Weed Management in Transgenic Soybean Resistant to Glyphosate Under Conventional Tillage and No-Tillage Systems.

A 3-year field research was conducted in 1997, 1998, and 1999 at Stoneville, MS on a Dundee silt loam soil to study efficacy and economics of glyphosate with or without preemergence (PRE) herbicides in glyphosate-resistant soybean under conventional tillage (CT) and no-tillage (NT) systems. Single or sequential glyphosate postemergence (POST) applications provided at least 91% control of Echinochloa crusgalli (L.) Beauv. (barnyardgrass), Brachiaria platyphylla (Griseb.) Nash (broadleaf signalgrass), Brachiaria ramosa (L.) Stapf (browntop millet), Sesbania exaltata (Raf.) Rydb. ex A.W. Hill (hemp sesbania), Sorghum halepense (L.) Pers. (johnsongrass), Senna obtusifolia (L.) Irwin and Barneby (sicklepod), Ipomoea lacunosa L. (pitted morningglory), Sida spinosa L. (prickly sida), and Cyperus esculentus L. (yellow nutsedge), and POST-only programs were as effective as PRE followed by POST programs. Two POST applications of glyphosate produced highest soybean yield (2,710 kg/ha) and net return ($280/ha). Single POST application of glyphosate resulted in greater net return ($226/ha) compared to the conventional standard (pendimethalin, imazaquin, acifluorfen, bentazon, and clethodim) herbicide program ($58/ha), although both had similar yields. Addition of PRE herbicides tend to increase herbicide costs and decrease net returns compared to two POST applications of glyphosate. Soybean yield and net return were lower in NT compared to CT systems, due to a lower soybean stand establishment in NT systems. These results suggest that when yields are comparable among various herbicide programs, net return is dictated by the cost of the herbicide program, including seeds and associated technology fee. [ABSTRACT FROM PUBLISHER]