Apply best practice to stifle septoria
The difficulty in controlling cereal pathogens should not be underestimated. These organisms are complex and found ways to survive in the wild long before we decided we didn't want them in our cultivated fields.
Part of any pathogen's survival mechanisms is to change in response to an outside influence that stops it developing and reproducing. These outside influences could be cold, wet conditions, change of cultivar or the application of a fungicide.
Fungicides, once discovered and introduced, have a defined life of practical use before the pathogen develops ways around the fungicide's mode of action. The usefulness of any fungicide is dependent on how often it is used and how it controls the pathogen, ie a fungicide relying on one mode of action will have a shorter life than one which controls the pathogen in several different ways (Strobilurins versus Chlorothalonil).
As an example, if a fungicide had a life cycle of, say, 40 applications, then if it was applied on average three times a year, its useful life in the field would be around 13-14 years.
Septoria continues as a moving target and it appears the pathogen has shifted again this year. Oak Park duo Dr Stephen Kildea and Dr Eugene O'Sullivan have been monitoring changes in septoria populations for the past few years and they were among the first scientists to spot changes and identify trends in septoria development.
The genetic trends that occurred over this period established that septoria had developed mechanisms to tolerate more fungicide (before, the fungicide controlled them) and these strains have been classed as mutations (S524T, V136A, Y461S).
The mutations make these septoria strains harder to kill (or insensitive) by prothioconazole and epoxiconazole, therefore both these fungicides are grouped into Group 1-type triazoles. However, these septoria strains are easily controlled with both tebuconazole and metconazole (Group 2).