Behaviour of fenitrothion residues in leaves and soil of vineyard after treatment with microencapsulate and emulsified formulations

Abstract

The rate of decline of fenitrothion residues was investigated in leaves and soil of vineyard over 2 months after treatment with two different kinds of commercial formulations: emulsifiable concentrate (EC) and microencapsulate (ME). Fenitrothion residues were determined with GC-NPD after acetone extraction of soil and leaves. The measured initial deposits in soil and leaves varied between 2.6 and 3.8 mg kg−1 and between 89 and 101 mg kg−1, respectively. Fenitrothion residues in soil dropped at 0.1–0.2 mg kg−1 after 60 days following application with EC formulation showing a more rapid decline than the ME. Fenitrothion residues in leaves from ME formulation treatment showed a longer persistence and lower decline rate than those from EC formulation. During the experimental period, fenitrothion remaining in leaves from ME application was 10 times more than from the EC one. Mathematically defined decline curves were established by determining optimal relationships between fenitrothion residues and time. The RF1st-order and RF1.5th-order equation achieved the best adjustment to the experimental data of fenitrothion dissipation on leaves for the ME and EC formulation, respectively, giving fenitrothion half-lives of about 2–3 days for ME and <1 day for EC formulation. In vineyard soil, the best adjustment to the experimental data for ME and EC formulation was achieved by the 1st-order and 1.5th-order equations, respectively, giving fenitrothion half-lives in soil of about 17–21 days for ME and 5 days for EC formulation.