Weed Control and Crop Response to Glufosinate Applied to ‘PHY 485 WRF’ Cotton

Abstract

Field experiments were conducted in Georgia to evaluate weed control and crop tolerance with glufosinate applied to ‘PHY 485 WRF®’ cotton. This glyphosate-resistant cotton also contains a gene, used as a selectable marker, for glufosinate resistance. Three experiments were maintained weed-free and focused on crop tolerance; a fourth experiment focused on control of pitted morningglory and glyphosate-resistant Palmer amaranth. In two experiments, PHY 485 WRF cotton was visibly injured 15 and 20% or less by glufosinate ammonium salt at 430 and 860 g ae/ha, respectively, applied POST two or three times. In a third experiment, glufosinate at 550 g/ha injured cotton up to 36%. Pyrithiobac or glyphosate mixed with glufosinate did not increase injury compared to glufosinate applied alone;S-metolachlor mixed with glufosinate increased injury by six to seven percentage points. Cotton injury was not detectable 14 to 21 d after glufosinate application, and cotton yields were not reduced by glufosinate or glufosinate mixtures. A program of pendimethalin PRE, glyphosate applied POST twice, and diuron plus MSMA POST-directed controlled glyphosate-resistant Palmer amaranth only 17% late in the season.S-metolachlor included with the initial glyphosate application did not increase control, and pyrithiobac increased late-season control by only 13 percentage points. Palmer amaranth was controlled 90% or more when glufosinate replaced glyphosate in the aforementioned system. Pitted morningglory was controlled 99% by all glufosinate programs and mixtures of glyphosate plus pyrithiobac. Seed cotton yields with glufosinate-based systems were at least 3.3 times greater than yields with glyphosate-based systems because of differences in control of glyphosate-resistant Palmer amaranth.

Glufosinate Safety in WideStrike® Acala Cotton

“…The injury levels at various growth stages with 0.59 kg ha À1 glufosinate in our study were lower than in the studies of Culpepper et al (2009), who reported up to 36% injury with glufosinate at 0.59 kg ha À1 at various growth stages. The greatest level of injury with glufosinate at 0.59 kg ha À1 in our study was 21% in 1 yr when it was applied to twonode cotton.…”

“…Cotton yield parameters such as gin turnout and lint yield were not affected by the treatments in both years of the study (Table 3) and glyphosate at 0.84 kg ha À1 when these treatments were applied at the two-leaf stage of cotton. Culpepper et al (2009) reported 3.3 times greater seed-cotton yield with glufosinate-based than glyphosate-based systems in WideStrike cotton, but they attributed this difference to better control of GR Palmer amaranth with glufosinate. No cases of GR weeds were present in our research plots, so ineffective weed control was not a possible factor in reducing lint yield.…”

Long‐term Management of Palmer Amaranth with Herbicides and Cultural Practices in Cotton

“…Removal of weeds in these experiments occurred well after the critical period of weed interference (Fast et al, 2009). Lack of differences in yield due to deep tillage are consistent with results reported by Culpepper et al (2009b), where deep tillage did not impact yield when an effective herbicide program was implemented. Although a significant interaction was noted in 2014 for location × deep tillage treatment × hand‐removal, no difference was observed for cotton yield when analyzed by individual location (data not shown); therefore, data were pooled over locations.…”

Glufosinate Application Timing and Rate Affect Peanut Yield

“…Liberty-LinkH cotton cultivars were commercialized in 2004 (Duke 2005). Additionally, WideStrikeH cotton cultivars, which also contain the pat gene, are commercially available but offer lower levels of resistance to glufosinate (Culpepper et al 2009, Steckel et al 2012. In soybean, regulatory approval for glufosinate-resistance in soybean occurred in 1996 (Duke 2005).…”