Product label changes are being considered by the Pesticides Safety Directorate after trials suggested just two triazole fungicide actives gave more than the 80% control of Septoria tritici required for a label claim.
Only prothioconazole and epoxiconazole gave high levels of control of Septoria tritici in the four trials commissioned by PSD, ADAS fungicide expert Bill Clark exclusively told Farmers Weekly ahead of publication of the results at an Association of Applied Biologists conference yesterday (7 September).
Other triazole fungicides were “way off the pace,” he said. For example, tebuconazole gave only 27% control across the three English sites where disease pressure was high, and cyproconazole 30%.
“The bottom line is in high-risk septoria situations only epoxiconazole and prothioconazole would give adequate control if used alone.
“Many would argue [correctly] that triazoles are not used alone, but that is just concealing they are much weaker now.”
Indeed, the trials were commissioned by PSD after growing concern over the decline in control given by epoxiconazole in HGCA appropriate fungicide dose trials.
But unlike those trials where single applications are applied, two full rate applications of each product were applied in the PSD trials.
PSD would be considering carefully what action to take, if any, in the light of the results, the directorate’s David Richardson said.
The first step has been a meeting with the manufacturers on Tuesday (5 September) to discuss the results, where they were able to present their own data.
“From a regulatory point of view the options range from doing nothing to taking claims of [Septoria tritici] control off labels,” Mr Richardson said. But no product’s approval would be revoked as a result of the trials, he stressed.
Another, perhaps easier, choice would be to add a general statement to all azole labels regarding septoria control, he suggested.
“The key thing is to raise awareness of control problems, and for growers to focus on good disease strategies.”