SORPTION AND DEGRADATION OF SELECTED FUNGICIDES IN THE TURFGRASS CANOPY

摘要

Microbial degradation of fungicides on leaf surfaces after repeated applications to turf-grass was investigated. Prior and current work in our laboratory has identified two characteristics of the turfgrass leaf system that may contribute to the enhanced degradation of fungicides after repeated application to turfgrass: (1) The leaf surface is rich in microorganisms (～10~8 g~(-1) dr wt leaf), and (2) Leaf surface microorganisms may respond to repeated fungicide applications in a manner consistent with the phenomena of enhanced biodegradation. Field studies were conducted on 'Penncross' creeping bentgrass with four fungicides representing three chemical families applied either two or eight times in one growing season. Biodegradation was estimated using data from both a field study and a parallel laboratory study that followed the fate of ~(14)C-labelled fungicides. For the laboratory incubations, the locations of the residual ~(14)C fungicides were estimated using a sequential extraction protocol that fractionated the materials into three pools: available, retained and bound. Data from both the field and laboratory study refuted our hypothesis that enhanced biodegradation would develop following repeated applications of the fungicides onto the leaf surface. Our studies support a conclusion that a two-stage physical sorption process leads to plant incorporation and this controls most of the fungicide's fate. Thus, our data suggest that microbial activity plays a less important part in the process than would be indicated by considering the size of the microbial population on the leaves.