Evaluation of New Herbicide (Bispyribac sodium 10 SC) on Weed Control and Yield in Direct Seeded Lowland Rice ( Oryza sativa )

Field investigation was carried out to evaluate the new formulation of bispyribac sodium 10 SC in direct seeded rice during rabi (August to February ) of 2011-12 at Tamil Nadu Agricultural University, Coimbatore. The experiment was laid out in a randomized block design and replicated thrice with the objective to find out the effect of bispyribac sodium 10% SC on weed control efficiency and yield of direct seeded rice. The treatments consist of EPOE application of bispyribac sodium 10% SC at 10, 20, 40 g ha -1 , nominee gold 20 g ha -1 (bispyribac sodium 10 SC) on 15 DAS and PE butachlor 1.5 kg ha -1 , anilophos 0.45 kg ha -1 , pretilachlor S 0.45 kg ha -1 on 3 DAS + HW on 40 DAS and power weeder, conoweeder weeding at 20 and 40 DAS, HW twice on 20 and 40 DAS and unweeded control. Application of pretilachlor S 0.45 kg ha -1 on 3 DAS + HW on 40 DAS registered lower weed density and dry weight at 20 DAS but during the later stages of crop growth EPOE application of bispyribac sodium 10% SC 40 g ha -1 recorded lower weed density and dry weight. The grain and straw yield in both the treatments were comparatively higher than other treatments.

Rice commands recognition, as a supreme commodity to mankind, because rice is truly life, culture, a tradition and a means of livelihood to millions. Rice is the staple food for about 50 per cent of the world's population that resides in Asia, where 90 per cent of the world's rice is grown and consumed. In Asia, India has the largest area under rice (41.66 million hectare) accounting for 29.4 per cent of the global rice area. Rice is grown in an area of 45 million ha annually with a production of 80.14 million tonnes, with an average productivity of 2177 kg ha-1 during 2009 to 2010 (FAO, 2010). India has to produce 135-145 million tonnes of rice by 2020 to feed the additional 350 million people (Prakash et al., 2008).To sustain present food self-sufficiency and to meet future food requirements, India has to increase its rice productivity by 3 per cent per annum.
Direct seeding is practiced in areas of uncertain distribution of rainfall or inadequate availability of irrigation facilities. Direct seeded rice is gaining momentum in India due to high demand of labour during peak season of transplanting and short period of availability of water. The weed competition is more severe in direct seeded rice as crop and weeds emerge simultaneously. The yield loss due to weeds varies from 40 to 100 per cent in direct seeded rice (Choubey et al ., 2001). Timely weed control is crucial to increase the productivity of rice. Chemical weed control offers economic and efficient weed control if applied at proper time with correct dose and stage (Kumar and Sharma, 2005). The herbicides presently used in rice are mainly preemergence and weeds coming at later stages of crop growth are not controlled as effectively as at emergence stage. This situation warranted for initiating research efforts to evaluate and identify suitable post emergence herbicide(s). Use of alternative herbicides that provide wide-spectrum of weed control would be desirable for effective weed control. One of the most important classes of herbicides that have been used popularly all over the world is sulfonylurea group of herbicides. Among several sulfonylurea herbicides, bispyribac sodium is a new post emergence rice herbicide. It has eminent activity against a broad spectrum of annual and perennial rice weeds. Therefore, the present study was undertaken to evaluate the performance of new post-emergence herbicides, against complex weed flora in low land direct seeded rice system.

Material and Methods
Field experiment was conducted at Tamil Nadu Agricultural University, Coimbatore during rabi (August to February) of 2011-12. The experiment was laid out in a randomized block design with three replications. The soil fertility status was medium in available nitrogen (234 kg ha-1), low in available phosphorus (16.2 kg ha-1) and high in available *Corresponding author email : kumaran.agri@gmail.com potassium (467 kg ha-1). Medium duration rice variety CO (R) 48 was used as a test variety in the study. The treatments consisted of early post emergence application of bispyribac sodium 10% SC at 10, 20, 40 g ha-1, nominee gold (bispyribac sodium 10% SC) 20 g ha-1 on 15 days after sowing and PE application of butachlor 1.5 kg ha-1, anilophos 0.45 kg ha-1, pretilachlor S 0.45 kg ha-1 on 3 days after sowing + HW on 40 days after sowing and power weeder, conoweeder weeding at 20 and 40 days after sowing, HW twice on 20 and 40 days after sowing and unweeded control. A seed rate of 30 kg ha-1 was adopted. The sprouted seeds were uniformly sown by manually operated rice drum seeder developed by TNAU, Coimbatore, which drops the seeds at 20 cm apart in continuous row. Careful water management practices were adopted in the first one week.
Recommended doses of fertilizer of 150:50:50 kg N, P2O5, K2O ha -1 was adopted. The entire quantity of P was applied as basal. Nitrogen in the form of urea and potassium as muriate of potash were applied in four equal splits at basal, active tillering, panicle initiation and at flowering stages. The farm yard manure was applied @ 12.5 t ha-1 at last ploughing, incorporated and then leveled. The quantity of early post emergence (EPOE) and pre emergence (PE) herbicides were calculated as per the treatmental schedule. The pre emergence (PE) herbicide was applied using fan type nozzle (WFN 40) 3 days after sowing while the new molecular bispyribac sodium 10% SC, nominee gold were applied as early post emergence herbicides on 12 days after sowing. The herbicides were applied by keeping a thin film of water in the field. The field was neither drained nor irrigated for 2 days after application of herbicides. Hand weeding 53 was given for PE herbicides treated plots 40 days after sowing. The unweeded control plots were kept undisturbed for the entire cropping period.

