Field experiments were conducted to evaluate weed control and cotton response to glyphosate or glufosinate applied alone or with residual herbicides applied in the last POST-directed application (LAYBY) in glyphosate- and glufosinate-resistant cotton. Glyphosate (0.86 kg ae/ha) or glufosinate (0.47 kg ai/ha) were applied alone over the top of glyphosate- or glufosinate-resistant cotton early POST (EPOST) followed by (fb) late POST (LPOST) fb one of the herbicides applied either alone or with a residual herbicide at LAYBY. Glyphosate- and glufosinate-based treatments were applied only to glyphosate- and glufosinate-resistant cotton, respectively. Residual herbicides evaluated included prometryn (1.12 kg ai/ha), fluometuron (1.12 kg ai/ha), diuron (1.12 kg ai/ha), oxyfluorfen (1.12 kg ai/ha), pendimethalin (1.0 kg ai/ha), prometryn trifloxysulfuron (1.33 kg ai/ha 12 g ai/ha), or linuron diuron (0.56 0.56 kg ai/ha). Glyphosate-and glufosinate-based weed management systems with and without residual LAYBY herbicides resulted in little to no injury to cotton. Three applications of glyphosate or glufosinate alone provided better full-season control of most species when compared to two applications of either herbicide. The addition of a residual herbicide to glyphosate or glufosinate at LAYBY did not improve cotton yields, but did improve overall control of barnyardgrass and yellow nutsedge and reduced weed dry biomass present at time of cotton harvest when compared to three applications of glyphosate or glufosinate alone.

Nomenclature: Diuron; fluometuron; glufosinate; glyphosate; linuron; oxyfluorfen; pendimethalin; prometryn; trifloxysulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; yellow nutsedge, Cyperus esculentus L. CYPES; cotton, Gossypium hirsutum L. ‘DPL 555BG/RR’, ‘Fibermax 958LL, 966LL, and 989RR’.