|Hansen, Neil - COLORADO STATE UNIVERSITY|
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 13, 2007
Publication Date: February 5, 2008
Citation: Shaner, D.L., Wiles, L., Hansen, N. 2008. The Effect Of Cropping And Herbicide Use History On Atrazine Efficacy And Dissipation. Weed Science Society of America Meeting Abstracts: Poster presentation at the WSSA Annual Meeting in Chicago, IL Feb. 5, 2008 Technical Abstract: Previous research has shown that atrazine dissipates rapidly in fields in Colorado where the herbicide has been used continuously for 3 or more years. A small plot study with four replications was done in two locations in 2007 as part of a larger project on irrigation water optimization. Three cropping patterns were examined: (1) Corn-Alfalfa Rotation (4 y corn followed by 4y alfalfa)-conventional tillage; (2) Corn-Alfalfa Rotation (4 y corn followed by 4y alfalfa)-conservation tillage and (3) Sunflower-Wheat-Corn Rotation-conservation tillage, limited irrigation. In (1) and (2), the plots were in the third year of corn and the plots had been treated with 1.68 kg/ha atrazine the previous two years. In (3) the corn was planted into wheat stubble, and the plots had received no atrazine in the previous two years. The plots in (1) and (2) were treated with 1.68 kg atrazine /ha and (3) with 1.12 kg atrazine /ha in May, 2007. Four 1.9 cm X 30 cm soil cores were removed from each plot at 5, 12, 19, 26, 33, 47, and 62 d after treatment (DAT). The columns were divided into 7.5 cm increments and each increment combined. Atrazine was extracted from each soil sample and quantified on a GC/MS. In addition, the rate of dissipation of atrazine in the soil from the top 7.5 cm was tested in a laboratory assay. There was a significant difference in the rate of atrazine dissipation among the treatments in the laboratory study. The half life (T 1/2) of atrazine in the soil from the continuous corn plots was less than 1d, whereas it was between 3 and 5 d in soil from the corn following wheat plots. The T 1/2 of atrazine in the field plots was also much shorter in (1) and (2) (1.6 to 8 d) compared to (3)half life(16.8 to 24 d). Control of barn yard grass, pigweeds, and foxtails was poor in the plots where the atrazine dissipated rapidly. At 42 DAT, weed seedling density in (1) and (2) was up to 206 and 186 plants/m of row, respectively, whereas it was a maximum of 2 plants/m of row in (3) even though (1) and (2) had received 50% more atrazine compared to (3). These results indicate that the enhanced degradation of atrazine can occur within 3 years of continuous application and the enhanced degradation results in a loss of residual weed control.