Pendimethalin Dissipation in Kentucky Bluegrass Turf

Pendimethalin dissipation was studied following annual 1.7 kg ai ha–1 applications to 3-yr-old Kentucky bluegrass turf growing on a Sharpsburg silty clay loam soil and an 85/15 by volume sand/Sharpsburg soil mixture in 150-cm-deep rhizotron containers. Plant tissue, thatch, and soil were sampled periodically between application and 168 days after treatment (DAT). Soil and leachate were collected to monitor pendimethalin movement. Most of the herbicide appeared to remain within the turfgrass system. Pendimethalin concentration was highest in plant tissue and thatch. The 4-hydroxymethyl pendimethalin metabolite was detected in turfgrass tissue up to 42 DAT. No pendimethalin was detected at the 30-, 60-, or 120-cm depths in the rhizotron containers. Traces (≤0.003 mg kg–1) of pendimethalin detected in rhizotron leachate collected between 6 and 14 days after heavy rainfall (88 and 95 DAT, respectively) were attributed to gravitational displacement of soil colloids containing adsorbed herbicide. Pendimethalin application to established turfgrass would not appear to pose a high risk of groundwater contamination.