Simazine Residue Levels in Irrigation Water after Ditchbank Application for Weed Control 1

A field study was conducted to determine the amount of simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] likely to be found in irrigation water after ditchbank treatment for weed control. Resulting data are useful in evaluating the potential impact of simazine on crops irrigated from sprayed canals. Canals were selected in California, Colorado, and Washington for the application of simazine to both watered and dewatered sites at rates of 2.25 to 7.43 kg/ha. Simazine levels in flowing canal water immediately after herbicide application did not exceed 60 µg/liter. In first-flow samples collected in the spring from the sites that were dewatered at application, simazine levels peaked at about 250 µg/liter within the treated section but decreased rapidly to <5 µg/liter.