Productivity, Weed Control and Economics of Transplanted Rice as Influenced by New Post Emergence Herbicide Bispyribac sodium

Field experiments were conducted at

Rice, the most important staple food crop of India is cultivated under various ecosystems of viz., transplanted, direct sown and rainfed situations.To meet the future food requirements of the ever increasing population and to maintain self sufficiency, the estimated rice production in India should be 350 million tonnes by 2020 A.D. In transplanted rice, weed infestations not only reduce the grain yield up to 45 per cent, but also impair the quality of grain.The share of weed management cost is higher than other operations in transplanted rice.Though many pre emergence herbicides are available for controlling weeds, the need for post emergence herbicide is often realized to combat the weeds emerged during later stages of crop growth.More over, due to increasing problem of labour availability for rice cultivation, use of new post emergence herbicide will have greater potential for effective weed management and higher yield.In this context, the present study was carried out to standardize the Bisbyribac sodium, a new herbicide its dose and efficiency in transplanted rice.

Materials and Methods
Field experiments were conducted at Agricultural College and Research Institute, Tamil Nadu Agricultural University, Madurai to evaluate the new herbicide Bispyribac sodium on the growth, yield and weed control efficiency in transplanted rice during Kharif 2011 and 2012.A total of seven treatments were evaluated in a Randomized Block Design and replicated four times.The treatments consisted of T1 -Pre-emergence application of Butachlor @1500 g a.i.ha-1 at 3 days after transplanting (DAT), post emergence application of Bispyribac -sodium 10 SC at 25 (T2), 35 (T3), 50 (T4) g a.i.ha -1 at 20 DAT , T5weed free, T6 -Two hand weedings and T7 -Un weeded check.The soil of the experimental field was clay loam with a pH of 6.8 with NPK status of low, medium and high, respectively.The rice varieties ASD 16 and ADT 37 were used during 2011 and 2012 respectively with a spacing of 20 x10 cm.Bispyribac sodium (Nominee Gold 10 % SC) was applied as foliar spray on 20 DAT in the respective treatments as per schedule, while Butachlor was applied as broadcasting with sand mixing.Hand weeding was carried out on 20 and 40 DAT as a separate treatment and for weed free plot, hand weeding was done as and when required.The data on weed density and dry weight were recorded at 45 DAT.The weed dry weight was expressed as kg ha-1.Weed controlling efficiency and weed index were computed.The yield attributes and grain yield of rice were recorded and economics worked out.

Total weed density
The total density of weeds decreased with increase in doses of Bispyribac sodium, but not significantly (Table1).The lowest total weed density was observed under weed free plots.However, this was statistically similar with application of all the doses of Bispyribac sodium during both the years of experimentation.The total weed density under the treatments Butachlor application at 1500 g a.i.ha-1 and hand weeding twice were similar and significantly higher than all the doses of Bispyribac sodium.The highest weed density was observed in unweeded control plot.Reduction in weed density due to the application of Bispyribac sodium at 15 and 25 DAT in transplanted rice was reported by Yadav et al. (2009).Similar effective control of grasses, sedges and BLW in rice fields was documented by Schmidt et al. (1999).The present results are also in conformity with the findings of Kumaran et al. (2012), who registered lower weed density under Bispyribac sodium than other weed management treatments in direct seeded rice.

Total weed dry weight
Application of Bispyribac sodium at all the doses resulted in significant reduction in total weed dry weight than Butachlor application, twice hand weeding and unweeded check (Table 1).However, the total weed dry weight under the higher dose of Bispyribac sodium at 50 g a.i.ha-1 was on par with lower doses of 25 and 35 g a.i.ha-1 indicating the sufficiency of lower dose of 25 g a.i.ha-1 for effective weed management in transplanted rice in both the years of study.The weed controlling effect of pre emergence application of Butachlor and two hand weeding was lesser than Bispyribac sodium as evident from significantly higher weed dry weight under above two treatments.The highest weed dry weight of was registered in unweeded control plot.
Post emergence application of Bispyribac sodium at 15 or 25 DAT significantly decreased the weed dry weight in transplanted rice (Yadav et al. 2009).Similar results of lower weed dry weight with the application of Bispyribac sodium at 40 g a.i.ha-1 than Butachlor and Anilophos in transplanted rice was reported by Nalini et al. (2012).The significant reduction of weed dry weight by Bispyribac sodium at 30 g a.i.ha-1 than pre emergence herbicide application in dry seeded rice was also observed by Walia et al., (2008).

