Fate of simazine in a drip-irrigated Vitis vinifera vineyard

To determine simazine movement and dissipation in a drip-irrigated vitis vi nifera vineyard under two irrigation schedules [grower standard (GS) and cu rrent evaporation/transpiration (CET)], field experiments were conducted in a Hanford fine sandy loam, a soil type prone to leaching. In experiment 1, simazine was surface-applied in a 1.7-m swath down the vine row and chlori de was applied as a tracer. Total recovery of simazine was < 1.0% under the irrigation emitters 51 and 57 d after simazine application in 1997 and 199 9, respectively. Simazine was not detected in the soil profile from 0 to 15 0 cm deep, 1.0 m from the emitters. A chloride tracer moved to a soil depth of 90 cm but not deeper. In experiment 2, simazine moved 75 cm under the e mitters in 7 d but did not. move deeper into the soil. Under the emitter, 2 8% of applied simazine was found 0 to 45 cm deep and 3% was > 45 un deep. I n experiment 3, which was conducted in the absence of irrigation. total rec overy of simazine was 30% when sheltered from rain and 8% when exposed to r ain. Rapid dissipation and proper irrigation management were key factors pr eventing deep percolation of simazine in these studies.