Soil fumigation with methyl bromide or other compounds was used in certain high-value crops to control a wide range of soil borne pests including many root and foliar disease pathogens, plant parasitic nematodes, and weed seeds or vegetative propagules. Soil fumigants are broad-spectrum biocides; thus they are usually used “preplant” and are applied several weeks or months before the crop is planted to reduce the chance of crop injury.
Pest control efficacy depends on the organism receiving a sufficient concentration-time (CT) exposure to the fumigant. Fumigants are subject to a number of dissipation processes including chemical and microbial degradation to non-toxic metabolites, partitioning into soil organic matter or clay particles, off-gassing or emission to the atmosphere. Effective CT values can be reached through high concentrations for short periods of time or through lower concentrations for longer periods of time.
Application of soil fumigants in California, Oregon, and Washington is a highly-regulated process and is typically done by professionally trained and licensed applicators rather than by individual growers.