Protecting oilseed rape crop’s green leaf area could prove crucial this season to enable crops to compensate for the late spring and give them the chance to fill pods and seed.
After the promising establishment and strong growth for most of the iOSR growers’ crops, they reported plants went backwards in the cold March winds, with fertiliser applications to recover growth further delayed by wet soil conditions.
Strong rooting over autumn had given the foundation for good crop performance, according to Syngenta technical manager James Southgate.
“But if they are to reach their potential it will be all about building and maintaining the green leaf area post-flowering.“
"Studies have shown that, unlike cereals where plants can move stored energy around and up to the grain heads, in oilseed rape all yield and seed oil content is set by light capture and utilisation after flowering,” he advised.
Analysis of the Yield Enhancement Network (YEN) results in 2017 highlighted the top performing crops for both yield and efficiency had 10 days extra time from the end of flowering through to desiccation – enabling plants to fill seeds more effectively. These seeds were typically bolder and with a higher oil content to increase gross output per hectare.
One of the key targets for growers is to consolidate flowering, into a shorter but more intense period.
Mr Southgate advocated it can be hugely beneficial to start flowering a few days later, when the risk of frost is reduced, and then finish earlier to open up the green leaf area to more light.
“The flowers themselves reflect light away from the crop, so actually reduce a plant’s photosynthetic activity. The shorter the duration of flowering, the more light the crop can absorb.”
Short, intense flowering is no limit on achieving the YEN target 100,000 plus seeds per square metre, with the competition winner, Wiltshire-grower Martin Smart, a long-term advocate of PGR use to manage crop canopy and manipulate flowering.
After the late cold easterly winds and snow to the middle of March this season, crops were primed to go into rapid stem extension, with the main raceme shooting ahead and side branches being slow to catch up – with the prospect of a protracted flowering period which could seriously limit plant potential.
PGR treatments in mid-to-late March, at the stem extension timing, gave the chance to hold back the main raceme and even up crop growth, to enhance plant structure and synchronise flowering into a shorter period, advised James Southgate.
“A further advantage of the shorter flowering is that it reduces the sclerotinia infection risk period, when falling petals provide the food source for disease spores which can enable them to penetrate into the plants,” advised Mr Southgate.
“Reduced duration of petal fall means your Amistar treatment can achieve the best possible results for disease control, and give the crop a real physiological boost in green leaf retention and photosynthetic performance.”
He pointed out that even in a season with low sclerotinia disease pressure – which in reality is more often than not – the strobilurin green leaf retention of Amistar still gave an economic return.
The YEN project results had also pinpointed the highest yielding crops had all received an extra fungicide pass.
“Where we are looking to delay senescence and extend the green leaf performance of the crop it’s still important to control the later infection of leaf diseases, including alternaria and leaf spots, where Amistar is also effective,” he added.
Berkshire iOSR grower Joe Dilibero reported the first nitrogen did not get onto the crop until the second week of March, when he managed to get 100kg/ha on after the snow and strong winds abated. However, crops were still looking exceptionally well and pleasingly clean – of both disease and black-grass.
In the East, Chris Eglington was also relatively late, with the first N looking to apply 125kg/ha of ammonium sulphate by mid-March – with winter barley and second wheats taking a priority.
“I don’t think there’ll be any problem getting to a GAI of 3.5 at flowering,” he said. “So we are not in any hurry.”
Image: iOSR Grower Martin Smart
In a further initiative to extend the green leaf performance of oilseed rape and energy capture this season, Mr Southgate urged growers to look at their desiccation practices – which will also be assessed on the Syngenta iOSR Focus Sites in Suffolk and Lincolnshire this summer.
While the natural inclination is to get the crop cut and safely in the barn as soon as possible, early desiccation may be curtailing the crops’ potential. That may particularly be the case with slower-acting glyphosate desiccation, which could start to have an impact on plant physiological activity long before it takes effect to make it ready for harvest.
Some iOSR growers are already trialling leaving crops to senesce naturally, but acknowledge the risk of weather disasters – albeit somewhat mitigated by the use of pod adhesives – along with the implications for slower combining of greener stemmed material.
“With later crops this season, there could be a compelling argument to manage desiccation with Reglone,” he said. “The crop can get a week to 10 days extra green leaf activity before spraying and rapid kill, which could give a useful boost in seed fill and oil content, and still manage to get a reliable clean harvest date.”
Whatever desiccation route is chosen, all iOSR growers can take a tip from Mr Smart when it comes to combining; he always advocates cutting as high as possible to take just the seed bearing branches and reduce the material going through the combine. It significantly improves the speed of cutting, and the quality of the result, he reported, and gets the crop gathered in faster – longer green stems left in the field can be dealt with when they have died off and easily shatter, he added.