Factors Affecting Postemergence Control of Sicklepod (Cassia obtusifolia) with Imazaquin and DPX-F6025: Spray Volume, Growth Stage, and Soil-Applied Alachlor and Vernolate

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Abstract
In field and greenhouse experiments, sicklepod (Cassia obtusifoliaL. # CASOB) control with postemergence application of imazaquin {ammonium salt of 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} was similar with spray volumes of 50, 185, and 360 L/ha. Application of DPX-F6025 {ethyl ester of 2-[[[[(4-chloro-6-methoxypyrimidin-2-yl) amino] carbonyl] amino] sulfonyl] benzoate} in 50 L/ha resulted in greater control than application in 185 or 360 L/ha in the greenhouse, but no effect of spray volume was noted in field studies. In the greenhouse, control was 25 and 63% less with imazaquin applied to three- and five-leaf plants, respectively, compared to one-leaf plants; control was 40 and 62% less with DPX-F6025 applied to three- and five-leaf plants, respectively, compared to one-leaf plants. In the field, initial control was greater with imazaquin and DPX-F6025 applied to one-leaf plants than to three- or five-leaf plants. Following cultivation, control was similar regardless of plant size at time of application. In the field, postemergence applications of imazaquin and DPX-F6025 were equally phytotoxic following preplant-incorporated application of vernolate (S-propyl dipropylcarbamothioate) or preemergence application of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide]. A synergistic interaction was observed in the greenhouse with imazaquin applied postemergence to sicklepod grown in vernolate- or alachlor-treated soil and with DPX-F6025 applied to sicklepod grown in alachlor-treated soil. Antagonism was observed with DPX-F6025 applied postemergence to sicklepod grown in vernolate-treated soil.