Weed control efficiency and weed index
Among the weed control treatments, application of Bispyribac sodium at 50 g a.i.ha-1 recorded the highest weed control efficiency of 98.1 and 98.5 per cent during 2011 and 2012 respectively (Table 1), which was followed by the same herbicide with lower doses of 35 g a.i.ha-1 (97.5 and 97.8 per cent) and 25 g a.i.ha-1 (96.5 and 97.1 per cent).The weed  Yun et al. (2005).Higher weed control efficiency with Bispyribac sodium application in both transplanted rice and direct seeded rice ,reported by Nalini et al. (2012) is also in favour of the present study.

Yield attributes of rice
All the yield attributes of rice were significantly influenced by the weed management practices (Table 2).Higher number of panicles m-2 of 420 and 312 during 2012 and 2011 respectively, were recorded by weed free plot, which was on par with that of all the doses of Bispyribac sodium application in both the years of study.Application of Bispyribac sodium at 25 g a.i.ha-1 though registerd numerically lower number of panicles m-2, its effect on producing tillers was on par with that of higher doses and twice hand weeding and significantly higher than Butachlor application.Regarding panicle length, weed free plot though recorded higher values, it was on par with all the doess of Bispyribac sodium and hand weeding twice.Similarly number of grains panicle -1 were also higher with weed free plot but on par with Bispyribac sodium at 50 g a.i.ha-1.Post emergence application of Bispyribac sodium at 25 g a.i.ha-1 registered 129 and 146 number of grains panicle-1 which was on par with that of Bispyribac sodium at 50 g a.i.ha-1 (139 and 148 ) ; and twice hand weeding (136 and 145 ), and significantly higher than Butachlor application (118 and 125).Similar result of higher yield attributes of transplanted rice under Bispyribac sodium application was reported by Yadav et al. (2009).

Grain yield
Significant variation among the weed management practices was found on the grain yield of rice and higher yield was associated with Bispyribac sodium (Table 2).Weed free plot registered the highest grain yield of 7139 kg ha-1 6927 kg ha-1 during 2011 and 2012, respectively, which was on par with all the doses of Bispyribac sodium.Post emergence application of Bispyribac sodium at 25 g a.i.ha-1 recorded a grain yield of 6838 kg ha-1 and 6510 -1 during 2011 and 2012, respectively, which was on par with higher doses of Bispyribac sodium and significantly superior than Butachlor application.The effect of all the three doses of Bispyribac sodium on grain yield was significantly higher than Butachlor application and unweeded control.The per cent yield increment due to the application of Bispyribac sodium at the rate of 25 g a.i.ha-1 were 7.9, 2.2 and 73.5 during 2011 and 0.8, 9.4 and 95.7 per cent during 2012 than tiwce hand weeding, Butachlor application and unweeded control, respectively.There was a severe yield loss due to weed infestation as evident from 44.78 and 51.28 per cent yield reduction, respectively during the above years of study under unweeded plot over weed free plot.The higher grain yield in Bispyribac sodium applied plots was attributed to lesser weed population and weed dry weight which might have caused lesser weed competition with rice resulting in the production of higher yield attributes, which in turn reflected in higher yield.The favourable reports of effective weed control along with higher grain yield by Bispyribac sodium against mixed weed flora in transplanted rice (Yadav et al., 2009), wet seeded rice (Yadav et al 2007) and dry seeded rice (Walia et al., 2008) are in confirmation with the present investigation.Murali Arthanari et al. (2012) obtained similar grain yield of transplanted rice under Bispyribac sodium at both the doses of 50 and 35 g a.i.ha-1 .

Economics
The economic analysis of weed management practices (Table .2) revealed that higher economic benefits were realized under lower doses of Bispyribac sodium application.Post emergence application of Bispyribac sodium at 25 g a.i.ha-1 registered the highest net profit of Rs. 42,452 ha-1 and Rs.40,400 ha-1 during 2011 and 2012 respectively followed by Bispyribac sodium at 50 g a.i.ha-1 (Rs.42,086 ha-1 and Rs.40, 330 ha-1).Higher benefit-cost ratio was also associated with Bispyribac sodium at 25g a.i.ha-1 (2.89 and 2.61), which was followed by Bispyribac sodium at 35g a.i.ha-1 (2.81 and 2.54).Though higher dose of Bispyribac sodium at 50 g a.i.ha-1 recorded slightly higher grain yield, economically it is inferior to that of its lower dose of 25g a.i.ha-1.
Thus it may be concluded from the study that application of post-emergence herbicide Bispyribac sodium at the rate of 25 g a.i ha-1 on 20 DAT could be a suitable and economical herbicidal weed management practice for transplanted rice for higher productivity.