With Sclerotinia posing a potentially devastating threat to oilseed rape growers, farmers are being advised to adapt their fungicide programmes to ensure protection throughout the flowering period, and to choose products with additional benefits, such as green leaf retention.
Sclerotinia can have a devastating hit on oilseed rape yields in a high pressure situation. It is more than a decade since the last serious national outbreak, but there are still reported incidences every year.
Where growers have a history of sclerotinia incidence on-farm, particularly when the season conspires to create disease pressure – typically with warm, wet weather through the flowering period – Syngenta OSR field technical manager Georgina Wood suggests growers will benefit from additional advantages of green leaf retention with Amistar, alongside its disease control.
“This season the greening effect could be particularly important to help crops recover from the impacts of cabbage stem flea beetle larvae damage,” she advised iOSR growers. “In many instances crops have shed large numbers of leaves where the petioles have been damaged.
“They will now be reliant on compensatory new growth, to capture sunlight and fill seeds with oil.”
Furthermore, Georgina warned that the larvae damage has created widespread variability between plants, which is anticipated to lead to an extended flowering period.
NIAB has already warned growers of the protracted flowering period, which it reports may need a two or even three spray disease control strategy.
With a target 6000 to 8000 pods per m2, Georgina pointed out that OSR seed yield is determined by the amount of photosynthesis carried out by the crop during a 19 - 25 day period after mid-flowering, with green leaf the primary source of energy for seed fill.
ADAS trials have shown that a single Amistar application can maintain an additional 0.5 GAI 10 days after end of flowering and still 0.25 greater GAI 20 days later.
“Fungicide application timing is going to be important this season,” she suggested.
“If sclerotinia risk rises, then the conventional early to mid-flowering prevention will be crucial. But growers will also still likely gain from later applications, targeted at healthy green leaf retention and preventing leaf spot infections.”
In both instances, she believes the greening effect of Amistar will boost the essential oil content of seed and overall returns for growers.
Cabbage stem flea beetle continue to be a major concern for iOSR growers.
In Cambridgeshire, Ian Lutey reported infestations of up to 25 larvae per plant had stunted growth of some plants, leading to risk of an extended flowering period with the mixed growth stages.
With the main stems appearing relatively unscathed by larvae damage, even on stunted plants, he is hoping hybrid varieties can still compensate and put on sufficient growth to yield well.
Oilseed rape crops that were mown down or grazed off over the winter, in an effort to remove high populations of CSFB larvae in leaf petioles, appear to have recovered remarkably well.
On the iOSR Focus Site in Suffolk, Syngenta Field Technical Manager, Georgina Wood, reported virtually no losses in plant numbers from one or two passes with the mower, with good levels of initial regrowth triggered by early spring conditions.
And in Norfolk, where iOSR grower, Chris Eglington, had grazed sheep for six days across half a field in January, recovery was remarkably strong.
By early April, with the grazed portion at early stem extension, it was still significantly behind the ungrazed crop – where some plants were breaking into flower.
However, the crop was extremely consistent and vigorous. The result in terms of CSFB larvae present, and the resulting yield, could prove one of the most enlightening advances in managing a pest that threatens future viability of OSR cropping for many growers.