Effect of turfgrass on soil mobility and dissipation of cyproconazole

Previous studies of pesticide fate in turfgrass have found less mobility an d more rapid dissipation compared with studies using the same pesticide app lied to bare soil. Few direct comparisons of pesticide mobility and dissipa tion in turfgrass vs, bare soil have been conducted. The mobility and persi stence of cyproconazole [alpha-(4-chlorophenyl)-alpha-(1-cyclopropylethyl)- 1H-1,2,4-triazole-1-ethanol] on bare soil (Flanagan silt loam; fine, smecti tic, mesic Aquertic, Argiudoll) and turf containing varying levels of organ ic matter was examined under field conditions. Twenty-centimeter-diameter p olyvinyl chloride (PVC) cylinders were installed in either creeping bentgra ss turf (Agrostis palustris Huds.), or in turf in where either 33, 67, or 1 00% of the thatch and plant material had been removed. Cyproconazole was ap plied at 403 g a.i, ha(-1) on 15 July 1996 and 8 July 1997. Replicate sampl ing 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 cyp roconazole in the 0- to 1-, 1- to 3-, 3- to 5-, and 5- to 15-cm core sectio ns. 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 mo vement below 5 cm in the soil was reduced with increasing amounts of turfgr ass thatch, and as little as one-third of a full stand of turf greatly decr eased the half-life of cyproconazole. Application of cyproconazole to turfg rass results in less mobility and more rapid dissipation than is typically reported in other agronomic crops.