Influence of Glufosinate Timing on Cotton Growth and Yield

Glyphosate-resistant (GR) weeds are a major issue for Tennessee cotton growers and can be problematic to control and prevent yield loss.  GR horseweed, GR giant ragweed, and GR Palmer amaranth are the three GR weeds that can currently be found in Tennessee.  GR Palmer amaranth has become the most difficult to control of these.  As a result, many growers have moved to an Ignite-based system to manage GR weeds which includes a pre applied herbicide followed by at least one over-the-top Ignite application.  Liberty Link cotton varieties are planted on just a few acres in Tennessee due to inconsistent performance of these varieties in the state.  Over 60% of the cotton acres in Tennessee are planted to a WideStrike cotton variety which has tolerance to both glyphosate and glufosinate (Ignite).  The WideStrike cotton varieties have moderate tolerance to Ignite.  The injury range is typically in the 15 to 25% range.  However, this is for one application and growers are often using multiple applications throughout the growing season in order to control GR Palmer.  Growers often call asking how much injury one can encounter from repeated Ignite applications to WideStrike varieties.  Therefore a study was constructed that examined glufosinate applied one, two, or three times throughout the growing season at a rate of 29 oz/A.  Treatments were applied to cotton at the 2-leaf, 7-leaf, bloom, or two weeks after blooming stage.  The objective of this study was to determine if glufosinate applications at different timings affected cotton growth, development, and yield.