Dissipation of Soil Fumigants From Soil Following Repeated Applications.

To achieve effective control of soilborne pathogens, a soil fumigant must move rapidly from the application site and distribute uniformly within the cultivated soil. Dissipation of pesticides in soil and occurrence of accelerated degradation following repeated applications is well known with many pesticides, but much less so with soil fumigants. The fate of various soil fumigants was studied in different agricultural soils following repeated applications of chloropicrin.  Fumigant dissipation reflected by ∑Concentration x Time (∑CxT) and half-life values varied widely among the tested soils. Methyl iodide (MI) had the slowest dissipation rate compared with other fumigants in all tested soils. Elimination of biotic agents by soil sterilization prior to MI application did not affect MI concentration in soil. Clay content and fumigant dose of chloropicrin, 1,3-dichloropropene and MI were significantly correlated. No significant correlations were found between soil properties and ∑CxT values following metam sodium and methyl bromide application.