Adding prochloraz to a triazole fungicide programme failed to change the resistance profile of the septoria population in three TAG winter wheat trials, according to testing carried out by the French National Institute for Agricultural Research (INRA).
It suggests there is no point in adding prochloraz to fungicide programmes unless it has a favourable impact on gross margins, says Jim Orson, The Arable Group‘s technical director. “At the moment we don’t have the yield results to say whether there has been an impact on yields from adding prochloraz.”
Three varieties – Ambrosia, Alchemy and Solstice – were each treated with either a triazole-only fungicide programme or a triazole plus prochloraz in April (T1) and May (T2) at sites in Lincolnshire, Gloucestershire and Norfolk. A third treatment applied prochloraz only in March, April and May. Each was compared with an untreated control.
Resistance testing on septoria lesions on the youngest leaves at the end of the season showed that the prochloraz-only treatment did shift the septoria population so there were more septoria spores with low resistance to other triazoles at the end of the season, says Mr Orson.
But adding prochloraz to an already effective triazole programme of prothioconazole at T1 and epoxiconazole at T2 made no difference to the final resistance make-up of the population compared with where the triazoles alone were applied.
This means prochloraz needs to add something to the bottom line for it to be worthwhile, he says.
Trials in France have showed a slight shift towards susceptibility where prochloraz was added to lower doses of the triazole rather than when used alone, he says. “That’s work we haven’t done.”
But there is also a question that even if populations could be shifted, whether they would be maintained over winter in fields where that has been achieved, he adds. “At the moment it looks as though the practical application of this must be in doubt because of these issues.”
The good news was that the testing – funded by the Pesticides Safety Directorate – showed there was no selection for more resistant populations after treating with triazole fungicides, with the proportion of moderately resistant isolates remaining similar to untreated control.
The results also showed that adding a strobilurin to the triazole base programme also did not select further for triazole resistance, as was suspected to have occurred in France a few years ago.