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Activity of Sulfonylurea Herbicides on Three Cultivars of Old World Bluestem Seedlings (Bothriochloa Spp.)

Williams, Kirk Wayne
The effects of four sulfonylurea herbicides at five rates on Old World bluestem seedlings ~ere compared in greenhouse experiments. Rates required to reduce seedling growth by 50% (GRso) were calculated and the minimum rate for weed control of each herbicide were compared on three Old World bluestem cultivars. Herbicides evaluated included chlorsulfuron, metsulfuron, CGA-131036, and CGA-136872 and cultivars treated included Caucasian, Plains, and WW Spar. Postemergence and preemergence applications of the herbicide use rate of chlorsulfuron caused more reduction in all growth parameters measured than the herbicide use rate of metsulfuron. Caucasian was more tolerant to both herbicides than Plains and WW Spar. Preemergence GRso values were closer to use rates for both metsulfuron and chlorsulfuron than postemergence GRso values. The herbicide use rate of CGA-136872 caused more growth reduction than the herbicide use rate of CGA-131036. All cultivars responded similarly to CGA-136872 while Caucasian and Plains were more tolerant of CGA-131036. Metsulfuron and CGA-131036 caused less growth reduction than either chlorsulfuron or CGA-136872. Nomenclature: Bothriochloa ischaemum var. ischaemum (L.) Keng. 'Plains' # DIHIS1 ; Bothriochloa ischaemum var. ischaemum (L.) Keng. 'WW Spar'; Bothriochloa caucasica (Trin.) C.E. Hubbard 'Caucasian'; chlorsulfuron, 2-chloro- N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide; metsulfuron, 2-[[[[(4-methoxy-6-methyl- 1,3,5-triazin-2-yl)amino]carbonyl] amino]sulfonyl]benzoic acid; CGA-131036, N-(6-methoxy-4-methyl-1,3,5-triazin-2-ylaminocarbonyl)- 2-(2-chlorethoxy)-benzenesulfonamide; CGA-136872, 2-[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl] amino]carbonyl]amino]sulfonyl] benzoic acid methyl ester. Additional index words. Herbicide injury, growth reduction, forage grass seedlings, chlorsulfuron, metsulfuron, CGA- 131036, CGA-136872. Andropogon spp., DIHIS