Evaluation of Host Defense Inducers for the Management of Boxwood Blight Caused by Calonectria pseudonaviculata in North Carolina

Boxwood blight, caused by the fungal pathogen Calonectria pseudonaviculata, has been reported in over 30 U.S. states and is a threat to boxwood production worldwide. Although considerable research has been conducted to evaluate the efficacy of conventional fungicides and cultural controls for this disease, the potential of host defense inducers remains largely unexplored. This study evaluated the effects of application method and frequency on managing boxwood blight in both container and field production systems in 2018 and 2019 at two locations in North Carolina. Actigard 50WG (acibenzolar- S-methyl) and LifeGard WG ( Bacillus mycoides isolate J) were applied as drench and foliar treatments to container-grown boxwoods artificially inoculated with C. pseudonaviculata and to field-grown boxwoods exposed to a natural inoculum. Drench applications of Actigard resulted in lower disease incidence than the untreated control plants under container production. High efficacy of Actigard was also observed under field production despite favorable environmental conditions for the development of boxwood blight. Application frequency did not affect disease for either of the tested host defense inducers in either production system. These findings support the integration of host defense inducers into cultural practice– and conventional fungicide–based management programs for boxwood blight.