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

Greenhouse and laboratory research was conducted to determine the antagonis tic 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 nor antagonize control of Ec hinochloa 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%. Antagon ism of BAS 625 activity by bentazon or chlorimuron at 10 g ai ha(-1) was si milar with B. platyphylla, reducing control from 100 to 28 and 32%, respect ively. Addition of 5% (v/v) ethanol eliminated all antagonism with any of t he herbicides used with either weed species. Uptake and translocation of C- 14-BAS 625 1 and 12 h after treatment was not enhanced, either alone or in tank mixtures, with the addition of ethanol. Uptake of C-14-BAS 625 1 and 1 2 h after treatment was lower in both species when tank-mixed with bentazon . There was no effect of any of the ant agonizing herbicides or ethanol on the metabolic degradation of the BAS 625 that was taken up by the plant. Th e herbicide concentration for 50% inhibition of activity (I-50) for BAS 625 on Triticum aestivum acetyl coenzyme A carboxylase (ACCase) was 125 mu M. 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 acti vity of ACCase 12, 16, and 29%, respectively. Our results indicate that ant agonism of the weed control activity of BAS 625 by bentazon may be partly c aused by reduced uptake. Other mechanisms may be involved to explain the an tagonism of BAS 625 by bentazon and the sulfonylurea herbicides used in thi s study.