Abstract
In recent years, there has been an outbreak of grapevine leaf blight caused by Pseudocercospora vitis in greenhouses in western Japan. Because quinone outside inhibitor (QoI) fungicides have been used frequently to control leaf blight and other diseases, we assumed that the spread of leaf blight was caused by the emergence of QoI-resistant strains. When mycelial disks were assayed for mycelial growth on medium containing azoxystrobin, the sensitivity of some isolates was not assayed correctly. When a mycelial suspension was used instead of mycelial discs, however, azoxystrobin sensitivity of those isolates was determined correctly. Of 106 isolates of P. vitis collected from 12 grapevine fields in Fukuoka Prefecture in 2007 through 2009 and assayed for QoI fungicide sensitivity, 97 isolates from 11 fields were resistant to azoxystrobin and 9 isolates from another field were sensitive. We evaluated tebuconazole and fenbuconazole for control of grapevine leaf blight caused by QoI-resistant fungi in two heated greenhouses and two greenhouses partially covered with plastic in 2009 and 2010. When tebuconazole, fenbuconazole or QoI fungicides was applied 2 or 3 times from the prebloom stage through the berry development stage, tebuconazole and fenbuconazole were each effective controlling grapevine leaf blight, but QoI fungicide treatments were not effective.
