Field experiments were conducted in 1998 and 1999 at two locations in Mississippi to determine weed control efficacy of postemergence soybean herbicides alone or following pendimethalin imazaquin preemergence in glufosinate-tolerant soybean planted in 38- or 76-cm rows. Glufosinate applications controlled pitted morningglory better than conventional herbicide treatments, regardless of row spacing. Pendimethalin imazaquin did not increase the efficacy of glufosinate on pitted morningglory. Pitted morningglory control was increased in narrow rows when compared to wide rows with all treatments. Sicklepod control ranged from 90 to 100% in narrow rows with glufosinate, regardless of rate. Residual herbicides alone controlled sicklepod 54%, regardless of row spacing. With grass species, two applications of 420 g ai/ha glufosinate controlled weeds 82 to 100%. Residual herbicides followed by 420 g/ha glufosinate controlled grass species 80% or more, regardless of row spacing. Hemp sesbania control ranged from 80 to 92% in 76- and 38-cm rows with one application of 560 g/ha glufosinate. Glufosinate at 420 g/ha used as sequential applications controlled hemp sesbania better than the conventional treatment in 76-cm rows. Residual herbicides in combination with glufosinate did not increase hemp sesbania control. There were no differences in yield due to row spacing at Stoneville in either year due to extremely dry growing conditions during pod set. At Starkville, two applications of 420 g/ha glufosinate resulted in higher yields than pendimethalin imazaquin followed by 420 g/ha glufosinate in both years. Pendimethalin imazaquin followed by 420 g/ha glufosinate increased yield in narrow rows compared to wide rows at Starkville in 1998.
Nomenclature: Glufosinate; imazaquin; pendimethalin; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill #3 SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; soybean, Glycine max (L.) Merr.
Additional index words: Glufosinate-tolerant soybean.
Abbreviations: POST, postemergence; POST-3, POST application 3 wk after planting; POST-5, POST application 5 wk after planting; PRE, preemergence; WAP, weeks after planting.
