AHDB experts tip on septoria resistance management

Answering 12 frequently asked questions on septoria management, the tips should help people strike a balance between good control within the season and efficacy protection across multiple seasons.

The information comes following a debate at the 2017 AHDB Agronomists’ Conference, which concluded that low resistance risk fungicide programmes must be adopted universally to prolong the efficacy of cereal chemistry.

Paul Gosling, who manages crop disease research at AHDB, said: “Everyone needs to take collective responsibility to manage fungicide resistance threats.

To bring extra clarity to the action required, we’ve worked with the Fungicide Resistance Action Group to cut through the science and provide easy-to-digest information that can be used straightaway.

“We started with septoria due to its status as a key wheat disease and the associated control challenges, particularly the long-term decline in azole efficacy and the early signs of a shift in sensitivity to SDHIs.”

The questions and answers cover a wide range of topics, including ways to reduce the need to spray and how to balance fungicide programmes.

Fungicide Futures' black and white answers to

resistance management questions:

1. Does what I do on my farm make a difference to resistance?

Yes – Poor practice can make septoria tritici more resistant in one season, so you will face a more resistant population next year. Collective action is required.

2. Can varietal resistance slow fungicide resistance against septoria tritici?

Yes – If it allows a less intensive fungicide programme to be used. It acts like an extra mixing partner.

3. Is it good resistance management to keep disease at a low level?

No – If disease is kept lower by more intensive use of fungicides.

Yes – If disease is reduced by cultural methods (eg resistant varieties and later sowing).

4. When an SDHI is used, how should it be protected?

The SDHI should be mixed with an azole dose of comparable efficacy and a multi-site.

5. Is it only useful to add a multi-site at early treatment timings, T0 and/or T1?

No – Multi-sites are useful to protect azoles and SDHIs at all spray timings.

6. Is it still worth using azoles against septoria tritici?

Yes – Although efficacy has reduced, epoxiconazole and prothioconazole still give good (50 to 60%) control in a protectant situation and are vital to protect SDHIs.

7. Is there cross-resistance between SDHIs?

Yes – There is a high level of cross-resistance, so mixing SDHIs is not a resistance management strategy.

8. Does a strobilurin contribute to a balanced mixture to manage septoria tritici if added to an SDHI?

No – Strobs have low activity against septoria tritici and do not protect the SDHI.

9. Can using an azole at T0 to control yellow rust make septoria tritici more resistant to azoles?

Yes – Selection for azole-resistant strains happens whenever an azole is used, even if septoria tritici is at low levels and is not the target of the spray. If rust is

the main target, a strobilurin is a good alternative.

10. Can using an azole at head treatment, T3, to control fusarium make septoria tritici more resistant to azoles?

Yes – Selection for azole-resistant strains happens whenever an azole is used, even if septoria tritici is at low levels and is not the target of the spray. Adding a

multi-site reduces risk.

11. Which is best, mixtures or alternation of different modes of action?

Both – Mixtures and alternation are both good strategies to slow resistance. Mixtures are better in a wider range of situations and are required for some modes of action.

12. Can alternating azoles help slow resistance against azoles?

Yes – Alternating azoles may have

a small beneficial effect.

* Fungicide Futures is a joint initiative between AHDB and the Fungicide Resistance Action Group UK (FRAG).