How to reduce the use of fungicides to control septoria disease in wheat

For a long time, fungicides were the only solution to prevent the spread of septoria disease. However, their effectiveness is sometimes compromised by the emergence of strains that are resistant to these chemical methods. What good practices can be envisaged in these circumstances?

For a long time, fungicides were the only solution to prevent the spread of septoria disease. However, their effectiveness has been compromised for the past few years by the emergence of pathogen strains resistant to these chemical methods. It is possible to control Septoria tritici contamination but it requires a combination of various solutions. Choosing a variety tolerant to septoria disease can reduce parasite pressure and hence damage. However, this is only partially effective. There is no such thing as a variety resistant to every disease! Employing a diversity of mechanisms of action and active substances is probably one of the surest ways to slow down the selection of resistant septoria strains. Given the context, a combination of substances still effective against this disease is recommended, limiting their use to one single application of SDHI (bixafen, fluxapyroxad, penthiopyrade) per season.

Can any fungicide be used to eradicate septoria disease in wheat?

Are all means acceptable to eradicate septoria? No. Four main fungicide families are currently authorised, Qols (including strobilurins), DMIs (including triazoles), chloronitriles (including chlorothalonil) and SDHIs. But all active substances are meeting resistance. The first to be affected were strobilurins. But since the 1990s, a reduction in septoria sensitivity to triazoles has also been observed.

Some conventional solutions still work. These include a combination of triazoles + chlorothalonil at wheat stage T1 (1-2 node stage) or triazole + SDHI at wheat stage T2 (last leaf stage). However, new solutions are also available. These are perfectly appropriate for use in a septoria control strategy in combination with a triazole and/or chlorothalonil.

Septoria resistance to strobilurins

The first strains of septoria resistant to strobilurins were identified in Ireland in 2001, followed by the UK, France and Belgium in 2002. Despite being a new family of substances, it was not long before they all lost their effectiveness against septoria disease. The phenomenon was first noticed in northern France. In the space of a few months, it spread throughout the whole of the country. The reason resistance to strobilurins emerged so suddenly and became established so quickly is a mutation in the DNA of the fungus.

A reduction in sensitivity to triazoles

The evolution in the sensitivity of septoria disease to fungicides in the triazole family is more complex and more gradual. Studies show that the lower sensitivity of septoria strains to triazoles can be explained by several mutations and sometimes even a combination of mutations. It is therefore essential to alternate programmes with substances belonging to this family to prevent the extension of this type of resistance.

Chlorothalonil offers a broader-spectrum activity against septoria

Unlike the majority of other fungicides, chlorothalonil offers a broader spectrum of activity. It acts on several sites of the fungus. It is described as having a “multisite” action mechanism. It remains highly effective against septoria disease despite having been used for several decades to protect wheat. Chlorothalonil can therefore be an extremely useful ally to limit the development of strains resistant to other fungicides.

In septoria disease control in wheat, the implementation of good practices helps to limit the use of fungicides. Prevention remains the best method for managing the risk of development of this disease. Crop rotation, the choice of variety and optimisation of nutrition are all methods that should be incorporated into the good practices implemented. Contact us for more information!