Picture: By combining Amistar Opti with a triazole you hit disease with a three-pronged attack, says Syngenta product manager, Paul Varney.
A NEW solution to help growers combat resistance of the country's most damaging wheat disease to key fungicides will be available this season. As well as controlling all forms of the disease, including resistant strains, trials have shown it has also given substantial improvement in yield.
According to Syngenta's global fungicide resistance expert Professor Ulrich Gisi, resistance of Septoria tritici to strobilurin fungicides escalated from 31 to 71% in England last season and from 17 to 43% in Scotland. Moreover, cross-resistance exists across all strobilurins, he adds.
But equally concerning, research has shown the sensitivity of Septoria tritici to triazole fungicides, often relied on to partner strobilurins, has also started to shift.
"While a half rate triazole gave around 90% control of Septoria tritici between 1995 and 97, in 2003 it was only giving about 60%," explains Prof Gisi. "In the next few years, it is unknown to what level the sensitivity shift will evolve."
Against that, Prof Gisi says the good news is that because of the ability of strobilurins to boost yield in other ways, they still have a strong place. Also, mixing a strobilurin and triazole with the fungicide Bravo, which has a different mode of action, gives good disease control even if the frequency of resistance is high. It can also slow down the evolution of resistance, he adds.
"That can either be achieved by tank mixing a strobilurin + triazole + Bravo, or newly-approved Amistar Opti provides growers with the strobilurin Amistar already combined with Bravo in one product."
Syngenta product manager Paul Varney agrees and says new product Amistar Opti has been developed in direct response to the resistance problem. But as well as resistance management, it has been shown to boost yield in its own right.
"Even in resistant Septoria situations, strobilurins still add 0.3-0.5 t/ha to yield per application," says Mr Varney. "So they are very worthwhile. But growers do need to manage resistance.
"By combining Amistar and Bravo in a single co-formulation, it allows growers to take advantage of Amistar for maintaining green leaf area and controlling diseases such as take-all and rusts, but importantly gives back control of resistant Septoria tritici. It still needs mixing with a triazole for curative disease control but, vitally, it will help protect the triazole against further sensitivity shifts.
"In resistance trial plots, Amistar Opti has given an extra 2.5 t/ha yield compared with other strobilurins, worth an extra £185/ha margin over fungicide costs. Also, as a co-formulation it will be more cost-effective than simply tank mixing Amistar and Bravo and, with fewer packs to worry about, will help growers reduce any packaging waste."
The key timing for using Amistar Opti, believes Mr Varney, is at flag leaf (T2), with a follow up of Amistar + triazole on the ear (T3).
"This is because the ear and top two wheat leaves contribute approximately 90% of the yield, so are important to protect. Also, using strobilurins at these timings allows growers to make use of them against a wider range of diseases. Alternatively, where rust pressure is high, growers can use it earlier in the season at T1.
"By combining Amistar Opti with a triazole you hit disease with a three-pronged attack. In trial plots, adding Amistar has given an extra 0.85 t/ha yield over a triazole alone, while adding Bravo on top has added a further 0.77 t/ha."
