Protection of Boxwood Crops from Infection by <i>Calonectria pseudonaviculata</i> Under Controlled Environments and in Production Fields

Chemical protection has been a key component of boxwood blight (Calonectria pseudonaviculata, Cps) management programs, but each application of fungicides only protects the iconic evergreen landscape plant for 2 to 3 weeks at best. The objective of this study was to evaluate the potential of six film-forming anti-desiccant products – Anti-Stress 2000, AquaLock, Moisture-Loc, TransFilm, Vapor Gard, and Wilt-Pruf – for managing boxwood blight in lab experiments and in production fields. In lab experiments with container-grown Buxus sempervirens ‘Justin Brouwers’, TransFilm, Vapor Gard, and Wilt-Pruf consistently outperformed the other three products in suppressing Cps infection, sporulation and spore release. Specifically, these three top performers reduced blight incidence by ≥90.7% when they were applied 1 day before plants were inoculated with Cps. Likewise, they reduced conidial count by ≥76.1% when applied 6 days after inoculation. Both Wilt-Pruf and TransFilm provided significant but lesser degrees of protection to field grown boxwood crops in western North Carolina compared to their performance in the lab experiments. Comparatively, Wilf-Pruf had more consistent field performance than TransFilm. TransFilm protected B. sempervirens (“American”) only when applied monthly and B. sempervirens ‘Vardar Valley’ only when applied every 3 months. Wilt-Pruf protected both boxwood crops both at the monthly and 3-month application intervals.