2014 Volume 17 Issue 4 Pages 315-320
Wet-seeded rice is a common method of sowing in Vietnam. Weeds, including weedy rice, however, are a major problem in this establishment method. A study was conducted in a farmer's field to evaluate the effect of pretilachlor dose (0, 300, 600, and 900 g ai ha–1) on the management of weedy rice and other weeds in wet-seeded rice cultivation in the spring-summer, summer-autumn, and winter-spring seasons of 2012-13. The herbicide was applied 1 day after sowing. Weeds belonging to the grass, broadleaf, and sedge groups were effectively controlled by the lowest herbicide dose (300 g ha–1). Overall, weed control did not increase with increases in herbicide dose after 300 g ha–1, suggesting the optimum dose for pretilachlor in wet-seeded systems. The application of pretilachlor at 300 g ha–1 significantly reduced the number of weedy rice panicles (20–69%) and weedy rice biomass (15–26%). The highest pretilachlor dose (i.e., 900 g ha–1), however, was better than the lower doses in reducing the number of weedy rice panicles (47–80%) and weedy rice biomass (41–54%). The non-treated plots produced a rice grain yield of 210, 2000, and 1850 kg ha–1 in the spring-summer, summer-autumn, and winter-spring seasons, respectively. Compared with the non-treated plots, the lowest dose of pretilachlor improved grain yield. However, maximum yield was obtained by applying the highest dose of pretilachlor; 2690, 4490, and 5150 kg ha–1 in the spring-summer, summer-autumn, and winter-spring seasons, respectively. The results of our study suggest that a broad spectrum of weed flora can be easily managed by a lower dosage of pretilachlor in wet-seeded rice; however, the herbicide dose needs to be increased to 900 g ha–1 in order to decrease the weedy rice problem.
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