Key to maximising oilseed rape output is the longevity of the crop’s green area index, but following last year’s difficult season there might be temptation to take a minimalist approach. CPM explores why it’s always worth investing in this crop.
“Paying attention to detail will ensure more consistent yields over time.” NIGEL SCOTT
By Melanie Jenkins
A far more favourable growing season means that those who’ve planted oilseed rape are likely seeing much healthier crops than last year. However, managing both green area index and green leaf area can help growers to capitalise on this improvement further.
Looking back at autumn 2023, it was a devastating establishment period for OSR, especially in the North of England, where ProCam’s Nigel Scott recalls half the planted area being lost. “I rarely write crops off but the pressure from cabbage stem flea beetle that autumn was biblical. Those crops that survived weren’t great, and then the dull conditions in June and July meant seeds were small and yields were low.”
PLANTING DECLINE
The kick-back from this was that some growers decided to not take the risk in 2024/2025, with estimating plantings in Nigel’s area down by 10%, he says. “However, others recognise OSR as a useful and profitable option. If you can grow it and achieve a good margin, it’s a true break crop and helps control grassweeds.
“Those who committed may have drilled a little early, opening the door for clubroot, but many crops haven’t required insecticides and so have thrived. The situation now is the opposite to what we experienced last spring.”
Last year, many crops were patchy with a low green area index, but as of early February, Nigel has observed GAI of 3 in places. “You couldn’t have two more different years sequentially.”
Because of this contrast, he fears some might take a ‘low input, low risk’ approach to their OSR crops. However, he stresses that OSR must be managed carefully to maximise its potential. “With prices on the rise – north of £400/t – you want to maximise your crops, not just settle for the bare minimum.
“I understand many may have lost out financially last year and don’t want to spend this season, but we can’t farm according to last year’s conditions. We must treat this year as fresh, focusing on agronomy on a field-by-field basis.”
Yara’s Natalie Wood agrees that this season has provided more favourable conditions but notes there’ll be more variability out there after the winter. “Variability can occur within fields, which can create challenges when deciding how to approach a crop.”
First and foremost, Nigel advises growers to assess their weed burden and herbicide applications. “The majority of crops in the North have had a broadleaf and grassweed herbicide, and what I’ve seen looks clean.
“Be aware that clopyralid, the active in Korvetto (clopyralid+ halauxifen- methyl) and Shield Pro (clopyralid), shouldn’t have been applied until 1 March. You also won’t have been able to apply Kerb (propyzamide) and Astrokerb (aminopyralid+ propyzamide) since the end of January, so you’ve been in a ‘no man’s land’ for herbicides during that period. But be cautious when you do go into a crop, ensuring it’s before green buds emerge.”
He then suggests assessing crop biomass with tools such as FieldSense. “If GAI is 1 or less in early spring, apply nitrogen, but if it’s above 3, it might not be necessary. It’s all about measuring and managing appropriately.”
CROP UNIFORMITY
Alternatively, growers can use Atfarm, Yara’s digital software, to create variable rate maps to even out growth, says Natalie. “We’re aiming to maintain GAI between 3 and 4, and the first nitrogen application will help to achieve a more uniform crop.
“Using the Atfarm app also helps track nitrogen uptake which allows adjustments based on overwinter mineralisation,” she adds. “Ammonium nitrate is immediately available to the plant while urea must go through several stages before it becomes available to plants. In cases where crops are behind, the sooner nitrogen becomes available, the better.”
It’s also crucial to assess disease which will be influenced by the weather, suggests Nigel. “I’ve seen some light leaf spot so far but it’s important to anticipate potential challenges rather than react once disease has spread.”
When considering plant growth regulators (PGRs), he emphasises that OSR can be easily manipulated. “For forward crops, PGRs can keep the growing point down, minimising height and encouraging root mass development.
“If the crop is already large, any product with metconazole will regulate growth, best applied early in the season. For later regulation, at green bud stage, use a PGR fungicide like metconazole or Toprex (difenoconazole+ paclobutrazol). This will open the canopy and promote lateral branching, which is ideal because we want a dense canopy to maximise pods and seeds.”
Nigel suggests tissue testing regularly to maintain nutrition, as OSR requires more frequent testing than cereals. “OSR requires boron and molybdenum, so test for these and address any other deficiencies promptly.”
Sulphur is also vital and should be applied early and in small, frequent doses, he says. “Be mindful of leaching risks to avoid losing the benefits of the application while remaining environmentally conscious. Peak sulphur uptake occurs later in the OSR season, but is required for efficient nitrogen use. If applied early, don’t overdo it, as excessive sulphur can hinder boron and molybdenum uptake.”
Natalie advises using a fertiliser that provides both nitrate and sulphate. “OSR is hungry for sulphur which improves overall nutrient use efficiency.” She adds that at the end of flowering, applying foliar nitrogen can help to extend the green area duration, she says. “The plant’s pods can photosynthesise, so extending the green period with foliar nitrogen, such as Nufol, can increase yields by up to 0.3t/ha.”
BOOSTING ROOTING
In cases of poorer crops, Nigel recommends phosphite to encourage rooting. “Later in the season, consider biostimulants like pidolic acid during flowering when nitrogen can be an issue. This can help to maintain green leaf area which supports seed pod filling and improves nitrogen efficiency. A late-season foliar nitrogen application, just as petals fall off, can raise oil content and yields.”
Finally, Nigel addresses insect concerns, noting that pollen beetle isn’t a significant problem in the North. “I’m reluctant to use insecticides on OSR because they often don’t provide comprehensive control due to resistance, and they could make the situation worse due to their effects on beneficial insects.”
When it comes to OSR management, consistency is key, he reminds. “Rotation plays a large role, with wider rotations leading to larger yields. Equally, paying attention to detail will ensure more consistent output over time,” concludes Nigel.
This article was taken from the latest issue of CPM.
For more articles like this, subscribe here.
Sign up for Crop Production Magazine’s FREE e-newsletter here.
