Dissipation of Phosalone and Diazinon in Fresh and Dried Alfalfa

The objectives of this study were to determine the persistence of phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O, O-diethyl phosphorodithioate) and diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) residues in fresh and baled alfalfa under field conditions. Plots of alfalfa were sprayed with each insecticide. Fresh alfalfa was sampled up to 20 days after treatment, and dried alfalfa was sampled up to 25 weeks after baling. Samples were analyzed for residues using high performance liquid chromatography (HPLC) equipped with a UV detector. The half-lives of diazinon and phosalone in fresh alfalfa were 1.8 and 3.3 days, respectively. In baled alfalfa the half-life of diazinon and phosalone were 2.8 and 16.7 weeks, respectively. No diazinon residues were detected in baled alfalfa, sampled after week 9, although the concentration of phosalone found at week 25 was 5.51 mg/kg.