Palmer Amaranth and Texas Millet Control in Bollgard II® Xtendflex™ Cotton

As glyphosate-resistant Palmer amaranth continues to spread across the Texas High Plains, growers are anticipating new cotton technologies to assist in their weed management strategies. Bollgard II® Xtendflex™ cotton is a three-way herbicide tolerance stack with tolerance to dicamba (Clarity®), glyphosate (Roundup®), and glufosinate (Liberty®). Field trials were conducted at the Texas Tech University Research Farm near New Deal, Texas and at the Texas A&M AgriLife Research Farm near Halfway, Texas in 2013 and 2014.  Test species included Palmer amaranth (Amaranthus palmeri S. Wats.) and Texas millet (Urochloa texana Buckl.). Weed management treatments included systems with and without trifluralin preplant incorporated (PPI); acetochlor (Warrant™), acetochlor plus XtendiMax™ (a new formulation of dicamba), or no herbicide applied preemergence (PRE); and glufosinate, glufosinate plus XtendiMax™, Roundup® Xtend (dicamba plus glyphosate), glyphosate, or glyphosate plus acetochlor applied early-postemergence (EPOST), mid-postemergence (MPOST), and/or late-postemergence (LPOST); and diuron (Direx) plus glyphosate at layby. Several effective weed management systems were identified in Bollgard II® XtendFlex^TM cotton. Trifluralin and acetochlor were effective “foundations” for control of Palmer amaranth and Texas millet, which reduced weed emergence and crop competition with less reliance on postemergence herbicides.