P-127 - DMI fungicide sensitivity monitoring of Cercospora beticola across Germany since 2014

Cercospora leaf spot (CLS) on sugar beet is caused by the ascomycete pathogen Cercospora beticola. Until recently, quinone-outside inhibitors (QoIs) and demethylation inhibitors (DMIs) were the primary classes used for preventing CLS in Europe, but effective management of the disease with chemical fungicides has decreased since 2012. The G143A mutation in cytochrome b of C. beticola led to resistance to QoIs and resulted in heavier reliance on DMIs. This has generated the need for DMI sensitivity monitoring in Germany. In our study, we assessed DMI sensitivity of >2,200 monosporic C. beticola isolates using a microtiter assay.  Here, we summarize data from the last decade tracking changes in DMI sensitivity over time and across different growing regions in Germany and across various DMI active ingredients. One aspect of our findings is that the geometric mean of EC50 values for difenoconazole and epoxiconazole has increased over time, whereas the highest EC50 value has remained fairly stable throughout recent years. We observed a positive correlation between difenoconazole and mefentrifluconazole, and between cyproconazole and epoxiconazole EC50 values. Notably, states such as Hessen and North Rhine-Westphalia have experienced higher EC50 values compared to other growing regions. Similar sensitivity patterns have been observed in other fungal pathogens exposed to prolonged DMI fungicide use. While predicting future resistance dynamics remains complex, ongoing surveillance and updated sensitivity data provide critical insights for refining management strategies.