Managing glyphosate-resistant (GR) horseweed in no-till cotton continues to be a serious challenge for midsouthern producers. Field studies were conducted in 2008 and 2009 to evaluate spring burndown applications of saflufenacil on GR horseweed prior to planting cotton. Saflufenacil controlled GR horseweed at least 94% up to 7 d before planting (DBP) without causing significant cotton injury. Saflufenacil applied at 7 or 14 DBP controlled GR horseweed while still providing residual control until planting. Moreover, saflufenacil, on silt loam soil evaluated in this study, showed no more injury than dicamba applied 7 or more DBP. Results indicated that saflufenacil is an option in cotton for controlling GR horseweed much closer to cotton planting than 42 DBP (current saflufenacil label). At 25 g ha−1, which is the standard labeled rate in cotton, saflufenacil provided > 90% control of GR horseweed. Saflufenacil as a GR horseweed burndown, could replace the current dicamba standard every other year to reduce the probability of horseweed developing resistance to dicamba or salflufenacil.
Nomenclature: Horseweed, Conyza canadensis (L.) Cronq. ERICA; cotton, Gossypium hirsutum L. Phytogen 485WRF