Successful weed control before planting cotton (Gossypium hirsutum L.) in reduced tillage systems minimizes early-season weed interference. Field experiments were conducted in 1994 and 1995 in Louisiana to compare Italian ryegrass control by glyphosate at 0.84 kg ae ha-1 or paraquat at 0.53 kg ai ha-1 applied at eight growth stages ranging from the two-leaf stage through heading. Applications were spaced 1 wk apart. In a second experiment conducted in Louisiana in 1995 and 1996, glyphosate (0.56 kg ha-1) or paraquat (0.53 kg ha-1) were applied alone or with oxyfluorfen (0.22 kg ai ha-1), cyanazine (0.56 kg ai ha-1), cyanazine plus commercial package mixture of thifensulfuron plus tribenuron (0.56 + 0.024 + 0.008 kg ai ha-1), thifensulfuron plus tribenuron (0.024 + 0.008 kg ha-1), and 2,4-D (0.75 kg ai ha-1). In a final experiment conducted in 2000 in North Carolina, glyphosate (0.84 kg ha-1) and paraquat (0.53 kg ha-1) efficacy was compared with efficacy of clethodim applied at 0.14, 0.21, and 0.28 kg ai ha-1. Glyphosate was more effective in controlling Italian ryegrass than paraquat at most growth stages. However, when comparing efficacy of these herbicides in the tank mixture experiment or in the experiment comparing efficacy with clethodim, control by paraquat and glyphosate did not differ. Cyanazine and cyanazine plus thifensulfuron plus tribenuron reduced control by glyphosate but not control by paraquat. Oxyfluorfen, thifensulfuron plus tribenuron, and 2,4-D did not affect control by glyphosate or paraquat. Clethodim was more effective than glyphosate or paraquat in one of two experiments.
