Atrazine is a widely used soil-applied herbicide to control many broadleaf and grassy weeds in corn, sugarcane, and non-cropland areas.  Atrazine is also found as a contaminant in surface and ground water.  One of the strengths and weaknesses of atrazine has been the long residual activity in the soil that provides good weed control but also increases the leaching of the herbicide.  In the last 5 years my research has focused on the phenomenon of enhanced atrazine degradation in soils that have received multiple applications.  Enhanced atrazine degradation is due to the selection of soil microbes that have the ability to metabolize atrazine as a source of nitrogen.   I have conducted surveys in collaboration with other scientists throughout the U.S. on the extent of enhanced atrazine degradation in multiple cropping systems including corn, sugarcane, and vineyards.  In all cases where atrazine has been extensively used, we find enhanced degradation.  The primary factors that correlate with atrazine degradation are years of use and soil pH.  Enhanced atrazine degradation leads to a loss of long-term residual weed control, but also decreased leaching and persistence in the environment.