Horseweed Control in Oklahoma Cotton

The widespread adoption of no-till cotton production (typically including glyphosate based weed control programs) has emphasized the difficulty producers face when trying to control horseweed with chemical applications.  The lack of both pre-season and in-season tillage requires producers to primarily depend on hormone-type herbicides (2,4-D or Dicamba) for effective control of horseweed due to the in-effectiveness of glyphosate applied alone.  Unfortunately, horseweed control programs including either 2,4-D or dicamba must be initiated several days before planting in order to avoid potential carryover issues.  Often times, new horseweed may re-emerge in this period prior to planting.  In order to achieve effective long-term, pre-plant control of horseweed, 2,4-D or dicamba must be tank-mixed with products providing effective residual control of horseweed without the potential for carryover or injury to newly planted cotton.  There are currently very few chemical options that fit these criteria.  Sharpen (saflufenacil) is a new product introduced by BASF which has the potential to provide both burn-down (post-emergence) as well as residual activity on horseweed.  In addition, suflafenacil also belongs to a class of chemistry (pyrimidinediones) which currently has no documented cases of chemical resistance.   Two replicated experiments were conducted in the spring of 2009 in order to explore the effectiveness of this product on horseweed when tank-mixed with either glyphosate, 2,4-D or dicamba.