With the first case of septoria resistance to SDHIs recently confirmed in Ireland
With the first case of septoria resistance to SDHIs recently confirmed in Ireland, and winter weather conditions to date creating the ‘perfect storm’ for septoria infection this spring, multi-site chemistry will play a key role in this season’s fungicide programmes on wheat, says a specialist.
That is the advice from Adama Agricultural Solutions’ cereal fungicides technical specialist Andy Bailey, who also warns of the moral responsibility growers face in terms of limiting future SDHI resistance.
“This winter’s mild temperatures and record rainfall levels have resulted in lush crops and created the perfect over-winter conditions for diseases such as septoria and rusts to flourish,” he explains.
“High levels of septoria infection are already present on the lower leaves of many crops. If the persistent and heavy rainfall that has dogged the early growing season continues into the spring, this will enable the disease to spread rapidly via rain splash movement.
“Wet weather in March and April will extend the period of susceptibility by allowing fresh infections to take hold in upper leaves after stem extension. By this stage, the yield potential of many crops will have already been eroded and growers will be left chasing the disease.
“Getting this year’s crop protection tactics off to a good start by treating crops with an early programme of sprays is therefore essential,” he adds.
But Mr Bailey warns against the assumption that last year’s successful fungicide programme will work again this year. “There’s no room for complacency this year as we’re dealing with a different set of conditions and need to plan accordingly to provide crops with effective protection. “At this stage it certainly justifies the need for a T0 (typically azole + multi-site) followed at T1 by a robust azole + SDHI + multi-site mixture.”
A structured programme
Mr Bailey is encouraging growers to think carefully about how to structure their crop protection programme. “With field resistance to SDHIs confirmed in Ireland, growers can no longer rely on that technology alone to provide adequate protection. They also need to think, not just of this year’s crop, but also of subsequent harvests.
“Over reliance on the SDHIs without adequate protection will only increase the resistance risk. And with no new modes of protection in the pipeline and increasing regulatory pressures threatening the restriction and/or removal of many active ingredients, we could be looking at a scarcity of effective crop protection products in future years.
“Growers therefore have a moral responsibility to protect and prolong the efficacy and lifespan of existing products by further use of alternative modes of protection, namely the multi-sites.”
The industry has to move on from relying on azoles and SDHIs alone, Mr Bailey suggests. “Azoles still provide some benefit, but they are no longer fully effective as curative products. In fact, trials have shown that the preventative effect of azoles has reduced by 20 per cent over the past 10 years, while their curative efficacy has fallen by a huge 60 per cent or more.
“We now rely heavily on the SDHIs, particularly for curative activity due to the steady decline of the azoles, so it’s vital to extend their effective lifespan as long as possible.”
Mr Bailey recommends the inclusion of multi-site products for this year’s crop protection programme. “Stacking products is recognised as the most effective method of crop protection,” he says. “But it is important when using a multi-site chemistry to ensure that it doesn’t impact on triazole uptake. To get the best results, ensure that a multi-site active – such as folpet which doesn’t affect triazoles – is applied prior to stem extension at T0 and again at T1 to protect the newly emerged leaf 3. If spring disease pressures turn out to be as high as predicted, also apply folpet at T2 to combat fresh and spreading infections.”
Products such as Phoenix (straight folpet) and Manitoba (folpet + epoxiconazole) provide three stages of protection and are less susceptible to resistant mutations. “They are more robust and, as such, are vital to prolonging the role of azoles and SDHIs. New research indicates that including folpet-type products can reverse the effects of selection pressure making subsequent septoria infections more sensitive to epoxiconazole for example. This can give greater longevity and protection efficacy for current and future crops. Further research is evaluating similar effects with other triazoles and SDHIs.”
Mr Bailey recommends that growers consider the importance of an integrated management approach to tackle future septoria pressures. “Varietal selection, delayed drilling and fungicide programme selection should all be considered as part of an holistic approach to septoria management. It’s too late for varietal selection and drilling date to affect this year’s crop but it always pays to plan ahead for future seasons.”