| The introduction of genetically altered herbicide-tolerant varieties has lead to advances in cotton (Gossypium hirsutum L.) weed management. Bromoxynil-tolerant cotton (BXN cotton) was introduced in 1995. While BXN cotton has excellent tolerance to bromoxynil, the spectrum of weed control obtained with bromoxynil is relatively limited. Subsequently, Roundup Ready and Liberty Link cotton were introduced. These varieties can tolerate the nonselective herbicides glyphosate and glufosinate, respectively.;Multi year field studies were conducted at two Alabama locations to compare weed management between Roundup Ready and Liberty Link cotton systems and to determine the tolerance of Liberty Link cotton to glufosinate. Tolerance results to glufosinate-tolerant cotton showed that early-, mid- or late-season applications, regardless of rate, had no adverse effects on seed cotton yield.;A separate field experiment was conducted at Tallassee, AL to evaluate response of Liberty Link cotton to glufosinate, applied either alone or in tank mix with other herbicides traditionally used for Cyperus spp. control in cotton, i.e. norflurazon and pyrithiobac PRE, and DSMA and MSMA postemergence-applied (POT). Cotton varieties included a Liberty Link variety and the equivalent non-transgenic variety. Visual injury and yield suppression was evident with POT applications of MSMA and DSMA applied alone, or a tank mix of MSMA + glufosinate. However, when glufosinate application preceded MSMA or DSMA by 3 day, injury and yield suppression was reduced.;Field experiments were conducted at Tallassee, AL from 1998 through 2000 to evaluate the tolerance of four Roundup Ready cotton varieties to glyphosate and glyphosate + mepiquat chloride under weed-free conditions. The four varieties were: Deltapine (DP) 425, DP 5690, DP 655 and Paymaster (PM) 1220. Overall, each variety responded differently, and optimal yields were obtained when no glyphosate was applied. When glyphosate was applied, yield was less likely to be reduced when postemergence-directed after 4-L stage as opposed to an over-the top treatment after the 4-L stage. (Abstract shortened by UMI.)... |
