A Field Study of the Fates of Arsenal and Escort Applied on the Cumberland Plateau in Tennessee

Problem statement: The low organic soils of the Cumberland Plateau, as well as the karst geology of the region, may promote increased transport of herbicides outside of application sites. We have studied the fates of imazapyr and metsulfuron-methyl applied to a privately owned tract on the Cumberland Plateau in Tennessee and compared the field results with herbicide fate predicted by the computer model GLEAMS. Approach: The fate of the two herbicides, applied for pine release at a site on the Cumberland Plateau, was monitored over a sixteen month period. Concentrations in soil water were monitored using vacuum soil lysimeters. Grab samples were taken of water in ephemeral streams draining the clearcut area and of a perennial stream which receives water from the study area. Uncut streamside management zones of about 50 m bordered the streams. The field results were compared with those obtained using the GLEAMS computer model. Results: Concentrations of both herbicides in soil water dropped significantly within the first two months after application, imazapyr to less than 50 µg L^-1 and metsulfuron-methyl to less than 3 µg L^-1 and decreased more gradually in the following months. The maximum concentrations observed in soil water were 252 µg L^-1 (imazapyr) and 13 µg L^-1 (metsulfuron-methyl). Except on two dates occurring 5 months after application, the herbicides were not detected in the stream samples. GLEAMS predicted that very little herbicide should have been lost from the site in runoff or erosion sediment. The model predicted greater retention of the herbicides by the soil than was found through the field measurements. Conclusion/Recommendation: The rapid transport of imazapyr and metsulfuron we observed indicates that further study is justified at other locations on the Cumberland Plateau. Streamside management zones effectively prohibited contamination of receiving streams by herbicides at the study site.