Composting Effect on Three Fungal Pathogens Affecting Elm Trees in Edmonton, Alberta

Abstract

The City of Edmonton, Alberta, produces compost from a mix of wood chips and biosolids at its aerated static pile composting facility. A portion of the wood comes from the City's Parks Branch, which supplies clean wood waste to the composter, and sends wood known to be diseased to landfill. However, wood from other wood suppliers is not necessarily screened, allowing the possibility that diseased wood might still be processed. It was of interest to determine the fate of some important Edmonton-area plant disease organisms during composting, in order to determine if infested wood actually needs to be diverted away from the composter. The current study focused on the fate of three fungi: Dothiorella ulmi; Verticillium dahliae; and V. albo-atrum. Wood chips inoculated with the three organisms of interest were placed into a newly constructed aerated static pile at various locations. The chips were retrieved during the first active composting stage and tested for pathogen survival. At locations where temperatures exceeded 40°C, all three pathogens were inactivated. However, survival of fungi was observed in cooler zones of the pile (e.g. near the surface). It is expected that mixing in subsequent stages of composting will move all material into the high-temperature zones.