Master of Science (MS)
Plant, Enviromental and Soil Sciences
Field studies were conducted in 2011, 2012, and 2013 near Alexandria, LA to determine glufosinate rates and timings for control of rhizome johnsongrass [Sorghum halepense (L.) Pers.] in glufosinate-resistant soybean [Glycine max (L.)Merr.]. Johnsongrass control (75%) and height reduction (63%) throughout the season were greatest when glufosinate was applied at 0.7 kg ai ha-1 followed by (fb) 0.6 kg ha-1. Furthermore, following initial applications of glufosinate at 0.7 kg ha-1 (2670 kg ha-1) increased soybean yields were observed compared to 0.5 kg ha-1 (2400 kg ha-1), and soybean yields were greater following sequential glufosinate applications of 0.6 kg ha-1 followed by 0.5 kg ha-1. These data suggest that sequential applications of glufosinate is an option to control rhizomatous johnsongrass in glufosinate-resistant soybean. Additionally, field trials were conducted in 2011 and 2012 to assess control of johnsongrass in soybean with sequences of chlorimuron, clethodim, and fomesafen applied at early-post-emergence (EPOST), mid-postemergence (MPOST), and late-postemergence (LPOST). Sequential applications of glufosinate was added as a comparison treatment at all three timings. Clethodim applied EPOST was similar in johnsongrass control to sequentially applied glufosinate 35 days after LPOST. Johnsongrass control at harvest following sequential glufosinate applications (90%) or clethodim fb chlorimuron fb fomesafen (82%) did not differ. At harvest, differences in johnsongrass heights were not observed between treatments. Following sequentially applied glufosinate soybean yields were similar where clethodim was applied LPOST. Furthermore, trials were conducted to assess johnsongrass control in cotton [Gossypium hirsutum L.] in 2011, 2012, and 2013 following glufosinate applied two or three times sequentially, initiated 2, 3, or 4 wk after planting and sequential applications timed 2 or 3 wk apart. Johnsongrass control was maximized when three applications were applied at least 3 wk apart. However, johnsongrass control and reduction in heights was greatest when timing the initial application 4 WAP. Additionally, cotton yield was comparable to three total applications when two applications were made initiated 4 WAP.
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Landry, Randall Lee, "Control Options for Rhizome Johnsongrass (Sorghum halepense L. Pers.) in Glufosinate-Resistant Cotton (Gossypium hirsutum L.) and Soybean (Glycine max L. Merr.)" (2014). LSU Master's Theses. 26.