Comparative Persistence of Dinitroaniline Type Herbicides on the Soil Surface

Field and laboratory experiments were conducted over a 3-yr period to evaluate the persistence of several dinitroaniline herbicides. Incorporation of these herbicides was delayed for 1, 3, and 7 days after application. Herbicidal activity was assessed by a sorghum bioassay, and by GLC analysis of soil samples. Herbicides least affected by a 2-day delay in incorporation were oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide, nitralin 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline, butralin 4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralinN-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline, and penoxalinN-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine. Of the herbicides evaluated, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-P-toluidine) and profluralinN-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine, were the least persistent after a 1-day incorporation delay. Losses of nitralin, butralin, dinitramine, fluchloralin, penoxalin, trifluralin, profluralin, benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), and isopropalin (2,6-dinitro-N, N-dipropylcumidine) increased dramatically when incorporation was delayed 3 or more days. Persistence on the soil fur-face under field conditions was demonstrated the most by oryzalin. After incorporation, dinitramine was least persistent. The effects of temperature in UV light and dark on loss of dinitroaniline herbicides were demonstrated in the laboratory by applying the herbicide to TLC plates of soil. While herbicide losses did occur in 24 h of UV light, differences in herbicide losses were not significantly different between butralin, penoxalin, profluralin, trifluralin, isopropalin, oryzalin, nitralin, fluchloralin, and benefin. Dinitramine was most affected by the UV light. Butralin, oryzalin, nitralin, isopropalin, and dinitramine were least affected by 45 C in the dark with losses of 2 to 10% in 24 h. Profluralin, benefin, and trifluralin were found most volatile with losses of 35%, 25%, and 18%, in 24 h respectively. With increasing moisture levels, no significant increased losses were detected for butralin, nitralin, oryzalin, penoxalin, and isopropalin at the greater moisture contents. There was a moderate increase in the loss of dinitramine with increased soil moisture. AT 33% initial soil moisture, fluchloralin, benefin, and trifluralin were rapidly lost (75 to 94% in 24 h at 30 C). The trifluoro-methyl group was a common structural component where moisture affected the compound's loss. Application of the intermediate to very volatile dinitroanilines to moist soil surfaces without soil incorporation as soon as possible is not feasible unless higher rates of herbicide are applied.