www.banglajol.info/index.php/JSF 39 Journal of Science Foundation, July 2014, Vol. 12, No.2 pISSN 1728-7855 Original Article Effect of Herbicide Dose and Water Management on Weed Control Efficiency and Yield Performance of Boro Rice Md. Ranju Ahmed 1 , Md. Nasimul Bari 2 , M. Moynul Haque 3 , G.K.M. Mustafizur Rahman 4 Abstract An experiment was conducted at the Experimental Farm of the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Salna, Gazipur during November 2011 to May 2012 to determine the effect of pre-emergence herbicide Pretilachlor @ 75%, 100%, 125%, 150%, 175% and 200% of the recommended dose under two water management regime i.e. continuous flooding and field capacity on weed suppression and yield performance of Boro rice cv. BRRIdhan28. One weed free and one control (unweeded) treatment were also imposed for treatment comparison. The experiment was laid down in Split Plot design with three replications. Standard management practices for transplanted rice were followed. Continuous flooding was found to contribute better weed control efficiency than field capacity. At 60 DAT, the highest weed control efficiency of 65.75% was found in the treatment receiving Pretilachlor @ 125% of the recommended dose under continuous flooding and the least (54.76%) was found in the treatment receiving 75% of the recommended dose under field capacity. Continuous flooding contributed to more tillers than field capacity, and herbicide up to 125% of the recommended dose enhanced tillering in rice. At 75DAT the highest number of tillers (17.53 hill -1 ) were found in the plots receiving Pretilachlor @ 125% of the recommended dose under good water management (W1T3), while the lowest (11.10 hill -1 ) was recorded in W2T6 treatment receiving Pretilachlor @ 200% of the recommended dose under field capacity. The highest tiller mortality (27.90%) was observed in W1T3 treatment, whereas the least (8.06%) was observed in W2T5 treatment receiving the same herbicide @175% of the recommended dose under field capacity. Application of Pretilachlor at recommended dose under continuous flooding contributed to the highest crop dry matter production (1144.60g m -2 ) thus leading to the highest grain yield of 6.31 t ha -1 being followed by the treatment receiving Pretilachlor @ 125% of the recommended dose under same water management yielding 5.95 t ha -1 along with the highest harvest index of 0.58. Results revealed that Pretilachlor at recommended dose might be considered as viable option for weed management in transplanted Boro rice cultivation for effective weed management and satisfactory grain yield provided that appropriate water management is adopted. [Journal of Science Foundation 2014;12(2):39-46] Keywords: Rice; herbicide dose; water management; weed control; grain yield Introduction Rice is the staple food in Bangladesh. The area and production of rice in 2006 were 10.58 million hectares and 27.32 million metric tons respectively (BBS, 2007) in Bangladesh. Weeds is the most important constraint in rice crop and weed management is one the most time consuming and laborious practice in rice cultivation. Poor weed control is one of the major factors for yield reduction of rice depending on the type of weed flora and their intensity (Amarjit et al., 1994). Mamun (1990) reported that weed growth reduced grain yield by 69-100% for direct seeded aus rice, 16-48% for aman rice and 22-36% for modern Boro rice. 1 Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh 2 Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh 3 Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh 4 Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh Correspondence: Md. Nasimul Bari, Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh; Email: bari_nasimul@yahoo.com