Triazole fungicide limit proposed by Syngenta

Controversial proposals to limit the number of sprays to two of any single triazole fungicide active ingredient in a wheat disease control programme have been proposed by manufacturer Syngenta.

The stewardship proposal is attempting to prevent any loss of performance, says Syngenta’s Dave Ranner.

“The appearance of septoria strains which are more difficult to control with existing triazole choices was an unexpected development,” he points out. “There have been reports of less sensitive strains from the UK, Ireland and France. Our concern is for what might happen next.”

Syngenta’s suggestion is to limit the use of any one triazole to just two applications per season, rather than to restrict the total use of triazole chemistry, as was done with strobilurin fungicides once resistance to them was confirmed, he explains.

In practice, it means growers would be able to spray Opus (epoxiconazole), for example, at T1 and T2, while a second triazole not containing epoxiconazole would then have to be used at T0 and T3.

“As resistance and legislation start to bite, our view is that the use of a single triazole repeatedly in one growing season is unlikely to help the situation,” Mr Ranner says.

Syngenta also suggests including chlorothalonil with every application of triazole targeted at septoria in wheat.

“Mixtures are known to help delay the development of resistance and chlorothalonil is key for septoria control.”

The Arable Group (TAG) supports the idea of triazole stewardship, says David Parish. “A maximum of two sprays containing the same triazole will also be our recommendation for this coming season – and just one would be even better.”

The industry is dealing with a complicated and unknown story with septoria sensitivity, making it difficult to predict how the situation will develop, he explains.

“Where you have the ability to ring the changes and minimise repeat applications, it would seem sensible to do so. The important thing is not to jeopardise your disease control.”

Whether specific mutations to specific triazoles develop eventually remains to be seen, he says.

“The mutations we know about all react differently and not all of them impact on the field performance of fungicides. We also know that not all triazoles act the same.

“This chemistry is of enormous importance to cereal growers, so any action taken now to protect and enhance their life would seem a sensible approach.”

Proposals not supported by science 

 The science doesn’t support Syngenta’s proposals, Bill Clark, director of Broom’s Barn says.

“There’s no sense in it from a resistance management point of view.”

The two most widely-used triazoles – epoxiconazole and prothioconazole – are both still highly effective and do not select strongly for any of the mutations found in septoria populations to date, he explains.

“On that basis, why would it help to alternate or limit certain active ingredients?” he asks.

Although the use of alternate triazole active ingredients in 2010 fungicide programmes is also being promoted in Ireland, Mr Clark remains unconvinced.

“The only triazole which has had its field performance affected is tebuconazole, and that was due to a certain mutation, which neither epoxiconazole or prothioconazole select for,” he says.

He prefers the use of mixtures, which are known to delay the development of resistance.

“As far as growers are concerned, field performance is the critical factor. And we’re not seeing any loss of activity due to the presence of these septoria strains.”

 Syngenta triazole proposals 

Limit triazole active to two sprays per season

Attempt to prevent loss of performance

Controversial proposal

Resistance management unproven

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