Effect of turfgrass on soil mobility and dissipation of several pesticides

The mobility and dissipation of several pesticides applied to turfgrass and bare soil was studied under field conditions. Cyproconazole [α-(4-chlorophenyl)-α-(1-cyclopropylethyl)-1H-1,2,4-triazole-1-ethanol] was applied to bare soil (Flanagan silt loam) and creeping bentgrass (Agrostis palustris Huds.) turf containing varying levels of organic matter at 403 g ai ha–1. Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3- dimethylbenzofuran-5-yl methansulfonate] was applied to bentgrass and bare soil at 840 g ai ha–1. Halofenozide (N-4-chlorobenzoyl- N′-benzoyl-N′ -tert-butylhydrazine) was applied to bentgrass, tall fescue ( Festuca arundinacea Schreb.), and bare soil at 1680 g ai ha –1. Mefanoxam [(R)-2-(2,6-dimethylphenyl)-methoxyacetylamino]-propionic acid methyl ester] and propiconazole (1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1 H-1,2,4-triazole) were applied to bentgrass and bare soil under different irrigation schedules at 770 g ai ha–1 and 1540 g ai ha –1, respectively. Sampling cylinders were installed prior to treatment and then removed two hours after treatment and 4, 8, 16, 32, and 64 days after treatment (DAT) and the cores sectioned into depths. Extracts were assayed by HPLC or gas chromatography yielding pesticide detection limits of 0.01 to 0.04 mg kg–1. Cyproconazole leaching in turfgrass at 4 and 32 DAT was 1% and 11%, respectively, of that in bare soil. The half-life (t_1/2) was 129 days in bare soil and 12 days in bentgrass. Ethofumesate leaching in bentgrass was reduced by at least 95% compared to bare soil and the t_1/2 was 51 days in bare soil and 3 days in bentgrass. Leaching of halofenozide in turfgrass and bare soil were similar 32 and 64 DAT and the t_1/2 exceeded 64 days. The t_1/2 of mefanoxam was 5–6 days in turf and 7–8 days in bare soil and residues were found in the 15–30 cm soil layer at 4, 8, 16, 32, and 64 DAT, regardless of surface organic matter. Little propiconazole leaching was observed and the t_1/2 was 12–15 days in turf and 29 days in bare soil. These studies indicate that chemical properties are important in determining if turfgrass cover or irrigation will affect soil mobility and dissipation of pesticides. Application of moderately mobile or immobile pesticides, such as cyproconazole and ethofumesate, to turfgrass results in less mobility and more rapid dissipation than is typically reported in other agronomic crops.