Soil behaviour of sulfur natural fumigants used as methyl bromide substitutes

Abstract

Methyl bromide is the most widely used and most effective fumigant and is used extensively for soil fumigation. According to the Montreal Protocol of 1991, methyl bromide is categorised as an ozone-depleting chemical and its use is prohibited from 2005.

Many substitutes, such as methyl isothiocyanate and methyl iodide, are not applied as widely as methyl bromide. Moreover, crushed Alliumspp. plants (garlic, leek and onion) produce thiosulfinates (Ti, R–S–SO–R′) and related compounds like disulfides, which have the same pesticide activity as methyl bromide. Therefore Allium tissues or extracts can be used in biological control and Integrated Pest Management in agriculture.

The successful application of these compounds, and Allium tissues and extracts, for biological soil disinfection requires more specific knowledge regarding their subsequent fate in the soil. To obtain this, appropriate analytical methods using IR spectroscopy, SPME (solid-phase micro-extraction) and GC-MS techniques were developed and applied in the laboratory on pure compounds and on Allium tissues or extracts.

The experiments revealed that thiosulfintes are stable in the atmosphere but in soil they are rapidly degraded into disulfides, which are very stable in soil. For that reason and for their general pesticide effect, disulfides are a promising alternative to methyl bromide.

Keywords:

• Thiosulfinates
• Disulfides
• Allium
• Soil fumigant
• GC-MS
• IR