Influence of Formulation and Irrigation Incorporation on Offsite Movement of Atrazine from Centipedegrass.

Atrazine, one of the most widely used herbicides in the United States, is commonly applied to southern lawn grasses to reduce weed encroachment.  According to the EPA, atrazine is also one of the most frequently identified herbicidal compounds in surface and ground waters.  The combination of increased management intensity of home lawns and high rainfall in Louisiana increases the potential for movement of atrazine into surface waters during runoff events. Therefore, experiments were conducted to evaluate the effect atrazine formulation and post application management have on atrazine movement in centipedegrass [Eremochloa ophiuroides (Munro) Hack]. Treatment combination included atrazine applied as a granular or liquid and incorporated with 2.5 cm of irrigation or not incorporated.  Three days post-atrazine application, treatment combinations were subjected to rainfall simulation for 30 min surface runoff.  Time until runoff, total solids lost, and runoff volume were measured.  Runoff waters were sampled every 5 min for 30 min and analyzed for atrazine.  Rainfall simulations were also performed 15 and 30 days post-atrazine application with 30-min composite runoff samples analyzed.  A second experiment was conducted to compare runoff losses of atrazine versus simazine, a less water soluble herbicide that targets similar weed species.  Runoff of granular and liquid applied atrazine differed across the observation period with incorporation of atrazine reducing atrazine losses.  Choosing simazine rather than atrazine also reduced offsite movement.  The goal of this research is to development best management practices regarding atrazine application for homelawns in Louisiana.