TAG monitoring shows no further shift in Septoria tritici resistance
Results have just been received from a limited programme funded by the Pesticide Safety Directorate (PSD) to monitor the Septoria tritici resistance in England to DMI fungicides (triazoles and prochloraz) by the French National Institute for Agricultural Research (INRA).
Winter wheat varieties, Ambrosia, Alchemy and Solstice, established at The Arable Group (TAG) trials sites in Lincolnshire, Gloucestershire and Norfolk were treated with fungicides in March (T0), April (T1) and May (T2). Each of the varieties was treated with the following type of programmes: untreated control; triazole only; triazole + prochloraz; triazole + strobilurin; and prochloraz only. The septoria lesions on the youngest leaves at the end of the season were sent to INRA for resistance testing. The results received detailed the proportion of the septoria populations with the resistant phenotypes.
As in 2007, this year's populations comprised 100% resistant phenotypes with the majority being moderately resistant rather than low resistant types. The distribution of phenotypes in England is similar to that of Northern France.
The results showed that the programme of three applications of 315 g/ha prochloraz (in this case Poraz) alone selected for phenotypes less resistant to the triazoles. However, it was disappointing to note that the addition of 200 g/ha prochloraz to an already effective triazole based programme did not result in less resistant populations at the end of the season.
The results also showed that the addition of strobilurins did not select further for triazole resistance as was suspected to have occurred in France a few years ago. The most likely explanation is that S. tritici in the UK is now almost certain to be also resistant to the strobilurins so they would not have imposed a selective effect.
Their use would not have modified the profile of the populations.
Crucially, there was no evidence that commercial treatments further selected for more resistant phenotypes in 2008.
