Farmers should hold their nerve and not increase azole or SDHI dose in an attempt to counter evolving fungicide insensitivity in septoria tritici.
No significant economic benefit from increasing azole or SDHI dose, above current farm practice, was found in a recent analysis of AHDB fungicide performance data by ADAS.
The analysis considered the benefit of the SDHI or azole applied in mixture with the fungicide chlorothalonil.
With performance of some fungicides declining, there is a strong motivation to do whatever is necessary to maintain septoria control.
However, the changing shape of dose-response curves showed that the extra yield from increasing azole or SDHI doses above current practice would not be enough to outweigh the cost of the extra fungicide.
Paul Gosling, who manages fungicide performance research at AHDB, said: “Septoria is becoming harder to control with azoles and SDHIs. However, farmers should not be tempted to increase rates, because this is not economic and would drive resistance faster.”
The economic calculations analysed all the AHDB septoria dose-response data up to 2018, and accounted for the effect of typical UK spray programmes and the need to be ‘risk-averse’ in treatment decisions.
Multisite-acting fungicides are not affected by resistance and remain key to maintaining septoria control and managing resistance.
Although chlorothalonil will still be available this season, the industry needs to look at the potential of other multisites that have activity against septoria.
AHDB, in partnership with the Fungicide Resistance Action Group (FRAG-UK), monitors the evolving resistance situation and provides the industry with the guidance to ensure disease control while minimising selection for resistance.