Recent identification of strains of septoria with reduced sensitivity to SDHIs means growers must redouble their efforts to use fungicides carefully to maximise returns and minimise further resistance risk, says a leading agronomist.
It would be both a big gamble and a false economy not to deploy a robust fungicide programme this year. That is according to ProCam technical director Tudor Dawkins, who says: “Complacency is not an option.
Although only a few isolates have been detected with reduced sensitivity to SDHI chemistry, history suggests it’s only a matter of time before these could establish as a major component of the UK’s septoria populations.
“With 2016 also shaping up to be a high disease pressure year, we need to use all the tools in the box to protect yield and to ensure a successful outcome, especially with the current commodity prices.”
Cutting back could not only result in poorer disease control but also significantly reduced yields, Dr Dawkins says.
“The best means of limiting development of resistance is to mix modes of action. The use of all the available actives, with contrasting modes of action, is an essential component for success.
“ProCam trials have shown using triazoles with chlorothalonil at T0 is a key part of the programme. Even the inclusion of cyflufenamid, where mildew is present, has helped with septoria control as a side benefit.”
Selecting the right triazoles is important so populations are not ‘conditioned’ to adverse selection pressure to the ones needed later, he adds.
“Both tebuconazole and prochloraz have a role to play at T0 in association with chlorothalonil.
“In years of high disease pressure such as 2014 we saw about 1t/ha added to the final yield from adopting this approach and this year is looking very similar.”
Rusts are well established in some crops so addressing this disease at this time is also important. Good responses from using triazoles and or strobs such as tebuconazole and pyraclostrobin have been seen in ProCam trials, he says.
“The emergence of a new race of yellow rust (Kranich race), which may affect the resilience of the more resistant varieties, needs to be watched but control is still possible with existing chemistry.”
Building a robust T1 is a prerequisite especially with the levels of disease out there this spring, he advises.
"The best means of limiting development of resistance is to mix modes of action" - Tudor Dawkins
“Triazoles, SDHIs and chlorothalonil all work best in a preventative role. We can get some help with a little curative action from SDHIs, but building a ‘firewall’ to prevent septoria gaining a hold at this stage should be the objective.
“We need everything to work together to protect the chemistry.”
T2 mixtures must be designed to protect the important yield-generating leaves and ProCam trials have again demonstrated the benefits of using triazoles, strobs and SDHIs in combination to achieve this, says Dr Dawkins.
“If disease pressure is less - as it was in 2015 - it is better to fine tune doses at this stage rather than drop actives out of the programme altogether.”
A key component of any successful programme is playing to the strengths of the chemistry used and using it all to protect it for the future, he believes.
“Preventative strategies are essential - use as many modes of action as you can, make sure timings are spot-on and don’t stretch the intervals between sprays.
“Strobs, such as pyraclostrobin can still bring benefits such as reduction in vigour of the septoria pathogen through inhibition of spore germ tube development.
“Triazoles still have valuable preventative activity, remaining very effective against rusts, and chlorothalonil brings significant protectant activity.”
Comparing the contrasting years of 2014 with 2015 highlights that fungicide strategy need not change too much from year to year, he concludes.
“In 2014, ProCam fungicide programmes delivered a 3:1 return - for every £1 spent, £3 were returned. Last year with lower disease pressure, many of our trials gave a 2:1 return.”