Weed control and herbicide residues in onion following use of chlorpropham and cyanazine

Abstract

AbstractA gas chromatographic method, using nitrogen‐phosphorus alkali flame ionization detection, is presented for the determination of residues of chlor‐propham and cyanazine in onion (Allium cepa L.). Recoveries of chlorpropham and cyanazine were 94 (±16)% and 84 (±7)% at the 100μg kg‐1 fortification level, and 97 (±8)% and 88 (±10)%, respectively, at 50μg kg‐1. Analysis of immature (whole plants) and mature (bulbs only) onions grown at four sites following a pre‐emergence application of chlorpropham at 6.0–6.7 kg ha‐1 and a subsequent post‐emergence application of a tank mixture of chlorpropham plus cyanazine at 4.5 and 1.1 kg ha‐1, respectively, resulted in no detectable residues of either herbicide. Weed control efficacy was evaluated for two consecutive years. The treatment demonstrated 88 % and 70 % broad‐leaved weed control 13 and 27 days after application, respectively, at the one site in Quebec.