Combinations of soil fumigants for methyl-bromide replacement.

The development programme synergistically combining dazomet and 1,3-dichloropropene at reduced dose rates for broad spectrum soil disinfestation was continued with the simultaneous application of dazomet and the potential soil fumigant dimethyl disulfide (DMDS). Combinations were compared to the separately applied fumigants in soil column experiments allowing comparison of treatments, soil conditions and dose rates. Efficacy over the depth profile in experimental soil columns was studied with packed soil buried target organisms: fungi, nematodes and seeds. It was shown that the combination of 20 g Basamid (98% dazomet) and 40 ml DMDS/m2, even at short fumigation period (1 week), under well controlled conditions performs very well both on the level of broad activity as on depth activity. Studied factors determining fumigant performance are: soil temperature, soil moisture content and the presence of organic matter. Finally, activity of this dazomet plus DMDS combination at reduced dose rates was tested on different phytopathogenic fungal targets as well as on a Trichoderma fungus. It was shown that weaker performance of full rate separately applied compounds could become compensated by simultaneous application at half of the recommended dose rates of each. Appropriate soil conditions were confirmed as well as the necessity to avoid high organic matter content in soil or to increase dose rate at high content for successful soil disinfestation. It is also emphasized that both methyl isothiocyanate (MITC), that is the active generated in soil from dazomet, and DMDS are naturally occurring compounds similar to the actives generated by 'bio-fumigation' practices. The advantage of synthetic generators is the better control upon effective dose rate.