Estimation of critical competition period of red sprangletop (Leptochloa chinensis L.) in direct-seeded fine grain rice (Oryza sativa L.)

Abstract

Red sprangletop (Leptochloa chinensis L.) has become one of the most troublesome weeds for direct-seeded rice (DSR). The degree of cost-effectiveness of any weed control strategy against this weed needs accurate information about its critical timing of weed removal (CTWR) in DSR production system. A two-year field study was executed to estimate yield losses and critical period of competition of red sprangletop weed in the fine-grain DSR. Experimental treatments were crop-weed competition periods of 7, 8, 9, 10 weeks after emergence (WAE) of rice crop. A full season weed free and weed infested plots were also kept as controls for comparison purpose. Results exhibited that during both years, each successive prolongation in weed competition period significantly increased red sprangletop dry weight and its N, P and K uptake causing significant reduction in yield attributes and paddy yield. Consequently, during years 2018 and 2019, the highest values of weed dry weight (1168 and 1452 kg ha(-1), respectively) and N, P and K uptakes (33.5 and 41.7, 7.67 and 9.62, 31.1 and 42.3 kg ha(-1), respectively) were recorded with full season red sprangletop competition. In comparison to weed free control, this treatment resulted in the highest reduction in plant height (30-49%), panicle length (23-45%), tillers m(-2) (66-78%), grains panicle(-1) (42-61%), 1000-grain weight (31-24%), paddy yield (65-75%) and biological yield (67-70%). The logistic model estimated the CTWR of red sprangletop in DSR to be initial 33-49 DAE and 31-52 DAE in order to prevent 10% yield losses during years 2018 and 2019, respectively.