Impact of Nealley's Sprangletop on Rough Rice Yield

Two field studies were conducted in Louisiana to determine the impact of Nealley's sprangletop on rough rice yield under multiple environments in 2014, 2015, and 2016. The first study evaluated optimal timings of Nealley's sprangletop removal for optimizing rough rice yields. The second study evaluated the impact of Nealley's sprangletop densities on rough rice yield. Nealley's sprangletop was removed with applications of fenoxaprop at 122 g ai ha-1 at 7, 14, 21, 28, 35, and 42 d after emergence (DAE). Nealley's sprangletop removal at 7 and 14 DAE resulted in higher rough rice yields of 7,880 and 6,960 kg ha-1, respectively, when compared with the rice from the season-long Nealley's sprangletop competition with a 6,040 kg ha-1 yield. Delaying herbicide application from 7 DAE to 42 DAE resulted in a yield loss of 1,740 kg ha-1. Over the 35-d delay in application, rough rice yield loss from Nealley's sprangletop interference was equivalent to 50 kg ha-1 d-1. Nealley's sprangletop densities were established at 1, 3, 7, 13, and 26 plants m-2 by transplanting Nealley's sprangletop when rice reached the one- to two-leaf stage. At Nealley's sprangletop densities of 1 to 26 plants m-2, rough rice yields were reduced 10 to 270 kg ha-1, compared with the rice from weed-free plots. Based on regression analysis, Nealley's sprangletop densities of 1, 35, 70, and 450 plants m-2 reduced rough rice yield 0.14%, 5%, 10%, and 50%, respectively. Nomenclature: Fenoxaprop; Nealley's sprangletop, Leptochloa nealleyi Vasey; rice, Oryza sativa L.