Downward Mobility of Select Herbicides In a Bermudagrass Fairway Versus Fallow Bare Ground.

Pesticide regulations for turfgrass may be based on row crop agriculture environmental fate data.  Previous research has demonstrated this may not be accurate as select pesticides have been documented to behave differently in bare ground compared to established turfgrass.  Research was conducted to compare downward mobility of select herbicides in fallow bare ground compared to an established turfgrass system.  Applications to actively growing bermudagrass versus dormant turf were also compared.  Evaluated herbicides included atrazine, mesotrione, MSMA, pendimethalin, and sulfentrazone.  Field lysimeters comprised of 90% sand were utilized and irrigated immediately after application to simulate a worst-case scenario.  Lysimeters were exhumed 120 days after initiation and divided into respective depth increments.  Parent pesticide residue levels were determined for each soil depth utilizing published extraction and analysis methodology.  Greater downward mobility occurred in fallow bare ground compared to established turfgrass systems indicating leaching potential of evaluated herbicides is greater in fallow bare ground compared to established turfgrass systems.  Regardless of system, minimal atrazine was recovered after summer applications while twice the amount of atrazine was recovered in turfgrass compared to a fallow bare ground system after winter applications.  Of recovered atrazine, 90% was recovered within four cm of soil surface in turfgrass whereas only 60% was recovered in same depth increment in fallow bare ground system.  When sulfentrazone was applied to dormant bermudagrass, 78% more was recovered compared to a fallow bare ground system.  Additionally, 45% greater was recovered within four cm of soil surface in turfgrass compared to fallow bare ground applied during summer.  These data indicate downward mobility of select herbicides vary when applied to established turfgrass compared to fallow bare ground systems likely due in part to increased organic matter as well as greater, more diverse microbial populations in established turfgrass systems.