Persistence of fenamiphos plus its metabolites in Moroccan soil under banana cultivation.

Persistence of fenamiphos (ethyl 4-methylthio-m-tolylisopropylphosphoramida te) was studied after three consecutive treatments in a field trial in a ba nana plantation over one growing season (1993). The total residue of fenami phos (TR) plus its metabolites showed a rapid initial decline in the upper layer of the soil (0-10cm) after the first and the second treatment, follow ed by a slow disappearance. The end of the rapid phase coincides with the a ppearance of fenamiphos and its metabolites sulfoxide and sulfone mainly in the lower layer of the soil (10-30cm). The three compounds tend to disappe ar there after. After the third treatment, the trend was similar for fenami phos and its metabolites. However, higher residue levels were detected in t he two layers of the soil, due probably to reduced leaching under the low i rrigation regime applied. Experimental half-lives ranged between 4-16 days. Residue data gave a good fit to the second-order kinetic model.