Antagonism of BAS 625 by selected broadleaf herbicides and the role of ethanol

Greenhouse and laboratory research was conducted to determine the antagonistic effects of various tank mixtures on BAS 625 efficacy. Bensulfuron at 60 g ai ha⁻¹ and BAS 635 at 40 g ai ha⁻¹ did not antagonize control of Echinochloa crus-galli or Brachiaria platyphylla by BAS 625 at 30 g ai ha⁻¹ in greenhouse experiments. Tank mixtures of BAS 625 with 1,000 g ai ha⁻¹ bentazon reduced BAS 625 control of E. crus-galli from 100 to 40%. Antagonism of BAS 625 activity by bentazon or chlorimuron at 10 g ai ha⁻¹ was similar with B. platyphylla, reducing control from 100 to 28 and 32%, respectively. Addition of 5% (v//v) ethanol eliminated all antagonism with any of the herbicides used with either weed species. Uptake and translocation of ¹⁴C-BAS 625 1 and 12 h after treatment was not enhanced, either alone or in tank mixtures, with the addition of ethanol. Uptake of ¹⁴C-BAS 625 1 and 12 h after treatment was lower in both species when tank-mixed with bentazon. There was no effect of any of the antagonizing herbicides or ethanol on the metabolic degradation of the BAS 625 that was taken up by the plant. The herbicide concentration for 50% inhibition of activity (I₅₀) for BAS 625 on Triticum aestivum acetyl coenzyme A carboxylase (ACCase) was 125 µM. Bentazon, BAS 635, and NC-311 at 1 mM each did not alter the inhibition on ACCase by BAS 625. BAS 635, NC-311, and bentazon at 1 mM inhibited the activity of ACCase 12, 16, and 29%, respectively. Our results indicate that antagonism of the weed control activity of BAS 625 by bentazon may be partly caused by reduced uptake. Other mechanisms may be involved to explain the antagonism of BAS 625 by bentazon and the sulfonylurea herbicides used in this study.Nomenclature: BAS 625, Lithium 2-[1-(2-(4 chlorophenoxy)propoxyimino)butyl]-3-oxo-5-thian-3-ylcyclohex-1-enolate; BAS 635, 1-[(4-methoxy-6-trifluoromethyl)-1,3,5-triazin-2-yl]-3-(2-trifluoromethylbenzenesulfonyl)urea; bensulfuron; bentazon; chlorimuron; NC-311, ethyl 5-(4,6-dimethoxypyrimidin-2-ylcarbamoyl sulfamoyl)-1-methylpyrazole-4-carboxylate; Triticum aestivum L. emend. Thell., wheat; Echinochloa crus-galli (L.) Beauv. ECHCG, barnyardgrass; Brachiaria platyphylla (Griseb.) Nash BRAPP, broadleaf signalgrass.