Herbicides in the Pecatonica and Yahara Rivers in Southwestern Wisconsin, May 1996-July 1996

Abstract

Herbicides, particularly those applied to corn, can be found in surface water and ground water in Wisconsin (Sullivan and Richards, 1996; Matzen and Saad, 1996). Wisconsin farmers applied 7.6 million pounds of corn herbicides during 1996. Because of public concern about the amount of herbicides applied to Wisconsin farm fields and the impact on surrounding watersheds, a study was conducted to measure herbicide runoff in sections of two rivers in southwestern Wisconsin. This is a cooperative project between the U.S. Geological Survey (USGS) and the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP). Prior to this study, surface-water samples had not been collected frequently enough to calculate herbicide loads for entire watersheds in southwestern and south-central Wisconsin. This fact sheet summarizes herbicide concentrations in samples collected from the Pecatonica River at Martintown and the Yahara River near Fulton from May 15 to July 15, 1996. Herbicide loads and unit area loads are calculated for these two watersheds. This study monitored commonly applied corn herbicides: alachlor, atrazine, metolachlor, cyanazine, and acetochlor. Acetochlor was introduced to the market in 1994 as a replacement for corn herbicides such as alachlor.