Evaluation of Post Applied S-metolachlor in Combination with Glufosinate in Cotton (Gossypium hirsutum)

Abstract

Studies were conducted in Alabama in 2016 and 2017 to determine the effect of postemergence applications of glufosinate alone and glufosinate applied with S-metolachlor, using two different nozzle types, on LibertyLink®, Xtend®, and WideStrike® cotton. Field trials consisted of two applications of glufosinate at 0.6 kg ha-1, and glufosinate with S-metolachlor at 1.39 kg ha-1 applied to each cotton cultivar at the four-leaf and eight-leaf growth stages using a flatfan and Turbo TeeJet Induction® nozzle. Visual estimates of cotton injury were evaluated after each application, as well as yield. No differences in yield, within each cotton cultivar were observed for either year. Visual injury was higher for WideStrike cotton than LibertyLink or Xtend cultivars. On average, glufosinate applied with S-metolachlor resulted in higher injury than glufosinate applied alone. In some instances, applications made with TTI nozzles resulted in greater injury than flatfan nozzles. Greenhouse studies were conducted to determine the effects of applications on gas exchange measurements such as CO2 assimilation and stomatal conductance. There were no differences between gas exchange measurements in LibertyLink, and Xtend cotton following herbicide treatments. CO2 assimilation and stomatal conductance in WideStrike cotton significantly decreased following herbicide application, regardless of herbicide treatment or nozzle type. Gas exchange measurements of WideStrike cotton fully recovered to levels equal to or greater than the nontreated cotton by seven days after treatment. These data indicate that applications of glufosinate and glufosinate applied with S-metolachlor, at 0.6 kg ha-1 and 1.39 kg ha-1, respectively, with either a flatfan or TTI nozzle, made under certain conditions can have no detrimental effect on cotton growth, yield, or the plant processes of photosynthesis or leaf conductance past seven days.