Economics and efficacy of weed management in Bollgard II XtendFlex cotton

Increasing populations of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) have increased weed management costs for Texas High Plains cotton producers. The introduction of Bollgard II XtendFlex (dicamba-tolerant) varieties and registration of dicamba formulations for postemergence use in cotton, combined with residual herbicides, can effectively control Palmer amaranth. It is estimated that 60-70% of the region’s cotton acreage was planted in Bollgard II XtendFlex varieties in 2019. Field studies were conducted in 2018 and 2019 at Lubbock to evaluate Palmer amaranth control and economics of weed management for XtendFlex, LibertyLink, Roundup Ready, and conventional cotton systems for irrigated and dryland production. Trifluralin was used as a preplant incorporated (PPI) treatment in all cotton production systems. Caparol was applied preemergence (PRE) in all systems, except for the XtendFlex PRE only system. The XtendFlex system included a tank mix of XtendiMax + Roundup PowerMax applied early postemergence (EPOST) and XtendiMax + Roundup PowerMax + Warrant applied mid postemergence (MPOST). LibertyLink systems included Liberty EPOST and Liberty + Warrant MPOST. In 2019, the Liberty Link system required tillage and hand-hoeing to control escaped weeds. Roundup Ready systems included Roundup PowerMax EPOST and Roundup PowerMax + Warrant MPOST and used hand-hoeing and tillage to control glyphosate-resistant Palmer amaranth. The conventional system utilized tillage and hand hoeing for in-season weed control and Warrant MPOST. The most consistent season-long Palmer amaranth control was achieved with the XtendFlex system in both irrigated and dryland production with 99-100% control in 2018. In irrigated production, greatest lint yields were achieved with XtendFlex when compared to the conventional and LibertyLink systems. In 2018, greatest gross margin above weed management costs were achieved with the XtendFlex system in irrigated production. All systems produced yields in dryland cotton production and gross margin above weed management costs that were not different across dryland production systems in 2018. Total variable costs were not different across all systems, with greater seed/technology and herbicide costs in XtendFlex and Liberty Link systems, compared to higher tillage and hand hoeing costs in Roundup Ready and conventional systems in 2018 and 2019. The most consistent season-long Palmer amaranth control was achieved with the XtendFlex system in both irrigated and dryland production in 2019 when compared to the LibertyLink and Roundup Ready systems. In 2019, the XtendFlex and conventional systems resulted in similar gross margins but the XtendFlex system was the only systems to produce positive gross margin above weed management costs.