Persistance and phytotoxicity of dinitroaniline herbicides in Manitoba soils

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Pritchard, Mervyn Kenneth
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The persistence and phytotoxicities of trifluralin (a, a, a-trifluro-2, 6-dinitro-N-dipropyl-p-toluidine), profluralin (N-(cyclopropylmethyl) -a, a, a-trifluro-2, 6-dinitro-N-propyl-p-toluidine), fluchloralin (N-(2-chloroethyl)-2, 6-dintro-N-propyl-4-(trifluromethyl) aniline), and dinitramine (N4, N4 -diethyl -a, a, a-trifluro-3, 5-dinitrotoluene-2, 4-diamine) were compared in Manitoba soils. Analytical determinations and field bioassay results, one year after application of the chemicals on light soil, indicated the order of persistence as: profluralin > trifluralin > fluchloralin > dinitramine. On heavy soils, the order of dinitroaniline persistence was: profluralin > dinitramine > trifluralin > fluchloralin, one year after application of the chemicals. Organic matter increased persistence of trifluralin and fluchloralin while clay content increased persistence of profluralin and dinitramine. The phytotoxicities of dinitroanilines were: dinitramine > trifluralin > profluralin = fluchloralin. They phytotoxicites of all chemicals decreased with increased organic matter. Under low soil temperatures (4oC), trifluralin caused a greater inhibition of wild oat (Avena fatua L.) roots than the other chemicals while dinitramine and fluchloralin were the most phytotoxic herbicides at the higher temperatures (8oC). Root length was the best criterion for detection of dinitroaniline herbicide activity. Shoot growth was inhibited most by trifluralin at all temperatures tested but shoot dry weight was a poor indicator of herbicide injury.