and reliability of specific varieties under individual farm conditions, Kat Allen, oilseed rape seeds manager for Syngenta, advises.
Her recommendations for the iOSR group are to visit local trials sites and assess crops on neighbouring farms to identify which varieties had the potential to perform consistently well under their own conditions. She also advised them to examine the physical attributes of different varieties to better match growth habits to individual farm situations and weather conditions.
A field exposed to the full force of freezing easterly winds in winter, for example, could require a variety with a completely different growth habit to one produced on a sheltered site. What is practical on a farm scale is always a compromise, but growers can tip the scales in their favour by looking for varieties which are most appropriate to their specific situations.
Experience on Syngenta Innovation Centre trial sites this season highlighted whereas the company’s new variety, SY Florida, put on exceptional early autumn vigour, SY Harnas was far more compact over the winter. However, SY Harnas grown on northern and Scottish sites was unaffected by a cold snap and subsequently powered away in spring, putting on new growth and setting up well to take advantage of longer day length over summer.
Ms Allen explained: “That experience has clearly demonstrated how a variety with the growth characteristics of SY Harnas is very well suited to harsher winter conditions in the North and Scotland, while SY Florida will perform to its full potential in sunnier conditions of the South and East.”
The harsher winter conditions in Scotland have a significant impact on plant physiology, with an average 42 days of frost from January to March and an average minimum temperature of -0.2degC, compared to southern England’s 32 days of frost and an average minimum temperature of 1.3degC during the same period.
Furthermore, central Scotland has more daylight than southern England during July, 17 hours 25 minutes compared to an hour less in the South. However, the light intensity in Scotland is generally lower, with an average 140 hours sunshine in July, compared to 185 hours for England as a whole, and more than 200 hours in the southern region.
To take advantage of the climatic conditions, crop canopy can be influenced by the variety’s growth habit and its agronomic management. Seed rate and autumn establishment set the foundation for the crop’s architecture, which can still be effectively managed and tailored in spring with Toprex PGR and Amistar fungicide programmes.
“An oilseed rape crop’s yield potential is established with the canopy architecture created during the growing season. However, only in the final few weeks before harvest can that can be utilised to produce the high seed and oil content which will generate optimum returns for growers,” Ms Allen said.
“Plant height and maturity date are essential genetically- programmed elements of that, which growers can exploit through the establishment, nutrition and agronomy management programmes they use.
“What we have heard repeatedly from growers in the iOSR group is that consistency and reliability are the key attributes for variety selection.”
For the second consecutive year most growers have experienced crops which went through the incredibly mild autumn and early winter with very strong and vigorous growth, only to physically go backwards and reduce in crop canopy during a relatively cold snap in late-February. In almost all instances, it was the knee-high, forward crops which suffered the most severe hit.
Highlighting the implications of this, Syngenta seeds manager Mark Bullen added: “When green leaf area is decimated by frosts, the nitrogen which was used to generate that growth is effectively lost to the growing crop. It takes about 50kg of nitrogen to build one unit of green area index, so if N is used to produce excessive autumn growth of leaf which subsequently dies back and drops off that is effectively wasted in terms of the current crop.
“Although following crops will benefit to some extent from the residual return of this biomass, this ‘lost’ N will have to be replaced with expensive bagged N to rebuild the green area in the current crop.
“Crops which were more compact through winter are better placed to use the higher remaining levels of soil mineral N not taken up by the crop in autumn, with hybrid vigour driving the new growth in spring.
“This is one of the key reasons why SY Harnas has performed so consistently as the highest yielding variety for Scotland and the north of England. It provides a real example of how selecting a variety most appropriate to the climatic conditions and in-field situation can make a real difference in delivering reliably higher yields and gross output on your farm.”
Growers should be aware light leaf spot and phoma resistance ratings on the AHDB Recommended Lists are generated from limited trials results, and applied universally across the UK listings from the same trials, irrespective of variable disease pressures.
Mr Bullen said: “Resistance ratings offer an extremely useful tool to help with managing the crop and spreading risk: higher resistance ratings generally slow the onset and development of disease in the crop and can give greater flexibility in fungicide application timing. However, there is no substitute for monitoring crops in the field for phoma leaf spot thresholds and risk assessment of light leaf spot disease pressure to tailor preventative fungicide treatments.”
This message was underlined by ADAS plant pathologist Faye Ritchie, who said there was a significant difference between a variety which had a relatively low resistance rating of 4 compared with one with a 6, for example. However, there could be relatively little difference between a 6 or 7, and they would effectively be managed the same in the field.
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