Success and Failures of Biofumigation with Brassicas

The use of Brassica species as green manure is a type of biofumigation involving the release of isothiocyanates, thiocyanates, nitriles or oxazolidinethiones that control multiple soil-borne problems. Biofumigation can be achieved by incorporating fresh plant material, seed meals, or dried plant material treated to preserve isothiocyanate activity or by using Brassica intercrops. Thus, Brassica residues can provide varying levels of pathogen control, either alone or when combined with other disinfestation methods. However, some recent studies indicate that the effectiveness of organic amendments including Brassica residues is variable and, in some cases, soil amendments with Brassica products can enhance disease severity. The negative effect of these amendments may result from increased pathogen inoculum potential when the substrate serves to sustain saprophytic growth of plant pathogens. Some examples of success and failure of the use of biofumigation against soil-borne pathogens and Brassica oil to control leaf diseases of vegetable crops are reported.