Torpedograss is a serious problem in southern turfgrass, especially along the U.S. gulf coast. Studies were conducted in 1999, 2000, 2002, and 2003 to evaluate single and sequential applications of trifloxysulfuron-sodium for torpedograss control in bermudagrass turf. In 1999/2000, single applications of trifloxysulfuron-sodium at 75 g ai/ha provided at least 10% better torpedograss control than 25 g/ha 7 and 15 wk after initial treatment (WAIT). When evaluated 15 WAIT, sequential applications of trifloxysulfuron-sodium provided 87% control, similar to 84% control observed with quinclorac diclofop-methyl, each applied at 840 g ai/ha. Both treatments controlled torpedograss better than a single trifloxysulfuron-sodium application (61%) in 1999/2000. Torpedograss control was less in 2002/2003 than in 1999/2000 because of high rainfall, which encouraged aggressive torpedograss growth and possible movement of trifloxysulfuron-sodium below its rooting zone. No differences were noted among trifloxysulfuron-sodium rates or number of applications in 2002/2003. Quinclorac diclofop-methyl controlled torpedograss greater than trifloxysulfuron-sodium 15 WAIT in 2002/2003, but neither treatment provided greater than 45% control. These results suggest that trifloxysulfuron-sodium controls torpedograss when rainfall is not excessive.
Nomenclature: Bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davey ‘Tifway’; torpedograss, Panicum repens L. #3 PANRE.
Additional index words: Application rate, application frequency.
Abbreviations: WAIT, weeks after initial treatment.