The reports last season of a further shift in azole performance don’t appear to be as bad as some feared. That’s the conclusion drawn from Bayer CropScience’s 2014 plot data.
Even at a high pressure Septoria site such as Callow in Herefordshire, plots featuring azole + CTL at T1 performed as effectively as those with new-generation SDHIs.
What’s behind the result is timing says Bayer’s commercial technical manager Gareth Bubb. “The flag leaf is the most responsive timing and it is right that farmers target our most potent actives there. But it’s about setting that allimportant
spray up, and if leaves two and three are infected you’re likely to see transfer to the flag leaf. In such situations you’re relying on the effectiveness of a product like Aviator 235Xpro, and new-generation SDHIs should not be used as a ‘silver bullet’.
“Despite the Septoria pressure at Callow, plots were kept clean because we had effective protection of leaves two and three. I appreciate how difficult it can be to determine T1 timing as often leaf three emergence coincides with GS32 rather than GS31. The best method is to dissect the top three leaves and what you are looking for is leaf three almost fully emerged on the main stem,” he notes.
And he says it is worth the effort when you consider what is at stake. “You can easily lose 1 t/ha to Septoria and you’re relying on premium chemistry for curative action. With a T0 of tebuconazole + CTL followed by Proline275 + CTL at T1, our base four spray programme cost circa £100/ha and delivered a treated mean yield response of more than 7t/ha across the thirty varieties trialled. With wheat at £130/t the margin over input cost benefit was over £800/ha!” he points out.
It is worth remembering that azoles are still good protectants. “We have seen a gradual loss in curative performance but protectively they have stabilised. Robust doses of our primary azoles are still delivering effective levels of disease protection.
“When you combine an effective azole with a good surface protector such as CTL you’re getting unrivalled preventative performance. The T0 and T1 are really about protection which is why our recommendation of 0.4 L/ha Folicur + CTL followed by 0.55 L/ha Proline275 + CTL works so well.”
But Mr Bubb does concede SDHIs do have a place at the T1 timing in some situations. “If early season disease control has been compromised then the curative activity of an SDHI will help. But typically I would save Aviator 235Xpro until the yield responsive T2 timing and use the broad spectrum activity of Proline275 + CTL at T1.”