2025 Volume 67 Pages 73-80
During fungicide sensitivity tests conducted on Mycovellosiella nattrassii isolates obtained from eggplants in Osaka Prefecture, Japan, between 2012 and 2018, variations in sensitivity among different fungicides were observed. Least isolates exhibited low sensitivity to azoxystrobin (QoI) and penthiopyrad (SDHI) from 2014 to 2022. In contrast, the proportion of isolates low sensitive to triflumizole (DMI) was high during the same period. In 2024, a majority of isolates demonstrated reduced sensitivity to triflumizole, fenarimol (DMI), myclobutanil (DMI), azoxystrobin, kresoxim-methyl (QoI), penthiopyrad, and isopyrazam (SDHI). However, they remained sensitive to difenoconazole (DMI), pyribencarb (QoI), pyraziflumid (SDHI), and boscalid (SDHI). These results indicate that M. nattrassii isolates in Osaka Prefecture are predominantly characterized by reduced sensitivity to triflumizole, azoxystrobin, penthiopyrad, and isopyrazam. Furthermore, an analysis of fungicide application history revealed that fungicides with reduced efficacy were frequently applied across multiple fields. To mitigate the risk of developing fungicide-resistant M. nattrassii isolates, it is crucial to incorporate fungicides with multi-site modes of action, such as chlorothalonil and iminoctadine albesilate, which are considered to have a low resistance risk, for preventive management. Additionally, in cases where fungicide-resistant isolates are detected, it is essential to integrate into the rotation fungicides that have not yet exhibited a decline in efficacy.
