The use of metam sodium (MS) has exceeded methyl bromide (MB) for soil fumigation and consistently ranks third among all pesticides used in the USA. However, several field trials aimed at evaluating the efficacy of MS have resulted in inconsistent pest-pathogen control. The declining efficacy of MS may be attributed to changes in the efficiency of MITC generation (MITC results from transformation of MS in soil) and/or changes in soil degradation. Changes in the generation and degradation of MITC in soil after application of MS were evaluated for soils with, and without, a history of fumigant use. Maintaining a high fumigant concentration in soils is imperative for achieving sufficient pest control. The soil MITC concentration was mainly affected by temperature and soil moisture. Rate constants and half-life values for of the generation and degradation of MITC will be presented.

Keywords: Metam sodium, methyl isothiocyanate, methyl bromide and half-life.