Fate of trifluralin and triallate applied as a mixture to a wheat field
Grover, R. | Smith, AE. | Shewchuk, S.R. | Cessna, A.J. | Hunter, J.H.
Dissipation of triallate [S-(2,3,3-trichloroallyl) diisopropyl-thiocarbamate] and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) in air and soil was?measured following their application as a pre-emergence treatment to a wheat (Triticum aestivum L.) field. Drift losses during application and incorporation were less than 1% of the amounts applied. Air samples, collected at six heights ranging from 30 to 200 cm above the soil surface initially and then shove the crop canopy following emergence during the 67 d after application, showed distinct gradients of each herbicide in the air, with the highest concentrations in samples closest to the ground. The highest flux rates for triallate and trifluralin were 4 and 3 g ha-1 h-1 during the 4- to 6-h period after application, when the concentrations at 30 cm were 2500 and 1700 ng m-3 respectively. Fluxes of both herbicides decreased with lime, but were dependent mainly on soil moisture conditions. The total vapor losses for the 67-d sampling period were 17.6 and 23.7% triallate and trifluralin, respectively. About half of these losses were in the first week. There were three distinct phases in the dissipation of both herbicides from the soil. The initial rapid phase, with vapor losses as the major route (Phase I), was followed by slow and continual dissipation over the entire growing season (Phase II), with volatilization and degradation as the potential pathways of dissipation. The third phase with little or no dissipation was reflective of the Canadian winter conditions. The gross dissipation of both herbicides during Phases I and II, however, followed the first-order rate equation, with half-concentration time of 88 +/- 7 and 99 +/- 9 d for triallate and trifluralin, respectively, with volatilization as the dominant process during Phase I.
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