Dig those greens: plant medicine for your soil

The soil fumigant methyl bromide must be phased out by 2015. This is just one example of how greater environmental awareness is placing growing pressure on farmers to search for more environmentally friendly ways to combat pests. M ethyl bromide is one of the most effective ways to combat soil pathogens. There are synthetic fumigants that can replace it, but the trend against chemicals might see them banned in future too. Fortunately, Brassicas such as rapeseed, broccoli, cabbage, rocket and mustard are highly effective in combating some soil pathogens and if used correctly could be effective substitutes for synthetic fumigants. Jan Meyer, manager of pastures and forage at Hygrotech, explains that Brassicas have secondary metabolites in their cells which when activated can protect the plant against nematodes, disease-causing fungi, bacteria and so on. In some cases, farmers can exploit this characteristic by incorporating these crops – known as biofumigants – into the soil. N eil Kruger, technical marketing adviser to Hygrotech, points out that other plants also have these properties, but that in Brassicas the enzyme myrosinase converts glucosinolates into isothiocyanates, which are similar to the active ingredient in synthetic fumigants. Whereas synthetic fumigants have an adverse effect on all soil organisms, pathogenic or beneficial, biofumigants only affect and suppress harmful organisms while allowing most beneficial soil organisms to flourish. Incorporating them into the soil increases organic matter content, which improves the structure, nutrient recycling and water dynamics of the soil. Synthetic fumigants, on the other hand, have no soil-building properties – in fact by killing beneficial soil organisms they often have a negative impact on soil health. Paddy de Vries, marketing specialist for vegetables under protection at Hygrotech, warns that biofumigants should not be seen as a wonder cure but should always form part of a holistic pest-management strategy. “Using Brassicas to control soil pathogens cannot replace good agricultural practices like rotation programmes.” H ygrotech and other institutions are currently investigating which crops are most suitable as biofumigants and the most suitable production methods for these plants. Because the use of biofumigants is still relatively new in South Africa, Jan and Paddy advise producers to evaluate Nemat and Caliente mustard in their own production environment in trial strips, before embarking on full-scale incorporation of this system. Contact Paddy de Vries or Neil Kruger on (021) 881 3830; Jan Meyer on 083 372 5263; Adèle McLeod on (021) 808 4795, or e-mail [email protected]. |fw