Causal agent, biology and management of the leaf and stem disease of boxwood (Buxus spp.)

An outbreak of a boxwood disease was observed in Southern Ontario nurseries in 2008, but appears to have been present in Ontario for at least 10 years. From 2008 to 2010, over fungal 312 isolates were obtained from diseased samples. Eight major fungal morphotypes associated with the blight were identified with morphological and molecular techniques. Among them, only Volutella buxi successfully satisfied Koch's postulates, which confirmed it is the causal agent of boxwood blight. Wounds may be the major penetration points for V. buxi since non-wounded inoculated tissues did not become diseased. The Buxus cultivar 'Green Gem' was the most susceptible compared to 'Green Velvet', 'Green Mound', or 'Green Mountain'. ISSR markers revealed low genetic variation of V buxi between different cultivars and locations indicating asexual reproduction and probably a recent origin in Canada. Six fungicidal treatments showed strong preventive activity and some curative activity against Volutella blight.