Wednesday, November 15, 2006 - 8:30 AM
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Dissipation of Foliar Carfentrazone Residues Following Herbicide Application to Turfgrass.

C.V. John1, R.J. Cooper1, and Damian Shea2. (1) North Carolina State Univ., Dept. of Crop Science, Campus Box 7620, Raleigh, NC 27695-7620, (2) North Carolina State Univ., Dept. of Environmental & Molecular Toxicology, 850 Main Campus Drive, Raleigh, NC 27695-7633

Following pesticide application to turfgrass, a major source of potential human exposure to pesticide residues is contact with treated leaf tissue. Pesticide remaining as dislodgeable foliar residues (DFR) following application may be defined as those residues most easily dislodged from the foliar surface and available for dermal transfer. On 20 Oct. 2005, the broadleaf-weed herbicide carfentrazone was applied to tall fescue (Festuca arundinacea Schreb.) mown at 7.5 cm using a Lesco Chemlawn® Gun operating at 138 kPa and providing 0.31g in 40 mL water / m2. DFR were obtained by wiping a 9.3 dm 2 area of pesticide-treated turf with dampened cheesecloth to remove residues. Samples were taken immediately after application and 1, 4, and 8h after treatment (HAT); and at noon 1, 2, 3, 5, 7, 11, and 15 d after treatment (DAT). Carfentrazone DFR averaged 2, 175 ng / m2 immediately after application which was 31% of the total amount applied. One HAT, when the herbicide had dried on the turf, DFR had dissipated to only 6.5% of the total amount applied. By four HAT, DFR had dissipated to 3.1% of the total amount applied, or 225 ng / m2. At eight HAT, DFR had dissipated to 2.5% of the total amount applied. Three DAT no DFR were detected. Over the entire 15 day study, DFR totaled 43 % of carfentrazone initially applied. This work confirms that foliar pesticide residues are most available for human exposure immediately after application and that upon drying on the leaf they pose very little exposure to the casual user of the turfgrass area. Greatest exposure concern lies with those mixing and applying the spray solution since these liquid residues are most dislodgeable.