Pre-plant and pre-emergence herbicides for weed management in transplanted rice
The study on pre-plant and pre-emergence herbicide weed management in transplanted rice during Rabi 2011–12 at Tamil Nadu Agricultural University, Coimbatore revealed that pre-plant application of glyphosate 0.75 kg a.i. ha−1 recorded higher mean grain yield (5766 kg ha−1), lower weed density (3.2, 6.7 and 5.6 m−2 at 20, 40 and 60 DAT), dry weight (2.0, 3.7 and 4.1 g m−2 at 20, 40 and 60 DAT) and weed control efficiency (71, 5, 69.5 and 69.2% at 20, 40 and 60 DAT) compared to non application of glyphosate. The application of pre-plant glyphosate eliminated most existing vegetation and prevented weed establishment. In main field among the different treatments early post emergence (EPOE) application of Bensulfuron methyl+ pretilachloar (6.6 GR) at 0.06+0.60 kg/ha recorded significantly higher grain yield (6450 kg ha−1), straw yield (8614 kg ha−1) through better weed control efficiency as indicated by lower weed density (4.3, 5.5 and 4.6 m−2 at 20, 40 and 60 DAT), reduced weed dry matter (2.2, 3.4 and 3.0 g m−2 at 20, 40 and 60 DAT) and higher weed control efficiency (80.6, 83.2 and 85.0% at 20, 40 and 60 DAT) followed by PE application of Pretilachlor at 0.75 a.i. Kg ha−1 + HW at 40 DAT other treatments. This is due to better control of pre emerged weeds and as well as emerging weeds as it has a high level of activity against broad leaved weeds and sedges. Pre-plant application of glyphosate 0.75 kg a.i ha−1 recorded highest net return (25, 188/ha) compared to non glyphosate application (/ha 22, 579). Among the different herbicides, EPOE Bensulfuron methyl + pretilachlor (6.6 GR) at 10 DAT registered higher gross returns (/ha. 59, 318 ha−1), net return (/ha. 33, 120 ha−1) and B: C ratio (2.19).