Weed Control in Established Alfalfa (Medicago sativa) with Postemergence Herbicides1

Abstract

Field experiments were conducted during 1998, 1999, and 2000 in Santa Fe, Argentina, to evaluate chlorimuron, clethodim, flumetsulam, 2,4-DB, glyphosate, and haloxyfop for control of broadleaf and grass weeds in established alfalfa. Herbicides were applied to alfalfa, 6 to 10 cm in height, after first or second cuttings. Clethodim and haloxyfop were highly effective against bermudagrass, barnyardgrass, and knotroot foxtail, and alfalfa yields were increased. 2,4-DB was effective against Scotch thistle, swinecress, turnipweed, and birdsrape mustard, but no effects were observed on alfalfa yields. Chlorimuron, flumetsulam, and glyphosate were effective against burning nettle, common chickweed, common lambsquarters, spiny cocklebur, and Persian speedwell, but they injured alfalfa and decreased yields.Nomenclature: Chlorimuron; clethodim; 2,4-DB; flumetsulam; glyphosate; haloxyfop; alfalfa, Medicago sativa (L.); barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHGA; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; birdsrape mustard, Brassica rapa (L.) # BRACA; burning nettle, Urtica urens (L.) # URTUR; common chickweed, Stellaria media (L.) Villars # STEME; common lambsquarters, Chenopodium album (L.) # CHEAL; knotroot foxtail, Setaria geniculata (Lam.) Beauv. # SETGE; Persian speedwell, Veronica persica Poir. # VERPE; Scotch thistle, Onopordum acanthium (L.); spiny cocklebur, Xanthium spinosum (L.) # XANSP; swinecress, Coronopus didymus Sm. # COPDI; turnipweed, Rapistrum rugosum (L.) All. # RASRU.Abbreviation: DAT, days after treatment.