Effect of turfgrass on soil mobility and dissipation of cyproconazole

Previous studies of pesticide fate in turfgrass have found less mobility and more rapid dissipation compared with studies using the same pesticide applied to bare soil. Few direct comparisons of pesticide mobility and dissipation in turfgrass vs, bare soil have been conducted. The mobility and persistence of cyproconazole [alpha-(4-chlorophenyl)-alpha-(1-cyclopropylethyl)-1H-1,2,4-triazole-1-ethanol] on bare soil (Flanagan silt loam; fine, smectitic, mesic Aquertic, Argiudoll) and turf containing varying levels of organic matter was examined under field conditions. Twenty-centimeter-diameter polyvinyl chloride (PVC) cylinders were installed in either creeping bentgrass turf (Agrostis palustris Huds.), or in turf in where either 33, 67, or 100% of the thatch and plant material had been removed. Cyproconazole was applied at 403 g a.i, ha(-1) on 15 July 1996 and 8 July 1997. Replicate sampling cylinders were removed 2 h after treatment (HAT) and 4, 8, 16, 32, 64, and 128 d after treatment (DAT), Cylinder cores were sectioned into depths and assayed for cyproconazole by gas chromatography. On all sampling days, increasing the amount of surface organic matter decreased the amount of cyproconazole in the 0- to 1-, 1- to 3-, 3- to 5-, and 5- to 15-cm core sections. The amount of cyproconazole detected in the soil under a full stand of turf at 4 and 32 DAT was 1 and 11%, respectively, of that detected in bare soil. Cyproconazole residues never exceeded 20 mu g kg(-1) in the 15- to 30-cm core section of any treatment. The half-life of cyproconazole decreased from 129 d in bare soil to 12 d in a full bentgrass turf. Cyproconazole movement below 5 cm in the soil was reduced with increasing amounts of turfgrass thatch, and as little as one-third of a full stand of turf greatly decreased the half-life of cyproconazole. Application of cyproconazole to turfgrass results in less mobility and more rapid dissipation than is typically reported in other agronomic crops.