Survival of Lab Grown Calonectria pseudonaviculata Microsclerotia During Small-Scale Composting

Boxwood blight, caused by Calonectria pseudonaviculata, is a devastating fungal disease of Buxus spp., first observed in the United States in 2011. Due to the persistent nature of the produced microsclerotia, concern arose over the potential for compost to serve as a disease vector. Previous work demonstrated that C. pseudonaviculata is very stable at mesophilic temperatures, however, no previous work has evaluated C. pseudonaviculata during composting. Our objective was to evaluate the survival of C. pseudonaviculata microsclerotia after being composted for 24, 48, and 72 h at temperatures of 40, 50, and 60 °C. Composting was performed using a newly created bioreactor system, allowing for precise control of the composting process. In conjunction with the composting evaluations, the same temperature/time combinations were evaluated in incubators. While the pathogen survived 40 °C through 72 h in an incubator, compost survival was minimal, with only some survival observed at 24 h at the same temperature. We were able to determine that exposure to temperatures ≥50 °C for 24 h or longer, and that exposure in a composting system for 48 h or longer at 40 °C would kill the microsclerotia.