Dealing with fungicide resistance
5 Feb 2021
Dr Jon Helliwell, Business Development Manager
Every year BASF collects Septoria isolates from across the continent, as well as from the UK and Ireland and tests them to assess how the population is shifting in its sensitivity to the chemistry. In our blog today, we speak to Jonathan Helliwell at BASF to understand how we deal with fungicide resistance and protect new chemistry.
Our recent assessments have shown that in the UK there has been a further shift in lab sensitivity to Septoria recorded for SDHIs. The majority of this shift has come within isolates that are ‘moderately mutated’ – that is SDHIs still have a good level of performance against them. There have been no reported field failures, and the most severe H152R mutation remains at a low and largely unchanged level. SDHIs remain a key part of disease management strategies. When thinking about protecting SDHI chemistry into the future, there are some fundamental considerations that can be made to reduce the further sensitivity shifts:
- All commercial SDHIs are cross resistant, with mutations at the fungicide target site reducing sensitivity of the Septoria isolate to the SDHI molecule. Therefore, any reduction in sensitivity will impact all SDHIs, although the degree to which this occurs varies based on the intrinsic activity of the individual SDHI in question. Xemium® remains the strongest on Septoria.
- By applying a higher total loading of SDHI to a crop than necessary, selection pressure and therefore risk of resistance development is increased.
- Combining an SDHI with another strong mode of action will reduce selection pressure on the SDHI component of the mix.
2020 monitoring data has shown that the efficacy of conventional triazoles (including prothioconazole) has continued to shift in the UK. Revysol® sensitivity has remained stable, with high levels of in-field efficacy. Revysol® belongs to a new class of azoles, the isopropanol-azoles. The unique structural flexibility of the molecule allows it to bind more than 100 times stronger than conventional azoles to the target site on Septoria. This structural flexibility allows Revysol® to adapt to changes at the fungal target site, which combined with the unique binding power gives standout performance even in populations where conventional triazoles struggle. This is crucial, as we now face a new baseline for our UK Septoria population – one which consists of shifted strains and virtually no fully sensitive wildtype population.
Revysol® gives very reliable Septoria control against all known shifted strains in the field and, with CTL no longer available, the strength in combination with Xemium® sets it apart.
Practically, the strongest line of defence will always be to use a combination of the best tools available. Using strong genetics, partnered with fungicide programmes containing SDHIs combined with effective alternative modes of action including the strongest triazole, continues to be the optimum to minimise any further resistance shifts. Revysol® is an excellent resistance management partner to SDHIs and other modes of action. Combinations of Revysol® mixed with Xemium®, BASF’s best-in-class SDHI are synergistic, giving a greater level of control that you’d expect from their individual components.
However, it’s more important than ever to protect the chemistry that is available. Even though Revystar® XE has class-leading curative activity when required, applying it at the correct timing and at an appropriate dose is crucial. BASF will continue to routinely monitor populations across the UK and Europe, but as Septoria is a pathogen that will continually seek to out-manoeuvre growers, utilising every possible tool in the box is vital.
Revystar® XE and Revysol® are registered trademarks of BASF. Revystar® XE contains Revysol® and Xemium®. Revysol® contains mefentrifluconazole. Xemium® contains fluxapyroxad. Always read the label and product information before use. For further product information including warning phrases and symbols, you can refer to agricentre.basf.co.uk
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