Improvement of methyl bromide soil disinfestation and avoidance of side-effects

• Published in: Dissertationes de Agricultura (Belgium) no. 252
• Main Author: Wambeke, E. van
• Format: Publication
• Language: English
• Published: Leuven (Belgium) KULFLTB 01.04.1994
• Subjects: BROMURE DE METHYLE; BROMURO DE METILO; CUBRIMIENTO DEL SUELO; DESINTOXICACION; DETOXIFICATION; DIFFUSION; DIFUSION; EFECTOS RESIDUALES; EFFET RESIDUEL; EXPERIMENTACION; EXPERIMENTATION; FITOTOXICIDAD; FUMIGANT; FUMIGANTES; MEDICION; MESURE; OZONE; OZONO; PAILLAGE; PHYTOTOXICITE; POLLUTION ATMOSPHERIQUE; POLUCION DEL AIRE; PROPIEDADES FISICO-QUIMICAS; PROPRIETE PHYSICOCHIMIQUE; PROTECCION AMBIENTAL; PROTECTION DE L'ENVIRONNEMENT; SOL; SORCION DEL SUELO; SORPTION DU SOL; SUELO

Methyl bromide is a broad spectrum soil fumigant with a very low boiling point and a very high vapour pressure. The application doses and modes are strictly regulated and necessitate especially trained people for reasons of toxicity hazards. This compound is adsorbed on the soil aqueous phase. It is subsequently converted giving rise to inorganic bromides. These bromides are easily absorbed by crops occasionnally leading to exceeded bromide residues with regard to the established maximum residue levels. In view of reduced input of methyl bromide into soil with subsequent lower toxicity and bromide residue hazard, two nearly unexplored possibilities were studied, i.e.: the use of non-pesticidal admixed compounds that enhance methyl bromide methyl in soil, and the use of improved gastight plastic film soil mulches. The combination of both possibilities was also studied. Admixing co-fumigants, at about equal doses of the reduced methyl bromide dose, showed a longer persistence of freely diffusing methyl bromide in the soil gas phase and a slower generation of soil bromide residues. Co-fumigant requirements of gas density and volatility lead to also halogenated compounds. It was demonstrated that former losses of almost 80 per cent of the applied methyl bromide through the plastic mulch could be reduced considerably using newly developed co-extruded multilayer films. Theoretically, i.e. without losses borders and around greenhouse posts, 20 per cent of the original dose should be sufficient to achieve soil borne disease and pest control. At the end of the long experimental period, methyl bromide became a suspected stratospheric ozone depletor under the extended Montreal Protocol. Being aware that this compound is actually irreplaceable for different kinds of disinfectating goals, the experimental results clearly point to the practical possibilities of the most obvious measure, i.e. to reduce methyl bromide emission to the atmosphere. Although the importance of anthropogenic methyl bromide impact on the cited ozone depletion is not proven, some halogenated candidate co-fumigants are prohibited by the same protocol. Non-halogenated compounds were ultimately tested within that respect.