Plant Pathogen Eradication During Composting: A Literature Review

Abstract

The process of composting, when managed in such a way that adequate temperature conditions are achieved, can lead to significant reductions in the levels of many plant and human pathogens. When adequate pathogen reduction is achieved, it is possible to create a beneficial and safe product from waste materials that would otherwise be disposed of in a landfill or incinerator. Time and temperature conditions necessary for the eradication of various types of plant pathogens during composting were evaluated via a literature review. Varying time-temperature conditions have been suggested in the literature and by compost standards organizations in Europe to treat plant pathogens in compost. Literature data suggested conditions for the eradication of phytopathogens were compared with the time-temperatures specified by the Canadian Council of Ministers of the Environment (CCME) and US Environmental Protection Agency (USEPA) for human pathogens. Most bacterial plant pathogens and nematodes, and many fungi and fungus-like organisms (including the Oomycetes and Plasmodiophoromycetes) are likely to be eradicated if compost operations adhere to the human pathogen time-temperature guidelines set out by the CCME and USEPA. Other fungi and fungus-like phytopathogens, and a number of viruses are more heat resistant. Results in the literature have been inconsistent for some hardier species, with some studies showing eradication during composting and others finding that these same species were still viable in finished products. In general, most researchers agree that commercial-scale composting, if monitored and controlled properly, will likely eliminate most phytopathogens, with the exception of a few hardy viruses and fungi/fungus-like organisms such as tobacco mosaic virus, Fusarium oxysporum, and Plasmodiophora brassicae. The higher temperatures and longer exposure times suggested in European guidelines and standards are likely to be effective against a broader range of phytopathogens than the CCME and USEPA requirements. Phytopathogen inactivation in composting trials at different experimental scales was considered. Bench-scale time-temperature studies using pathogen suspensions or cultures on media often did not reliably predict what would happen in full-scale composting systems. If particular pathogens are of concern in a region, either pilot or full-scale studies should be done to evaluate their fate within the composting process used locally, or a more consistently predictive bench scale procedure should be developed.