P-317 - Duration of protection offered by fungicides against boxwood blight

Boxwood blight, caused by Calonectria pseudonaviculata (Cps), affects both nursery production and landscape boxwood plantings. The aim of this study was to estimate the duration of protection offered by combinations of fungicides with different modes of action on cultivars with low and high susceptibility. Buxus microphylla ‘Tide Hill’ and Buxus sinica var. insularis ‘Justin Brouwers’ plants were sprayed with TopBuxus; a systemic acquired resistance (SAR) product, Actigard; and a mixture of propiconazole and chlorothalonil in all six possible combinations. Fully expanded leaves were collected at 5, 12, 19, and 26-days after the plants were treated. The leaves were inoculated with approximately 200 Cps conidia in a 50µL drop. Infection and sporulation data were collected after 7 days of incubation at 25 °C and RH >95%. There were no significant differences between any of the treatment combinations for infection except when the SAR was applied alone. There were no significant differences observed between any treatments for sporulation. The factors cultivar (P< 0.0001 and P< 0.0001), treatment (P< 0.0001 and P=0.0002), days-post-treatment (DPT) (P< 0.0001 and P=0.0075), and interaction of cultivar and DPT (P=0.012 and 0.014) were significant on both infection and sporulation, respectively. All treatments provided a short duration, up to 12 days of protection against Cps infection for the highly susceptible cultivar whereas they provided significantly longer protection on the less susceptible cultivar, up to 26 days.