Integrated analysis of weed control practices for reducing atrazine contamination in an agricultural watershed

Abstract

Atrazine has been detected in more than 90% of raw drinking water samples in northern Missouri, including the Route J watershed, and half of those samples had atrazine concentrations that exceeded the drinking water standard of three parts per billion. An integrated bioeconomic-weed management model was used to evaluate the effects on water quality and profitability of 46 preplant and preemergence herbicide treatments, 67 postemergence herbicide treatments, and 260 two-pass herbicide treatments for weed control in corn production in the watershed. The percentage of total treatments that were profitable was the highest with postemergence treatment (38%), the second highest with preemergence treatment (36%), and the lowest with two-pass treatment (27%). The latter only allows postemergence application of atrazine. Of the nine weed population scenarios evaluated, atrazine was used in 15% to 28% of the profitable two-pass treatments, 27% to 38% of the profitable postemergence treatments, and 81% to 100% of the profitable preemergence treatments. Using average rainfall, a simulation model indicated that the atrazine concentration in surface runoff in the watershed generally exceeded three parts per billion for the profitable preemergence treatments, and was less than three parts per billion for the profitable postemergence and two-pass treatments. Two-pass treatment offers farmers in the watershed additional flexibility in maintaining the profitability of corn production while reducing the atrazine contamination of surface runoff.