Broadleaf Weed Control in Ultra Narrow Row Bromoxynil-Resistant Cotton (Gossypium hirsutum)1

Abstract

A field experiment was conducted over 2 yr to study efficacy of bromoxynil mixtures with pyrithiobac or MSMA applied postemergence (POST) with and without fluometuron or fluometuron plus pendimethalin preemergence (PRE) for control of broadleaf weeds in ultra narrow row bromoxynil-resistant cotton in the Mississippi Delta. Bromoxynil applied POST (single or sequential) provided variable control of common purslane (<9%), sicklepod (<35%), Palmer amaranth (<46%), prickly sida (>75%), hyssop spurge (>79%), hemp sesbania (>96%), and pitted morningglory (100%) at 4 wk after early POST (WAT). Broadleaf weed control increased when PRE herbicides were followed by bromoxynil or bromoxynil plus pyrithiobac or MSMA POST. Weed control generally decreased at harvest compared to 4 WAT, and the decrease was greater in bromoxynil POST-only programs compared to bromoxynil POST following PRE programs. Seed cotton yield with bromoxynil POST-only programs was lower (400 to 2,810 kg/ha) compared to bromoxynil POST programs following PRE herbicides (2,150 to 3,720 kg/ha). Early-season weed interference and variable control of weeds in bromoxynil POST-only programs resulted in greater cotton stand reduction and lower open bolls per plant compared to bromoxynil POST programs following PRE herbicides.Nomenclature: Bromoxynil; fluometuron; MSMA; pendimethalin; pyrithiobac; common purslane, Portulaca oleracea L. #3 POROL; cotton, Gossypium hirsutum L. ‘BXN 47’; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; hyssop spurge, Euphorbia hyssopifolia L. # EPHHS; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin & Barneby # CASOB.Additional index word: Transgenic cotton.Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; POST, postemergence; PRE, preemergence; UNR, ultra narrow row; WAT, weeks after EPOST application.