Without any prolonged period of cold weather, this season will reward particularly careful oilseed rape canopy management growers
Without any prolonged period of cold weather, this season will reward particularly careful oilseed rape canopy management growers were advised at the first of this year’s joint Dekalb, BASF and Yara 3×3 Initiative technical events in Lincolnshire.
Left to right: Ruth Stanley, Ian Matts and Will Vaughan-France pictured at the 3×3 technical event in Lincolnshire.
Speaking at the mid-February event held at the Initiative’s northern trial and demonstration site hosted by Flagleaf Farming at Burton just to the north of Lincoln, Dekalb technical specialist, Will Vaughan-France explained that the exceptionally mild winter has left most winter rape crops approximately a month ahead of normal in their development.
Not only that but across much of the country different varieties growing alongside each other are at very different growth stages, despite carrying similar amounts of green area in many cases; the faster spring developers already moving into stem extension and beginning to show flower buds while the slower developers still have their growing points at or around ground level.
“Thankfully, most crops are well-rooted,” he pointed out. “But the earliness of the spring and the extent of the differences in development between varieties will make particular care in fertiliser and PGR applications essential for the most productive canopies. “This will be complicated by the relatively high levels of disease obvious on many crops.
Significant amounts of active phoma on varieties without double phoma resistance is clearly having an effect on green area. And light leaf spot is also widespread, with noticeable differences in infection levels between varieties with apparently similar middle-of-the-road resistance ratings.
“More than ever this season, spring agronomy needs to be geared to the development speeds of individual varieties, with those not carrying the highest levels of disease resistance likely to benefit from particularly careful management.”
In planning spring nutrition, Yara agronomist, Ian Matts underlined the importance of matching nitrogen applications for the canopy carefully to the amount of N already in the crop through Green Area Index (GAI) assessments. “Regardless of variety, February GAIs from comparative strips on our 3×3 site show crops receiving 20kg/ha of seedbed N, P and K have typically captured twice as much nitrogen in their canopies as those without autumn fertiliser,” he noted. “These as well as varietal differences need to be taken into account in spring N applications to achieve the optimum GAI of between 3.0-4.0 at mid-flowering. This is the way to ensure canopy structures that maximise light penetration and photosynthetic efficiency and minimise the production of thinner, weaker-stemmed plants with a higher risk of lodging.
“Reflecting on the importance of well-balanced OSR nutrition throughout the growing period, our research has shown yield benefits of around 0.5t/ha from including P, K and S with the spring N at all rates of nitrogen applied. We recommend employing an NPKS compound as the first spring dressing, followed by NS in a subsequent split to maintain the supply of sulphur through the season. An application of foliar N at the end of flowering has also proved very cost effective in increasing yields by extending the Green Area Duration. “Tissue testing is showing molybdenum and boron shortages in most crops this season,” Ian Matts added. “So a proprietary micro-nutrient mix included in the spray programme looks like being highly worthwhile for many too.”
Dose and timing
As far as the spray programme is concerned, BASF agronomy manager, Ruth Stanley stressed that product choice, dose rate and timing will need to be carefully matched to both crop development and the green area index for the most efficient and robust canopies. “With GAIs comfortably above 1.0, in many of this season’s crops they will need some decent plant growth regulation,” she suggested. “Our extensive lodging studies with ADAS have shown that even what most people would call a gentle lean at mid-seed fill can lead to yield losses of over 1t/ha through shading and reduced light interception.
“This can be guarded against by a timely stem extension application of the specialist PGR, Caryx (mepiquat chloride + metconazole) to reduce apical dominance. The much better-branched plant architecture it produces has also been found to increase seed numbers per square metre by almost 15 per cent and yields by around 0.5t/ha.
“Caryx is rate dependant,” said Ruth Stanley. “While 0.7-1.0-litres/ha is recommended for crops with GAIs of more than 0.8, this increases to 1.0-1.4-litres/ha where GAIs are 2.0 or more. It has a relatively wide application window – from the start of stem extension through to yellow bud. For the greatest value, though, it’s important not to apply the PGR too early or too late. “So, with crop growth and development varying as widely as it does this season, growers will need to keep a careful eye on individual crop growth stages as well as GAIs to make sure their applications are as well timed as possible. “Where early light leaf spot treatment has not been necessary, extra fungicide can always be added to Caryx. For varieties with lower levels of resistance, in particular, I would never advise delaying light leaf spot treatment to save on a spray pass.”