The AHDB Agronomy Conference raised a slight worry over SDHI septoria shifts and possible cross-resistance with two leading actives, pydiflumetofen (Miravis Plus) and isoflucypram (Vimoy).
It follows laboratory tests by Niab that showed some cases of increased insensitivity to pydiflumetofen and isoflucypram. It is a small number of samples, and ADAS researcher Dr Jonathan Blake stressed that there has been no change in field performance, where both are applied with mixture partners.
He sees it as a warning shot. Late season sampling revealed some isolates with reduced sensitivity to pydiflumetofen and isoflucypram. “It is only a small population but it is a little bit of a concern,” he said.
He also noted that pydiflumetofen and isoflucypram appear to select similarly. “Where we see sensitivity or insensitivity with one, we see it with the other. It isn’t a great surprise, both are SDHIs,” he added.
Jonathan believes some new mutant combinations could be occurring, what is unknown is whether any will suffer a fitness penalty.
What is known is that SDHI resistance is becoming more complex, with double mutants and new field mutations emerging. It highlights that selection for insensitivity to SDHIs can occur.
Aside from the isolated incidences of reduced sensitivity, ADAS fungicide performance trials showed both pydiflumetofen and isoflucypram are working well and providing a level of eradicant activity. In straight protective trials, pydiflumetofen was a little ahead of fenpicoxamid, and both have the edge over isoflucypram and mefentrifluconazole. But he assured all were working well as protectants and some way ahead of ‘benchmarks’, prothioconazole and folpet.
When it came to mixtures, Jonathan presented data using Univoq (fenpicoxamid + prothioconazole) and Jessico Fusion (fenpicoxamid + isoflucypram). Again, both provided effective levels of protection.
For him it is another reminder of the importance of using differing modes of action in mixtures and across the programme, including the use of multisites for septoria.
“If we can avoid the repeated use of the same mode of action where possible. I’m confident we can increase the effective life of these at-risk actives and maintain field efficacy,” he noted.
