EFFECTS OF HERBICIDES ON WEED SUPPRESSION AND RICE YIELD IN TRANSPLANTED WETLAND RICE

Eight herbicides, i.e. oxadiazone, butachlor, pretilachlorand anilphos from pre-, and MCPA, ethoxysulfuran,pyrazosulfuran Ethyl and oxadiarzil from post-emergencecategory were applied at recommended rates in transplanted wetland rice during aman (autumn), aus (summer) and boro(winter) growing seasons at Bangabandhu Sheikh MujiburRahman Agricultural University, Gazipur, Bangladesh (BSMRAU)during 2007-08 to study their effects on weed control and riceyield. Results revealed variations in the performance of herbicides in different seasons. Pre-emergence herbicides performed better regarding weed control efficiency and rice yield.Based on the initial performance, butachlor and MCPA were further applied at concentrations ranging from 50% to 150% of the recommended rates in transplanted aus rice in 2009. Dataindicated that butachlor provided better weed control efficiency and contributed to better crop growth and grain yield comparedto MCPA irrespective of concentration. It might be due to that pre-emergence application of Butachlor provided effective early season weed control, which MCPA could not since apply as postemergence.The highest grain yield of 4.18 t ha-1 was contributedby weed free treatment, while the least (2.44 t ha-1) was by weedy check. Among the herbicide treatments, the highest grain yield of 4.08 t ha-1 was obtained from butachlor, while the lowest(2.83 t ha-1) grain production was harvested in the plots receiving MCPA @ 125% of the recommended rate. Results further revealed a positive relationship between butachlor rateand grain yield, although a declining trend was apparent at higher than the recommended rates, while a negative relationship was found in MCPA treatments.