Effect of different herbicide molecules on weed control in transplanted rice ( Oryza sativa L . )

A field experiment was conducted during kharif season of 2012 with carried out in RBD with three replications, having 12 number of treatments viz. Bispyribac-Na 25 g, Pretilachlor 1000 g, Penoxsulam 22.5 g, Pyrazosulfuron 20 g, Bispyribac-Na + ethoxysulfuron methyl 25 g + 18.75 g, BispyribacNa + almix 25 g + 4 g, Pretilachlor fb ethoxysulfuron methyl 750 g / 18.75g , Pretilachlor fb almix 750 g / 4 g, Pyrazosulfuron fb MW 20 g / 25 DAT, Londex 10 kgha along with weed free and weedy check. The density of BLWs, narrow leaved weeds and sedges as well as the total weed density and dry weight were recorded significantly less with Bispyribac-Na + almix 25 g + 4 g ha as compared to rest of the treatments. Yield attributes viz. panicle length, test weight as well as grain and straw yield were significantly higher in Bispyribac-Na + almix 25 g + 4 g ha followed by Pretilachlor fb almix 750 g / 4 g, Bispyribac-Na + ethoxysulfuron methyl 25 g + 18.75 g and Pretilachlor fb ethoxysulfuron methyl 750 g / 18.75 g ha. Key word: Weeds, Rice, Herbicides, Growth, Yield Introduction Rice (Oryza sativa L.) is primary staple food of more than 60 per cent of the world population that is why the rice production always holds a key role in the overall food situation of the whole world. Fortunately, India ranks first in acreage (44.3 million hectares) and second in production (99.15 million tonnes) after China. Rice is the staple food for three fourth of the Indian population alone contributes about 43% of food grain and 46% of cereal production in the country. In 2009-10 about 64% of total rice area is situated in eastern part of country covering Uttar Pradesh, Bihar, West Bengal, Assam, Orissa and Madhya Pradesh. The area, production and average productivity of rice in India were 44.3 million hectare, 99.15 million tonnes and 2235 kg ha, respectively, in 2009-10 (Anonymous, 2010). A number of factors are responsible for low productivity of rice in U.P., especially in the eastern part of Uttar Pradesh. Among them, invasion of weeds is one of the very serious factors, affecting the crop yield adversely (De Dutta, 1986). It has been reported by Gogoi (1995), that losses due to weeds in rice recorded in the range of 20-95%. The most of weed flora in rice is C 4 type, which is aggressive and strong competitor of rice for various growth factors. On an average, uncontrolled weed growth in transplanted rice causes the yield losses from 15 to 45%, depending upon type of weed flora and their intensity along with soil and climatic conditions (Gautam and Mishra, 19960). Some grassy weed like Echinochloa colona and E. crus-galli resemble rice plant during intial stages and therefore escape manual removal, the costly and laborious nature of manual weeding has made chemical weed control popular among rice farmers. Herbicides provide the weed control at initial stages thereby providing crop an advantage of good growth from beginning, thereby providing competitive edge over the later emerging weeds. For the past many years, butachlor and anilofos are being used for weed control in rice. Past experiences are being used for weed control that the continouous use of one herbicide led to development of resistance problem. Thus, the present a number of high potency herbicide molecules have been developed which are applied at a substantially lower doses. Likewise, sequential application of herbicide molecules is also required to control the wide spectrum of weed flora in the rice. The objectives of study are: (1) To find out the effect of different herbicide molecules on growth and yield of transplanted rice and associated weeds. (2) To find out the spectrum of weed flora in transplanted rice. Materials and Methods A field experiment was conducted at agronomy research farm of NDUAT, Faizabad during kharif season of 2012 with an objective to find out the effect of different herbicide molecules on growth and yield of transplanted rice and associated weeds. The experimental site falls under sub-tropical zone in Indo-gangetic plains having alluvial calcareous soil and lies between 24.4-26.7 North latitude and 82.1283. 98 east longitude with an elevation of about 11.3 meter from mean sea level. The soil of the experimental field was silt loam, having pH 7.82, organic carbon (%) 0.35; available N, P and K values to the tune of 190.55, 13.03 and 254 kg ha, respectively. Field trial was laid out in RBD with three replications, having 12 number of treatments viz. Bispyribac-Na 25 g, Pretilachlor 1000 g, Penoxsulam 22.5 g, Pyrazosulfuron 20 g, Bispyribac-Na + ethoxysulfuron methyl 25 g + 18.75 g, Bispyribac-Na + almix 25 g + 4 g, Pretilachlor fb ethoxysulfuron methyl 750 g / 18.75g , Pretilachlor fb almix 750 g / 4 g, Pyrazosulfuron fb MW 20 g / 25 DAT, Londex 10 kgha along with weed free and weedy check. The herbicide treatments were applied at 2 DAT and 25 DAT as pre & Post emergence to weeds, respectively. But Penoxsulam was applied at 10 DAT with the help of manually operated