To assess the flux of a pre-emergent herbicide from silty clay loam soils of the upper Midwest to nearby surface streams and underlying water table aquifers, in-field, length-of-season monitoring was undertaken in six planted, pattern-tiled fields (three fields with stand pipes and three fields without stand pipes) in the states of Minnesota and Wisconsin. Cooperating growers made applications of the herbicide in May 2015 at its maximum label allowable rate. Prior to application and for 100 consecutive days thereafter, tile flow and on-site rainfall were recorded every fifteen minutes; daily flow-proportional composite tile-drain samples and depth-integrated surface water from adjacent ditches or creeks were collected and analyzed using LC-MS/MS with d6-internal standards. Monitoring found very low level of parent, mainly a major metabolite at levels above its level of quantitation during the growing season. Peak concentrations occurred in tile-drain water that coincided with the first two to three rainfall events at each site; concentration of the metabolite quickly dissipated at each site to fractions of its original concentration, likely due to the short half-life of the parent and its metabolites. The overall concentration of the metabolite in the surface water samples was consistently low, owing to the rapid degradation of the parent as well as streamflow dilution. No meaningful difference was observed between the fields with or without stand pipes.

Fate and transport studies of a pre-emergent herbicide in tiled fields of the upper midwest

254th National Meeting (2017)

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