Bio-efficacy and economics of herbicide mixtures in zero-till maize (Zea mays) grown after rice (Oryza sativa)

A field experiment was conducted at Warangal, Andhra Pradesh during 2008-09 and 2009-10 to study the ef- fect of pre-emergence application of herbicides viz. atrazine, glyphosate, paraquat and 2, 4-D sodium salt in zero- till maize ( Zea mays L.) grown after rice ( Oryza sativa L.) as sole and tank mixtures. The lowest density (no/m2) and dry weight (g/m2) of grasses (1.0 and 1.0, respectively), sedges (9.0 and 2.0, respectively) and broad- leaved weeds (1.0 and 0.5, respectively) were observed with the tank mix application of atrazine + glyphosate (0.75 + 0.8 kg/ha) recorded at 30 days after sowing. It was at par with atrazine + paraquat (0.75 + 0.75 kg/ha). The weed con- trol efficiency was high with atrazine + glyphosate (93%) with the lowest weed persistence index (0.003) followed by atrazine + paraquat (84% and 0.021, respectively). Among the herbicides applied alone, glyphosate (1.6 kg/ha) was found to be superior to atrazine (1.5 kg/ha) and paraquat (1.5 kg/ha) for density, dry weight of weeds and weed-control efficiency. The grain yield obtained with tank mix application of atrazine + glyphosate (5.25 t/ha) was 170 and 70% more over weedy check and sole atrazine, respectively. Among all the herbicides and mixtures, atrazine + glyphosate gave the maximum net returns ( 29,350/ha) and benefit : cost ratio (1.71) fol- lowed by atrazine + paraquat due to the broad - spectrum control of weeds.