Field studies were conducted in Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, and Tennessee during 2010 and 2011 to determine the effect of glufosinate application rate on LibertyLink and WideStrike cotton. Glufosinate was applied in a single application (three-leaf cotton) or sequential application (three-leaf followed by eight-leaf cotton) at 0.6, 1.2, 1.8, and 2.4 kg ai ha⁻¹. Glufosinate application rate did not affect visual injury or growth parameters measured in LibertyLink cotton. No differences in LibertyLink cotton yield were observed because of glufosinate application rate; however, LibertyLink cotton treated with glufosinate yielded slightly more cotton than the nontreated check. Visual estimates of injury to WideStrike cotton increased with each increase in glufosinate application rate. However, the injury was transient, and by 28 d after the eight-leaf application, no differences in injury were observed. WideStrike cotton growth was adversely affected during the growing season following glufosinate application at rates of 1.2 kg ha⁻¹ and greater; however, cotton height and total nodes were unaffected by glufosinate application rate at the end of the season. WideStrike cotton maturity was delayed, and yields were reduced following glufosinate application at rates of 1.2 kg ha⁻¹ and above. Fiber quality of LibertyLink and WideStrike cotton was unaffected by glufosinate application rate. These data indicate that glufosinate may be applied to WideStrike cotton at rates of 0.6 kg ha⁻¹ without inhibiting cotton growth, development, or yield. Given the lack of injury or yield reduction following glufosinate application to LibertyLink cotton, these cultivars possess robust resistance to glufosinate. Growers are urged to be cautious when increasing glufosinate application rates to increase control of glyphosate-resistant Palmer amaranth in WideStrike cotton. However, glufosinate application rates may be increased to maximum labeled rates when making applications to LibertyLink cotton without fear of reducing cotton growth, development, or yield.

Nomenclature: Glufosinate; Palmer amaranth, Amaranthus palmeri S. Wats; cotton, Gossypium hirsutum L.

Estudios de campo fueron realizados en Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, y Tennessee durante 2010 y 2011 para determinar el efecto de la dosis de aplicación de glufosinate sobre algodón LibertyLink y WideStrike. Se aplicó glufosinate en una aplicación sencilla (algodón con tres hojas) o en aplicaciones secuenciales (algodón con tres hojas seguido de ocho hojas) a 0.6, 1.2, 1.8, y 2.4 kg ai ha⁻¹. La dosis de aplicación de glufosinate no afectó el daño estimado visualmente o los parámetros de crecimiento medidos en algodón LibertyLink. No se observaron diferencias en el rendimiento del algodón LibertyLink debido a la dosis de glufosinate. Sin embargo, el algodón LibertyLink tratado con glufosinate produjo un rendimiento ligeramente mayor que el testigo sin tratamiento. Estimaciones visuales de daño en el algodón WideStrike aumentaron con el incremento en la dosis de aplicación de glufosinate. Sin embargo, el daño fue transitorio, y a 28 d después de la aplicación a ocho hojas, no se observó ninguna diferencia entre dosis. El crecimiento del algodón WideStrike fue afectado adversamente durante la temporada de crecimiento después de las aplicaciones de glufosinate a dosis de 1.2 kg ha⁻¹ o mayores. Sin embargo, la altura del algodón y el total de nudos no fueron afectados por la dosis de aplicación de glufosinate al final de la temporada. La madurez del algodón WideStrike fue retrasada, y los rendimientos reducidos después de la aplicación de glufosinate a 1.2 kg ha⁻¹ o más. La calidad de la fibra de los