Comparison of Trifloxysulfuron and Pyrithiobac in Glyphosate-Resistant and Bromoxynil-Resistant Cotton

Abstract

Field studies were conducted in 2000 and 2001 at Rohwer, AR. Trifloxysulfuron (5.3 and 8 g ai/ha) and pyrithiobac (70 g ai/ha) were applied preemergence (PRE) and postemergence (POST) broadcast at the two- to three-leaf (EP) and three- to four-leaf (MP) cotton growth stages. Both materials were also applied POST in combination with glyphosate at 560 g ae/ha or bromoxynil at 560 g ai/ha at both growth stages. Trifloxysulfuron applied EP or MP at 8 g/ha provided greater control of sicklepod and pitted morningglory 28 d after application (DAA) than trifloxysulfuron at 5.3 g/ha or pyrithiobac at 70 g/ha; however, control of prickly sida was greater with pyrithiobac than with trifloxysulfuron at either rate. Glyphosate alone controlled sicklepod, prickly sida, and pitted morningglory greater than 80%. The addition of trifloxysulfuron at 8 g/ha and pyrithiobac at 70 g/ ha increased control of all species over glyphosate alone 28 DAA. Bromoxynil at 560 g/ha controlled pitted morningglory and hemp sesbania at all application timings; however, sicklepod and Palmer amaranth control was less than 50% with bromoxynil applied alone. When bromoxynil was applied in combination with trifloxysulfuron at either rate, control of sicklepod and Palmer amaranth increased to 80% or greater at all application timings. Trifloxysulfuron has the potential to complement both the glyphosate-resistant and bromoxynil-resistant weed control programs by providing control of less susceptible weeds and by providing residual control to both programs.