| Abstract: | Field studies measured the response of sorghum (Sorghum bicolor L. "Conlee's Top Hand") to foliar applications of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]]oxy] phenoxy]propanoic acid} and the butyl ester of fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy]propanoic acid} (herein referred to as haloxyfop-methyl and fluazifop-P-butyl) alone and combined with bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid}, or chlorimuron {2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid}. Tank-mixing imazaquin or chlorimuron with haloxyflop-methyl or fluazifop-P-butyl reduced sorghum phytotoxicity by 14 to 63% at 12 days after treatment (DAT) compared to haloxyfop-methyl or fluazifop-P-butyl applied alone. However, at 24 DAT, losses in activity from the mixtures ranged from 13 to 21%. Thus, much of the antagonism was delayed phytotoxicity rather than a permanent reduction. Increasing haloxyfop-methyl and fluazifop-P-butyl rates reduced the severity of the antagonism. Tank-mixing bentazon with haloxyfop-methyl or fluazifop-P-butyl did not reduce sorghum phytotoxicity compared to haloxyfop-methyl or fluazifop-P-butyl alone. Aqueous mixtures of haloxyfop-methyl or fluazifop-P-butyl, prepared alone and with bentazon, imazaquin, or chlorimuron were kept at 24 C and examined over an 8 h period. Combinations of these herbicides did not alter the ester or free acid levels of haloxyfop or fluazifop-P in mixtures and remained chemically stable over the 8 h period. Thus, chemical incompatibility was not a mechanism for the antagonism observed in the field. The effect of bentazon, imazaquin, or chlorimuron formulations on absorption and translocation of haloxyfop in sorghum leaves was examined. Nearly twice as much haloxyfop-methyl remained on the leaf surface at 6 hours after haloxyfop-methyl application with bentazon (51.8%) compared to application of haloxyfop-methyl alone (27.1%). Total haloxyfop-methyl absorption was also decreased when bentazon was added to treatment mixtures (43.4%) compared to haloxyfop-methyl applied alone (56.1%). Absorption of haloxyfop-methyl in the presence of imazaquin or chlorimuron was similar to haloxyfop-methyl applied alone. Haloxyfop translocation was lower when haloxyfop-methyl was applied with bentazon (6.4%), imazaquin (12.5%), or chlorimuron (12.0%) than when haloxyfop-methyl was applied alone (19.8%). |
|---|