Effect of films on dimethyl disulfide emissions, vertical distribution in soil and residues remaining after fumigation.

An improved understanding of the conditions that influence dimethyl disulfide (DMDS) emissions, distribution through the soil and residues remaining after treatment will help to optimise the use of this relatively new soil fumigant for the control of soil-borne pests and disease, and to improve the safety of DMDS use. Using soil columns in the laboratory, the cumulative emission of DMDS using doses of 40 and 80 g m-2 were, respectively, 74.8% and 68.9% with bare soil, 4.2% and 9.6% with polyethylene (PE) film, 0.02% and 0.2% with Totally Impermeable Film (TIF). Six hours after injection DMDS was detected mostly 5 cm below the surface and very little at 25 cm when used on bare soil, compared with much higher and similar concentrations of DMDS 5 and 25 cm deep when films were used. DMDS at the injection port exceeded 1 µg cm-3 for longer when a film was used instead of bare soil. The total DMDS soil residues remaining in the soil, as a percentage of the initial DMDS dose at 40 or 80 g m-2 were, respectively, 1.17 and 5.58 with TIF, 0.91 and 1.18 with PE, 0.47 and 0.47 with bare soil. DMDS rose rapidly upwards and escaped from bare soil, whereas PE or TIF significantly reduced DMDS emissions, retained elevated DMDS concentrations in the soil for longer and distributed them more uniformly in the soil. TIF performed better in these respects than PE. TIF also reduced the potential environmental impact of DMDS more than PE, especially at the higher dose.