Pendimethalin plus pyrazosulfuron for pre-emergence control of complex weed flora in dry-seeded rice

Heavy weed infestation is one of the major constraints in dry-seeded rice. In North-West India, farmers use pendimethalin for pre-emergence control of grasses and small-seeded broad-leaf weeds, while bispyribac is used for post-emergence control of grasses. Continuous use of these herbicides has resulted in weed shift from annual grasses to broad-leaf weeds and sedges, and from annual weeds to perennial weeds particularly Cyperus rotundus. Field studies were carried out for successive three years (during 2016-18) in Kharif (rainy) season to evaluate pendimethalin plus pyrazosulfuron (pre-mix) at variable doses for pre-emergence control of grasses, sedges and broad-leaf weeds in dry-seeded rice. The uncontrolled growth of grasses, sedges and broad-leaf weeds in dry-seeded rice for whole crop season resulted in 68.7% reduction in crop yield. Pre-emergence application of pendimethalin plus pyrazosulfuron 1150 g/ha effectively reduced weed density and biomass of Digitaria sanguinalis, Dactyloctenium aegyptium, Echinochloa colona, Cyperus rotundus, C. iria, Phyllanthus niruri, Alternanthera philoxeroides, Mollugo nudicaulis and Digera arvensis with weed control efficiency of 85.3% up to 40 DAS. Though grain yield was maximum in weed free, pre-emergence use of pendimethalin plus pyrazosulfuron 1150 g/ ha resulted in the highest returns. Therefore, it was concluded that pendimethalin plus pyrazosulfuron 1150 g/ha as pre-emergence herbicide provided economical control of grasses, broad-leaf weeds and sedges in dry-seeded rice during early crop-weed competition period.