Field research was conducted for 2 yr to determine the effect of reduced rates of glufosinate on growth and yield of non–glufosinate-resistant cotton. Rates of 3.4, 6.7, 13, 26.5, 52.5, and 105 g ha⁻¹, representing 0.008, 0.016, 0.031, 0.063, 0.125, and 0.25 of an effective use rate (420 g ha⁻¹), were applied to cotton at the two-, five-, or nine-node growth stage. Based on analysis of visual injury, cotton response decreased as application timing was delayed in one of the three experiments. Injury response was increased slightly with application at the five- compared with the two-node growth stage and was not significant for the latest application timing (nine-node stage) in two of three experiments. In two of the three experiments, plant height reduction response was lowest at the five-node stage and greatest at the nine-node stage. Regardless of application timing, plant dry weight was negatively affected only with the highest rate of glufosinate. Glufosinate application, based on node above white flower number and percent open boll, did not result in a delay in maturity. Final plant population was reduced in all experiments at the two-node application and in one of the three experiments at the five-node stage. Glufosinate application did not adversely affect final plant population when applied to nine-node cotton. Negative effects on cotton growth were not manifested in seedcotton yield reduction after glufosinate application.

Nomenclature: Glufosinate; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘DP33B’.