Efficacy of a copper-based bactericide in controlling bacterial blight of grapevines caused by Xylophilus ampelinus

We investigated the efficacy of a microbial copper agent to protect against bacterial blight of grapevine caused by Xylophilus ampelinus from 2012 to 2014 in Hokkaido, Japan. A solution of the basic copper wettable powder sulfate was sprayed at 10-day intervals in two processing plots, using two application protocols: seven rounds of application immediately after leaf development and three or four applications at the initial onset of the disease. Due to the low disease incidence for the duration of the study, symptoms were only observed on leaves, not on spikes or fruits. The disease incidence in plots that were treated at the initial stage of the disease was significantly lower than in untreated plots. This protective effect improved as the number of applications was increased. After overwintering of these vines, X. ampelinus was detected in the axillary buds of untreated vines, but it was seldom detected in vines treated at the initial onset of the disease. Thus, the copper agent controlled the extent of infection during the year of treatment and reduced the quantity of bacteria surviving overwintering. Our findings indicate that three or four applications of the agent at the initial stage of the disease should be effective to prevent bacterial blight of grapevines.