Total weed density
Significant variation in total weed density was observed among the weed control treatments (Fig 1). At early stage of crop growth, lesser weed density was observed in the weed free plot. Statistically it was on par with the application of pre-emergence herbicide pretilachlor S at 0.45 kg a.i ha-1 + HW on 40 DAS, butachlor 50% EW at 1.5 kg a.i. ha-1 + HW on 40 DAS and anilophos 30% EC at 0.45 kg a.i. ha-1 + HW

Fig.1. Effect of weed management practices on total density of weeds
on 40 DAS. On 40 and 60 DAS, the total weed density was found to be lesser in weed free treatment and it was on par with application of bispyribac sodium 10% SC at 40 g and pretilachlor S at 0.45 kg a.i ha-1 followed by one hand weeding on 40 DAS (T7).

Total weeds Dry Matter Production
Significant variations were observed on total weed DMP on 20, 40 and 60 DAS due to the adoption of weed management practices (Table 1)

Grain yield
Since, different weed management practices did exert significant influence on growth and yield attributes of rice crop, it reflected on grain yield also( Table 2). As in the weed control efficiency, significantly higher grain yield was recorded by weed free check (5268 kg ha-1). It was 135.26 per cent higher than weedy check and 13.15 per cent higher than hand weeding twice on 20 and 40 DAS (farmer's method), which recorded 4655 kg ha-1. Among the weed management treatments, EPOE bispyribac sodium 10% SC at 40 g ha-1 (T3) recorded 5058 kg ha-1 grain yield and was on par with pretilachlor S at 0.45 kg a.i ha-1 as preemergence + one hand weeding on 40 DAS (T7) which recorded 5005 kg ha-1. Earlier treatment has registered 8.65 per cent and later registered 7.51 per cent higher grain yield over hand weeding twice on 20 and 40 DAS (T10).
Butachlor 50% EW + one hand weeding on 40 DAS (T5) and anilophos 30% EC +one hand weeding on 40 DAS (T6) recorded the grain yield with 0.01 and 0.49 per cent lesser than hand weeding twice on 20 and 40 DAS (T10), where as the mechanical weed control method with power weeder (4218 kg ha-1) and manually operated cono weeder (4221 kg ha-1) recorded 9.37 and 9.31 per cent lesser grain yields than hand weeding twice on 20 and 40 DAS. But, they have recorded significantly higher yield than weedy check.

Straw yield
Similar to grain yield, straw yield was also influenced significantly by different weed management practices (Table 2). Weed free check recorded the highest straw yield of 8900 kg ha-1, which was on par with integraded weed management method of pre-emergence application of pretilachlor at 0.45 kg a.i. ha-1 + HW at 40 DAS (8600 kg ha-1 ) and early post-emergence herbicide application of bispyribac sodium 10% SC at 40 g ha-1 (8520 kg ha-1). Unweeded check recorded significantly low straw yield of 4389 kg ha-1.

Harvest index
Different weed management practices failed to reach the level of significance in influencing the  (Table 2). However, the maximum harvest index of 0.59 was recorded by early postemergence herbicide application of bispyribac sodium 10% SC at 40 g ha-1(T 3), pre-emergence application of butachlor at 1.5 kg a.i. ha-1 + HW at 40 DAS (T5), anilophos at 0.45kg a.i./ha-1 + HW on 40 DAS (T6), hand weeding on 20 and 40 DAS and weed free check (T11).

Economics of weed management practices
Adoption of different weed management practices significantly influenced the gross returns, net returns and B:C ratio (Table 3a, 3b). The treatment consisting of application of bispyribac sodium 10% SC at 40 g ha-1 registered Rs. 60,698 ha-1 as gross income next to weed free check Rs. 63,217 ha-1 with a net return of Rs. 38,970 ha-1 and a B:C ratio 2.79. This was followed by pretilachlor at 0.45 kg a.i. ha-1 + HW on 40 DAS with a gross return of Rs. 60,064 ha-1, net return Rs. 36,171 ha-1 and B:C ratio 2.51.

Conclusion
The results of this experiment revealed that among the weed management practices, application of early post emergence herbicide bispyribac sodium 10 SC 40 g ha-1 (T3) recorded lesser weed density and helped to enhance crop growth, yield components and yield in direct seeded rice. Hence, bispyribac sodium 10 SC at 40 g a.i. ha-1 as early post emergence herbicide is found to be an effective and alternative post emergence herbicide for better weed control, higher grain yield and economic returns in direct seeded lowland rice.