Growth trials were used to screen 15 commercially composted products for disease suppressive properties. The composted products represented a broad range of single and mixed waste streams. Disease suppression was assessed by replacing 30% peat with compost and investigating the effects on the three pathosystems, Pythium ultimum with Brassica rapa, Phytophthora erythroseptica with Solanum lycopersicum and Fusarium oxysporum with Allium cepa. Of the 15 composts investigated, three were found to be phytotoxic when used at a 30% inclusion rate; this was attributed to a combination of instability and high salinity. Of the 12 composts tested, five were found to possess disease suppressive properties. However, only one composted material was suppressive to more than one pathosystem. Suppression was more frequent for the Pythiaceae pathogens which were suppressed in five trials, while F. oxysporum was suppressed once by a composted material which was also found to suppress P. erythroseptica. Principal component analysis was used to illustrate the similarity between composted materials based on the organic wastes streams used in their production and physicochemical characteristics. Composts with disease suppressive properties were found to be produced predominantly from biowastes, and to a lesser extent sewage sludge. Green wastes tended not to be associated with suppressive properties in the composts investigated in this trial. CT II International Symposium on Organic Greenhouse Horticulture, Avignon, France.
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