Effects of Chlorsulfuron or 2,4-D upon Diclofop-Methyl Efficacy in Oat (Avena sativa)

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Abstract
Oat (Avena sativaL. ‘Elgin′) seedlings were treated with combinations of diclofop-methyl {methyl ester of 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} and 2,4-D amine [dimethylamine salt of (2,4-dichlorophenoxy) acetic acid] or diclofop-methyl and chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1, 3, 5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} to determine the effect of the added herbicide on diclofop-methyl activity. Diclofop-methyl applied alone at rates of 0.50, 0.75, and 1.00 kg/ha killed the oat plants 14 days after treatment. When 2,4-D amine at 0.74 and 1.11 kg/ha was combined with diclofop-methyl, the phytotoxicity of diclofop-methyl was reduced. An antagonistic interaction between diclofop-methyl and 2,4-D was detected. Chlorsulfuron, applied alone, at 20, 40, or 60 g/ha did not affect the growth of oats. Chlorsulfuron additions did not affect the activity of diclofop-methyl. Diclofop-methyl reduced oat coleoptile elongation. Equimolar concentrations of diclofop-methyl and 2,4-D at or above 1 μM significantly reduced the 2,4-D response. A ten-fold increase of either 2,4-D or diclofop-methyl, above an equimolar concentration of 1 μM, significantly enhanced the effect of the herbicide being increased.