Monitoring herbicide residues in springflow after an operational application of hexazinone.

Parts of two forested watersheds (440 ac and 482 ac) in central Tennessee were aerially treated with 15 pounds per acre of hexazinone pellets (10 percent active ingredient) to remove hardwood competition prior to establishing loblolly pine (Pinus taeda L.). Both treated watersheds and a control were monitored to determine if hexazinone residues were entering ground water and appearing in springflow. Seven months of monitoring included two intensively sampled periods during application and the first storm. No detectable residues of hexazinone or its two primary metabolites were measured in samples from a watershed in which hexazinone was applied up to 66 feet from the monitoring point. Springflow samples from a watershed treated a year earlier were also clear of herbicide residues.