Twenty Years of University Corn Yield Data: with and without Atrazine

Herbicide efficacy studies reporting corn yields published in the North Central Weed Science Society Research Report were analyzed to calculate average corn yields for treatments either containing atrazine or not containing atrazine. To prevent unequal comparisons, studies and treatments had to meet conservative selection criteria in order to be included in the analysis. Treatments had to control both broadleaf and grass weeds (normally containing at least two active ingredients), and active ingredients had to be currently registered for use and used at label rates. For the 20-year period, 19862005, 236 qualifying studies were identified, with a total of 5,871 qualifying treatments. For the period 1986-1995, corn yielded an average 6.3 bushels/acre higher or 5.9% higher with atrazine than without. For the period 1996-2005, corn yielded an average 5.4 bushels/acre higher or 4.6% higher with atrazine. For the entire 20-year period, the average yield with atrazine was 5.7 bushels/acre higher or 5.1% higher with atrazine than without. Corn yields with atrazine continued to be higher than with non-atrazine treatments as new active ingredients and new technologies such as herbicidetolerant corn hybrids were introduced. University researchers have increasingly added atrazine to new active ingredients to improve weed control. In 1986, 55% of all evaluated treatments in studies contained atrazine. As many new active ingredients were evaluated, treatments containing atrazine dropped to 17% in 1995. However, by 2005, 79% of all treatments in the studies evaluated contained atrazine. Considering the value of increased corn yields with atrazine and the lower cost of atrazine compared to alternatives, atrazine use added an estimated $25.74 per acre income to farmers in 2005, with a total U.S. benefit to farmers of $1.39 billion.