First report of QoI resistance in Cercospora beticola in sugar beet in Japan

QoI fungicides have been an important tool for controlling Cercospora leaf spot (CLS) of sugar beet in Japan. In 2013, CLS control failed at an experimental plot in Okhotsk subprefecture of Hokkaido after the application of trifloxystrobin. Among isolates of Cercospora beticola, the causal agent of CLS, collected from this field were the first QoI-resistant strains found in Japan based on bioassays, culture assays and detection of G143A mutation in the cytochrome b gene. Additionally, our surveys of commercial fields in 2014–2015 revealed the widespread QoI resistance of C. beticola in Hokkaido.