Comparing Glufosinate Herbicide Tolerance of Widestrike and Liberty-Link Cotton Varieties

One option currently being utilized by growers in the Southeast is applying glufosinate topically to cotton varieties containing Widestrike™ technology.  Widestrike™ varieties (DAS-21023-5 x DAS-24236-5) contain two endotoxins for lepidopteran pests.  Widestrike™ varieties were developed by cross-breeding a transgenic line (DAS-21023-5) which produces Cry1Ac and a transgenic line (DAS-24236-5) which produces Cry1F.  Both of these events utilize the phosphinothricin acetyltransferase (pat) which was inserted as a selectable marker during plant transformation (Culpepper et al. 2009). The pat gene also confers resistance to glufosinate. Research has shown up to 35% phytotoxic injury of ‘PHY 485 WRF’ following topical applications of glufosinate.  However, little to no data is available regarding tolerance of other Widestrike™ varieties to topical applications of glufosinate.  Five Widestrike™ (PHY 367WRF, PHY 375WRF, PHY 440W, PHY 499WRF, and PHY 565WRF) and three Liberty Link™ (ST 4145LLB2, FM 1773LLB2, and FM 1845LLB2) cotton varieties were planted in a split-block design with four replications.  Plots consisted of four rows, 40 feet in length.  Each variety was sprayed with the maximum allowable in-season rate of glufosinate based upon the Ignite 280 SL label for Liberty Link™ cotton (2 applications at 0.53 lb ai/ac each).  In addition, each variety will have a complimentary untreated check for comparison purposes.  Glufosinate applications will be made to 1- to 3-leaf and 7- to 9-leaf cotton.  In a second study, two cotton varieties (PHY 375 WRF and FM 1773 LLB2) were planted in a split-plot design with four replications.  Each variety received a single and two applications of glufosinate at the following rates:  0.53 lb ai/ac (1X), 1.06 lb ai/ac (2X), 1.59 lb ai/ac (3X), and 2.39 lb ai/ac (4X).  Glufosinate applications will be made to 1 to 3- leaf and/or 7 to 9- leaf cotton.