Articles
DISTRIBUTION PATTERNS AND NEMATOCIDAL ACTIVITY OF METHYL BROMIDE IN VARIOUS SOIL CONDITIONS AND METHODS OF APPLICATION
With eggs and larvae of Meloidogyne arenaria, the C x T product appears to be a good physical measure of bioactivity.
However, bioactivity also depends on several edaphic factors such as soil temperature and moisture content.
Under normal conditions of surface application under polyethylene sheet, the vertical distribution of M.B. is rather ensured by gas initial decompression than by molecular diffusion in soil air.
But on a consequence of polyethylene permeability of M.B., deep penetration is limited and a large part of the applied pesticide escapes into the atmosphere.
Among the edaphic parameters affecting M.B. distribution, the most important one is soil organic matter content.
Adsorption reduces the concentration of available pesticide and adsorbed molecules lose their bioactivity.
Nevertheless, at usual dosage (75 g/m2), the C x T product in the first 60 cm of soil is much higher than the lethal value.
The above considerations emphasize the necessity of improving methods of application in order to avoid losses of M.B. and to adjust doses in real soil conditions.
In our experiments we obtained good nematocidal activity in the upper 60 cm by insuflating mixtures of air and M.B. at very low dosage (10 to 20 g/m2) in soil under a "Saran" cover.