Experts advise on triazole use in 2010

Their joint advice is contained in a newsletter published by the Rothamsted Research Association, and follows intense industry debate about fungicide use following the identification of septoria strains reportedly less sensitive to leading triazoles.

The four Rothamsted Research disease experts - Bill Clark, Hans Cools, Bart Fraaije and John Lucas - say azoles remain the foundation of all cereal fungicide programmes. But they warn while the shift in sensitivity in septoria appears to have stabilised in recent years, it is possible new resistance mechanisms could shift it again, so continued vigilance and use of anti-resistance strategies is required.

Limiting the use of triazoles is difficult, as they are key components throughout fungicide programmes, so they should be used in mixtures whenever possible, they advise.

Chlorothalonil (Bravo) is seen to play an important role but it has virtually no eradicant activity. And the new SDHI fungicides, such as bixafen and isopyrazam, although having some eradicant activity, will need to be used in mixtures with azoles.

“With shifts in sensitivity, field performance often begins to be affected when low doses are used. Higher doses are more effective, more versatile in terms of timing and persistence and allow flexibility in follow-up sprays,” the scientists conclude.

Their advice comes at a time when agchem manufacturers appear to be divided on approaches to managing the development of resistance to triazole fungicides.

Syngenta has recently proposed growers use a maximum of two sprays of any single triazole active ingredient in a fungicide programme, together with the inclusion of chlorothalonil (Bravo) with every application of triazole targeting septoria tritici in wheat.

Syngenta technical manager David Ranner says the recommendation is being made to minimise the chance of triazoles not working in future.

“We fully accept the performance of the best triazoles is still extremely robust in the field. But can we guarantee that’s going to be the case next year, in two and three years time? We don’t know, nobody knows.”

BASF is proposing no restrictions on the use of single active ingredients, advising instead that the use of mixtures of key fungicides is the optimum strategy. To limit azoles within a programme would require substitution with less effective modes of action, and hence reduced disease control and profitability for growers, says BASF fungicide manager Peter Hughes.

“Growers should continue to employ good resistance management practice, and as a priority include products in the programme with an alternative mode of action such as boscalid and / or chlorothalonil,” he adds.

Bayer CropScience’s Dr Alison Daniels says Bayer is fully supportive of the RRA advice.

More information visit www.rothra.org

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