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 Cypereus esculentus L. (yellow nutsedge), and POST-only programs were as effective as PRE followed by POST programs.