Field Comparison of Seven Dinitroaniline Herbicides for Alfalfa (Medicago sativa) Seedling Establishment

Abstract

In a 3-yr field study, seven dinitroaniline herbicides controlled all weeds adequately, except for two species. None of them controlled shepherdspurse [Capsella bursa-pastoris (L.) Medic.], and only nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] controlled common ragweed (Ambrosia artemisiifolia L.). EPTC (S-ethyl dipropylthiocarbamate) was included as a standard of comparison and provided satisfactory control of all weed species. Three-year averages of alfalfa (Medicago sativa L.) injury ratings at herbicide rates estimated to be equivalent in biological activity to 0.8 kg/ha and 1.7 kg/ha trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) respectively were: butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] 0% and 3%, benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) 2% and 9%, profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] 5% and 19%, AC92390 (N-sec-butyl-2,6-dinitro-3,4-xylidine) 6% and 17%, trifluralin 6% and 26%, fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline] 14% and 45%, and nitralin 18% and 49%. EPTC caused an average 4% injury at 3.4 kg/ha. At equivalent rates to 0.8 kg/ha trifluralin, most treatments caused an increase in first cutting alfalfa yields accompanied by a decrease in weed yields, except in 1974 when few treatments resulted in increased alfalfa yields. Alfalfa recovered from early season injury caused by higher rates of the herbicides, so that total alfalfa yields were usually not reduced compared to the control. Total herbage yields (alfalfa + weeds) were not increased by any treatment, and were sometimes decreased, especially by high rates of the herbicides.