Phytotoxicity of Trifluralin Vapors from Soil

Abstract

Foxtail millet [Setaria italica(L.) Beauv. ‘Empire’] and proso millet(Panicum miliaceumL. ‘White’) seedlings were grown in glass units to expose selectively either roots or shoots to vapors arising from soil containinga,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). The root and shoot growth of both species was inhibited by trifluralin vapors. Suppression of root and shoot growth increased as trifluralin application rates increased. In shoot exposure, vapors arising from soil treated with 5 ppmw of trifluralin were lethal to seedlings of both species. In root exposure, root growth of both species was severely suppressed at 20 ppmw, but shoot growth was unaffected. Phytotoxic effects resulting from a given concentration of trifluralin were more severe as greater carrier volumes were used for application. Trifluralin vapors arising from soil 16 to 22 days after treatment were still sufficient to cause shoot growth inhibition.