Persistence of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of alachlor and acetochlor, as well as EC formulations of metolachlor, s-metolachlor, dimethenamid, and flufenacet were studied using a bioassay based on root response of oat Kassandra grown in soil. Flufenacet was the most persistent of the herbicides, but biologically available residues were not detected at 0- to 10-cm soil depth 50 d after any herbicide treatment. All herbicides applied preemergence (PRE) in field trials gave good to excellent control of redroot pigweed, black nightshade, barnyardgrass, and green foxtail but only partial control of jimsonweed. Furthermore, when they were applied postemergence (POST) in mixture with atrazine in the field, the control obtained for black nightshade, common lambsquarters, common purslane, and redroot pigweed was excellent, but good to excellent for bristly foxtail and green foxtail. Their efficacy against yellow foxtail and large crabgrass was fair to good. Generally, the EC-alachlor and EC-acetochlor applied POST in mixture with atrazine gave better control of grasses than did their ME-formulations. None of the herbicide treatments showed any phytotoxic effect on corn, and all of them produced corn yield greater than that of weedy control but slightly lower than that of the weed-free control. Flufenacet, s-metolachlor, and dimethenamid were suitable alternatives to acetochlor, alachlor, and metolachlor.
Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; black nightshade, Solanum nigrum L. # SOLNI; bristly foxtail, Setaria verticillata (L.) Beauv. # SETVE; common lambsquarters, Chenopodium album (L.) # CHEAL; common purslane, Portulaca oleracea L. # POROL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; jimsonweed, Datura stramonium L. # DATST; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; redroot pigweed, Amaranthus retroflexus L. # AMARE; yellow foxtail, Setaria glauca (L.) Beauv. # SETLU; corn, Zea mays L. ‘Pioneer Costanza’, ‘Pioneer Eleonora’, ‘Shell Nikerson’; oat, Avena sativa L. ‘Kassandra’.
Additional index words: Acetochlor, alachlor, dimethenamid, flufenacet, s-metolachlor, microencapsulated formulations.
Abbreviations: DAT, days after treatment; EC, emulsifiable concentrate; ME, microencapsulated; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.
