Oilseed rape growers are going to have to find new ways to tackle the increasing risk of Light Leaf Spot (LLS), with news that the active ingredient, flusilazole, is to be withdrawn from the market this autumn. One of the key solutions will be a switch to Plover (difenoconazole) - with earlier proactive treatments ahead of disease outbreaks to prevent infection, advised Syngenta Technical Manager, Chris Charnock.
He pointed out that whilst Plover had been primarily positioned for its particular strength in Phoma control in fungicide programmes, trials had consistently shown that it also offers good control of LLS. “Research by Syngenta and independent trials has shown early application of Plover when there is a risk of Light Leaf Spot infection can provide good levels of control.
“Growers and agronomist do need to be thinking and acting ahead of LLS infection, but there is good opportunity to provide effective control.” He advocated that in high risk situations - which is the norm for Scotland and Northern England, or where LLS susceptible varieties are being grown - the clear advice is to spray at then four expanded leaf stage in the autumn, and to maintain application rate at 0.5 l/ha.
Independent trials in the Scottish Borders demonstrated complete control of LLS by Plover over the winter with two sprays at the 0.5 l/ha rate, compared to 35% disease in the untreated crop by February. Metconazole and flusilazole mixtures in the trial all resulted in continued disease activity over the winter and into the spring.
The SRUC (formerly SAC) trial also highlighted the yield advantage of effective LLS control, with the two-spray Plover programme giving the highest yield of tested fungicides, at 4.49 t/ha - a 25% increase over untreated. A Plover programme at a lower 0.25 l/ha did still achieve 90% LLS control and a yield of 4.18 t/ha, but the higher 0.5 l/ha rate would have delivered an additional £94/ha margin at today’s prices.
Mr Charnock pointed out that climatic conditions and slow crop emergence in recent seasons, combined with the introduction of some popular new varieties with lower resistance to LLS, had all compounded the disease pressure and led to an increased risk and incidence in eastern and southern counties. Risk forecasts for LLS in the 2013 crop in eastern counties and the south west were more than double any of the previous three years, for example.
He believed that one of the reasons that LLS had previously been less prevalent in the south and east is that most crops would have already been treated for Phoma, in many instances with Plover, which was giving the broad spectrum control of both diseases. Phoma treatments are typically less frequently used or applied later in Scotland, resulting in more LLS being identified.
“The seasons where we have seen a higher incidence of LLS further south, have also been the years when Phoma applications have been missed or were late; which further reinforces the dual-action of the Plover treatments,” he added.
Mr Charnock also warned that making autumn applications of prothioconazole for LLS, or Phoma, could subsequently restrict growers’ fungicide options in the spring.
Under the terms of the withdrawal of flusilazole, sales of all products containing the active ingredient must end on 12 October 2013, with all stocks to be used or legally disposed of by 12 October 2014.
