WHILE DISEASE control in oilseed rape crops is important, it’s not just chemical control that can be used – other elements can also help.
At Duncan Farms, in Aberdeenshire, getting oilseed rape up and away quickly is the key. With heavy rainfall and plunging temperatures often sweeping in around October and November, bringing with them the threat of slugs and light leaf spot (LLS), careful planning and a clear strategy are required to ensure success.
“I like to get all the OSR in the ground in August, as I don’t really like sowing the crop in September,” said Sandy Norrie, the arable manager at the farm. “It’s usually possible to do that – this year we started on August 12 and the last field went in by August 24, so we got it all done in 12 days.
“You want to get it up before the heavy rain comes in, so when it does and the slugs appear, it doesn’t matter because the crop is huge. So, if we can get it up and away before the slug stage and make it hardy enough for winter, that’s ideal.”
David Waite, seed manager at Frontier, agreed that it was crucial to get going early due to the short window between the winter barley harvest and the onset of colder weather: “I’ve seen the temperature in October drop quickly to mid-to-low single figures and OSR doesn’t really grow in those temperatures. You need to get the crop established before then.”
With 6000 acres of combinable crops, oilseed rape forms part of a five-year rotation that includes winter wheat and three years of winter barley. So, early establishment for Duncan Farms is crucial for the crop, and Mr Norrie selected his varieties with one eye on the agronomic characteristics that would maximise the benefits of having sown so early.
For this reason, he grows 80% hybrid and 20% conventional OSR, the balance born from a focus on a variety’s agronomic characteristics, rather than seed cost.
“Early establishment and vigour are so important for us,” he noted. “Hybrids are always good towards the end of August – they can get going quickly, plus we can drill at 40 seeds per square metre, which makes for a good, even cover in the spring. You don’t want something that looks like a mass of cress!
“I choose the varieties that I think will work best. The upfront cost is not the main priority for me – the most important consideration is the variety and the characteristics it has. 
“When I take into account the difference in seed rate between hybrids and conventionals, that difference is only £8 over the acre. I don’t mind paying more for that extra hybrid vigour to get the crop going.”
Each OSR variety brings with it different advantages and previously he planted a mixture of varieties such as Mendel, Cracker and Barbados. This year, he was again careful to ensure that each variety was chosen for specific characteristics, speaking to agronomists, looking at trials, and attending Cereals in June in order to select the most suitable varieties.
“Mentor is one of the mainstays now. We’re a little restricted because clubroot is a key concern for us – 60%of our ground has clubroot. We have to go with clubroot resistant varieties, which have gradually improved but still have a more limited yield potential.”
He continued: “Barbados did well for us previously, but it was a bit on the late side, so we went with its stablemate, Flamingo. We also had a strip trial of InVigor 1020, which did well. We had a yield map of the field, and you could pick out the strip from the rest of the crops in the field – in a positive way!”
Another new one, InVigor 1030, had the vigour needed to gain the most benefit from the early sowing and grow away from the threat of slugs, said Mr Norrie. He is now growing 34ha of it, having been impressed by it at Cereals. 
As well as its vigour, he also saw major positives in the variety’s high oil content (47.1%) and light leaf spot rating (6).
“Light leaf spot (LLS) is a far bigger problem for us up here than phoma,” he pointed out. “We don’t need a high phoma resistance, although at a 9 it is the best available, and cabbage stem flea beetle is thankfully not such an issue either – the climate helps with that. 
“But LLS is a major issue in Scotland. Most of the Mentor would need two LLS treatments, whereas with the resistance built in to newer varieties, we get away with just one.”
LLS is a particularly damaging disease across swathes of the UK, with Rothamsted Research’s preliminary forecast suggesting that two-thirds of crops were likely to suffer more than 25% infection of it in the 2016-17 season. 
In light of the reduced chemical armory that growers have to combat LLS, Mr Waite said varietal resistance to the disease is more significant than ever: “LLS is getting more difficult to control, so inherent genetic resistance in varieties is going to become more and more important as time progresses. 
“When I select varieties, I first and foremost look at which ones have the best LLS resistance alongside their gross output,” he added.
At Duncan Farms, last year’s OSR harvest came to 4.1 tonnes per ha, down from the record 4.7 tonnes per ha achieved the previous year but only slightly below the five-year average of 4.4 tonnes per ha. Mr Norrie is optimistic about this year: “Last time around we didn’t really have the best May, June or half of July in terms of the conditions. But this time things got off to a tremendous start and all our OSR looked very well going into winter.”