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Christopher R. Johnston and Gerald M. Henry

Dallisgrass control in response to various timings and frequencies of single and combination herbicide treatments was evaluated from 2010 to 2012 in Lubbock, TX. Treatments included thiencarbazone-methyl + foramsulfuron + halosulfuron-methyl (TFH) at 15 + 31 + 47 or 22 + 45 + 70 g a.i./ha, foramsulfuron at 106 g a.i./ha, and foramsulfuron + thiencarbazone-methyl + iodosulfuron-methyl-sodium + dicamba (foramsulfuron + TID) at 106 + (22 + 5 + 147) g a.i./ha. Applications of TFH provided ≤65% dallisgrass control by 10 weeks after initial treatment (WAIT) across two rates (15 + 31 + 47 or 22 + 45 + 70 g a.i./ha) and three application timings [September, October, or September followed by (fb) a sequential October application]. At 37 WAIT, sequential applications of TFH at 15 + 31 + 47 g a.i./ha resulted in 92% dallisgrass control. Similarly, application of TFH at 22 + 45 + 70 g a.i./ha provided 94% and 97% dallisgrass control when applied in September or September fb October, respectively. However, single October applications of TFH only provided ≤55% dallisgrass control 37 WAIT. Sequential combinations of foramsulfuron + TID at 106 + (22 + 5 + 147) g a.i./ha provided 93% dallisgrass control 37 WAIT, equivalent to single applications of TFH at 15 + 31 + 47 g a.i./ha and sequential treatments at 15 + 31 + 47 or 22 + 45 + 70 g a.i./ha. However, initial control (10 WAIT) with foramsulfuron + TID was moderate (63%). Sequential foramsulfuron applications (106 g a.i./ha) resulted in inadequate dallisgrass control (35% and 48%) 10 and 37 WAIT, respectively. Results from this study suggest that long-term dallisgrass control may be achieved when TFH is applied in September or September fb October. Applications initiated in October resulted in inadequate control, regardless of rate, which may be linked to reduced herbicidal absorption and translocation due to the onset of dallisgrass dormancy in late fall. Chemical names used: methyl 4-[(4,5-dihydro-3-methoxy-4-methyl-5-oxo-1H-1,2,4-triazol-1-yl)carbonylsulfamoyl]-5-methylthiophene-3-carboxylate (thiencarbazone-methyl); 2-[(4,6-dimethoxypyrimidin-2-yl)carbamoylsulfamoyl]-4-formamido-N,N-dimethylbenzamide (foramsulfuron); methyl 3-chloro-5-[(4,6-dimethoxypyrimidin-2-yl)carbamoylsulfamoyl]-1-methylpyrazole-4-carboxylate (halosulfuron-methyl); sodium (5-iodo-2-methoxycarbonylphenyl)sulfonyl-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)carbamoyl]azanide (iodosulfuron-methyl-sodium); and 3,6-dichloro-2-methoxybenzoic acid (dicamba).