Articles
AN EVALUATION OF THE SOIL DISINFESTATION PRACTICES IN BELGIUM AND PROBLEMS INVOLVED WITH EFFICIENCY, SAFETY AND IMPACT ON THE ENVIRONMENT
About 80 % of the total greenhouse area, used for vegetable production, is fumigated with methyl bromide.
This has a phytotechnical as well as an economical basis.
A short waiting period is combined with a very good penetration and spread of the compound, resulting in, generally, very good disease control.
Till 1979 the mixture of methyl bromide with chloropicrin was used, especially in the summer period.
This mixture with synergistic activity was used to increase the efficiency against certain fungi (Pyrenochaeta lycopersici, Phomopsis sclerotioides) and to decrease the methyl bromide dose (Bromine residues). For safety reasons, the application of this product by means of injection equipment in greenhouses was not longer allowed.
From that time methyl bromide is applied in glasshouses only by means of surface application of heated gas.
Because of the very high gas concentrations that can occur inside the glasshouse, the use of authonomous gas masks was prescribed.
With this method of methyl bromide application efficiency can be problematic at the borders of the greenhouse, especially in winter time or when no special precautions were taken to prevent gas escape.
Also the risk for irregular spread of the gas exist.
To prevent the accumulation of bromide residues in edible plant parts, higher than the fixed tolerances, special precautions are to be taken.
One of them is leaching the soil after fumigation and aeration with high amounts of water (250–500 1/m2). Because most residue problems were stated with lettuce immediately after MB treatment, the allowed general dose (9 kg/are) was decreased (till 5 kg/are) before leafy crops as lettuce and spinach.
This resulted in a partial changement of disinfestation practices, e.g. fumigation before the tomato crop in winter time, in stead of before the lettuce crop in summer time.
Leaching during winter time is less efficient and problems with Bromine residue in tomatoes can occur.
By leaching the soil Bromine is evacuated via the drainage system to the surface water.
Water analysis in Belgium and Holland show the enormous difference in concentrations between the two entirely different regions.
Data about methyl bromide concentrations in the drainage and surface water during leaching the greenhouse, as well as about the air pollution during fumigation exist only on a limited scale for our situations, however, an extended measuring program will be carried out in the near future by the Institute of Chemical Research of Tervuren, on which we will cooperate.