Comparative Efficacy of Two Formulations of Alachlor and Metolachlor

Abstract

The efficacies of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were compared in petri dish and soil bioassays. At equimolar concentrations, EC-alachlor inhibited shoot growth of barnyardgrass[Echinochloa crus-galli(L.) Beauv. # ECHCG], large crabgrass[Digitaria sanguinalis(L.) Scop. # DIGSA], and fall panicum (Panicum dichotomiflorumMichx. # PANDI) more than ME-alachlor. ME- and EC-metolachlor caused similar effects on the three grass weeds tested. ME- and EC-alachlor in combination caused effects on barnyardgrass shoot growth intermediate to results with either formulation alone. Air-drying and remoistening of alachlor-treated filter paper or soil before sowing barnyardgrass or fall panicum caused greater shoot length and fresh weight reduction than ME-alachlor that was not dried.