Irrigation is not Critical to Herbicide Efficacy

Researchers at the US Department of Agriculture's Agricultural Research Service (USDA-ARS) and the Colorado State University found that crop and herbicide use history are more critical to herbicide efficacy and environmental safety than the timing and amount of irrigation water used. Reporting in the Journal of Environmental Quality, Dale Shaner and Lori Wiles said the rate of degradation of atrazine by soil microbes in the top foot of soil is not influenced by the amount, or even the absence, of irrigation. The only factors that made a difference were prior herbicide use and the choice of crop sequences, with prior herbicide use the most important factor by far. Earlier applications of atrazine can predispose soils to more quickly degrade applications of herbicide.

Rapid dissipation of atrazine in the plots can cause a loss in weed control. In the plots with the most rapid dissipation, weeds began to re-infest the plots within four weeks after treatment, while the plots with the slowest rate of dissipation remained weed-free through the growing season. The herbicide leached more deeply in the soil in the plots where it did not dissipate rapidly, but atrazine did not move below the top three inches of the soil in the plots where it was degraded rapidly.

The original story is available at http://www.ars.usda.gov/is/pr/2010/100317.htm