The Potential of Utilizing Brassicaceae Green Manure for Control of Soil-Borne Pests and Weeds.

A high proportion of irrigated and intensive agricultural fruit and vegetable crops use synthetic soil fumigants prior to planting.  Common chemicals used in vegetable production include metam sodium, methyl iodide, and chloropicrin, which can be highly effective either when applied individually or in mixtures.    However, all these synthetic compounds are highly toxic, and their use could pose health concerns in areas where they are applied.  One possible alternative to using synthetic soil fumigants is to use Brassicaceae green manure crops (plow-down crops) which contain glucosinolates.  Glucosinolate breakdown products have been shown to have insecticidal, fungicidal, and herbicidal properties.  Glucosinolates, per se, are not toxic, but when mixed with water in the presence of myrosinase enzyme, they degrade into a number of toxic compounds including isothiocyanates and ionic thiocyanate.  Results from using Brassicaceae green manure crops have been inconsistent and unrepeatable.  Many believe this is a result of not applying a sufficient amount of glucosinolates to the soil at an appropriate time.  This study examines green manure biomass accumulation and glucosinolate content over time to determine optimum incorporation of plant tissue to maximize glucosinolate production per area.  In addition glasshouse assays examining the efficacy of green manure potential as herbicides are compared to Brassicaceae seed meal tissues.  Results from these studies will be discussed in relationship to use of green manures in organic production.