Persistence and degradation of some insecticides in Darjeeling tea

Abstract

A field trial was conducted during dry and wet seasons to understand the occurrence of residues, persistence, dessipation rate and half life values of six widely used insecticides at recommended doses/dilutions viz. Monocrotophos 36% SL, Malathion 50% EC, Fenvalerate 20% EC, Dimethoate 30% EC, Quinalphos 20% AF and Dicofol 18.5% EC in processed tea. The insecticides were applied as aqueous solutions at the dilution of 1:400 for all insecticides except Fenvalerate which was applied @ 1 : 4000 during dry and wet seasons. The initial deposit (4 hrs) of different insecticides except Fenvalerate were found to be higher in dry season than wet season. No residues of Monocrotophos after 4 hrs of its application was detected. The residue of Malathion, Fenvalerate and Dimethoate on 5th day after application were found below the prescribed maximum residue limit. But in case of Quinalphos it was observed on 7th day after application. The residue of Dicofol on 7th day during wet season (0.03 ppm) was found below the tolerance limit. Dissipation followed a first order reaction in all case and the half life values varied from 0.24 to 2.73 days. This study also indicated that one round of plucking may be discarded in dry season when Quinalphos and Dicofol are applied on the tea bushes of Darjeeling.

Books