RESEARCHERS ARE beginning to question the scientific basis for restricting the use of triazoles in controlling disease, especially in wheat.

This week, both Rothamsted Research and the SAC have disputed recent advice recommending a restriction in the number of triazole applications to wheat crops for septoria control.

Citing the recommendations for a two-spray limit as scientifically unfounded, a disappointed Bill Clark, a director at Rothamsted’s Brooms Barn centre, confirms there is no change to the recommendations for triazole use to control septoria tritici for the 2010 season. That is despite growing evidence that restrictions could be relaxed.

In a publication, issued this week by Rothamsted Research, which is led by Mr Clark, the advice is: “The use of azoles, such as epoxiconazole, is to continue to use the chemistry responsibly, for example in mixtures with other modes of action and to continue using robust dose rates.”

From the Fungicide Resistance Action Group (FRAG), the UK position also remains unchanged – ie no restrictions on the number of azole applications in the programme, but azoles should not be used alone.

SAC’s Dr Fiona Burnett also pointed out: “While there is evidence that some azoles select differentially for resistance mutations, of the two most effective azoles that growers use (epoxiconazole and prothioconazole) there is no evidence of any differential effect in selection which would give any advantage to alternating them in terms of either product stewardship or efficacy.

“I have an additional concern that by attempting to alternate with other azoles of poorer efficacy, disease control might be compromised, which may leave growers attempting to control high levels of disease at the next spray timing. This will potentially have a far greater selection pressure to resistance than any advantage gained from azole alternation,” she said.

Commenting on what has become a heated debate, Peter Hughes, BASF’s cereal fungicide product manager, added: “BASF’s findings and guidelines for the use of triazoles concurs with Rothamsted’s and SAC’s stance. Our own latest resistance monitoring in the UK shows that there has been no significant shift of septoria tritici sensitivity to epoxiconazole and tested isolates remain within the normal range.”

He added: “The key is not limiting azole use – it is ensuring that good resistance management practices are adhered to, so the priority is to include products in the programme with an alternative mode of action to the azole partner such as boscalid and/or chlorothalonil.”