Pesticide Residue Laboratory, Indian Institute of Horticultural Research, Hessaraghatta, Bangalore, 560 089
The buildup of the residues and their dissipation pattern of the four promising synthetic pyrethroids viz. permethrin, fenvalerate, cypermethrin and dehamethrin on cabbage heads was studied at their effective application rates under supervised field trials. The periodic analysis of residues was done by gas liquid chromatography. Pyrethroid lesidues were found dissipating at the half life values of 2.6 to 2.9 days for permethrin; 2.7 to 2.8 days for fenvalerate, 1.9 to 2.5 days for cypermethrin and 1.6 to 3.0 days for dehamethrin respectively. The persistence pattern of their residues therefore warrant observing the waiting periods of 11 to 13 days for permethrin, 11 to 14 days for fenvalerate, 6 to 9 days for cypermethrin and 2 to 4 days for delta-methrin depending on their recommended maximum permissible levels.
