Oilseedrape growers are going to have to find new ways to tackle the increasing riskof light leaf Spot (LLS), with news that the active ingredient, flusilazole, isto be withdrawn from the market. One of the key solutions will be a switch toPlover (difenoconazole) with earlier proactive treatments ahead of diseaseoutbreaks to prevent infection, advised Syngenta technical manager, ChrisCharnock.
Hepointed out that while Plover had been primarily positioned for its particularstrength in phoma control in fungicide programmes, trials had consistentlyshown that it also offers good control of LLS. Research by Syngenta andindependent trials has shown early application of Plover when there is a riskof light leaf spot infection can provide good levels of control.
Growersand agronomist do need to be thinking and acting ahead of LLS infection, butthere is good opportunity to provide effective control. He advocated that inhigh risk situations which is the norm for Scotland and Northern England, orwhere LLS susceptible varieties are being grown the clear advice is to sprayat then four expanded leaf stage in the autumn, and to maintain applicationrate at 0.5 l/ha.
Independenttrials in the Scottish Borders demonstrated complete control of LLS by Ploverover the winter with two sprays at the 0.5 l/ha rate, compared with 35% diseasein the untreated crop by February. Metconazole and flusilazole mixtures in thetrial all resulted in continued disease activity over the winter and into thespring.
TheSRUC (formerly SAC) trial also highlighted the yield advantage of effective LLScontrol, with the two-spray Plover programme giving the highest yield of testedfungicides, at 4.49 t/ha a 25% increase over untreated. A Plover programme ata 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 marginat todays prices.
MrCharnock pointed out that climatic conditions and slow crop emergence in recentseasons, combined with the introduction of some popular new varieties withlower resistance to LLS, had all compounded the disease pressure and led to anincreased risk and incidence in eastern and southern counties. Risk forecastsfor LLS in the 2013 crop in eastern counties and the south west were more thandouble any of the previous three years, for example.
Hebelieved that one of the reasons that LLS had previously been less prevalent inthe south and east is that most crops would have already been treated forPhoma, in many instances with Plover, which was giving the broad spectrumcontrol of both diseases. Phoma treatments are typically less frequently usedor applied later in Scotland, resulting in more LLS being identified.
Theseasons where we have seen a higher incidence of LLS further south, have alsobeen the years when Phoma applications have been missed or were late; whichfurther reinforces the dual-action of the Plover treatments, he added.
MrCharnock also warned that making autumn applications of prothioconazole forLLS, or Phoma, could subsequently restrict growers fungicide options in thespring.
Underthe terms of the withdrawal of flusilazole, sales of all products containingthe active ingredient must end on 12 October 2013, with all stocks to be usedor legally disposed of by 12 October 2014.