PENDIMETHALIN VOLATILITY FOLLOWING APPLICATION TO TURFGRASS

Volatilization can be a significant avenue of loss for some pesticides following application to field crops or soil. Volatility following pesticide application to dense turfgrass, however, has not been well documented. This work characterized volatilization of the preemergence herbicide pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] following application to a Kentucky bluegrass (Poa pratensis L.) turf. Pendimethalin [60% water dispersible granules (WDG)] was applied at 3.4 kg ha-1 with volatilization losses monitored over a period of 15 d. Pendimethalin vapor flux followed a diurnal pattern with maximum daily flux usually occurring 1300 to 1500 h. Maximum flux of airborne residues occurred 1300 to 1500 h. Maximum flux of airborne residues occurred 1300 to 1500 h on the day of application when losses totaled 23.6 g ha-1 h-1. Pendimethalin volatile losses were 4.8% (165 g ha-1) of the original application during the first 24 h following application. Overnight (1900 to 0700 h) volatile losses measured 9.5 and 10.5 g ha-1 on Days 1 and 2 of the experiment (each overnight loss approximately 0.3% of application). Volatile losses during the 48 h following application totaled 6.1%, with an estimated loss of approximately 13% during the 5-d period following application. Daily volatile loss declined in a diphasic manner over the course of the study, with an initial period of rapid decline in daily vapor flux lasting 5 to 7 d followed by a period of slower decline for the remainder of the study. Dissipation of foliar dislodgeable residues followed a diphasic decline similar to that observed for daily airborne loss, suggesting a relationship between pendimethalin volatilization and foliar dislodgeable residues over time.