| Red sprangletop(Leptochloa chinensis (L.) Nees.) is a troublesome weed seriously damaging rice growth and reducing rice yield in direct-seeding rice fields. Cyhalofop-butyl is an herbicide which is commonly used to control weeds such as red sprangletop in paddy fields. The effects of red sprangletop on rice growth in direct-seeding rice fields and its economic threshold were investigated by adding series experiment under different density of red sprangletop. The germination characteristic of red sprangletop seed and its sensibility to cyhalofop-butyl was assayed by indoor culturing method. The degradation dynamics of cyhalofop-butyl in paddy soil and rice plant were investigated by HPLC. The results are as follows.(1) The plant height, tillers, effective spikes, filled grains per panicle,1000-grain weight and grain yield of direct-seeding rice decreased gradually with the interference of red sprangletop as the weed density increased. For yield levels of 7500 kg·hm-2(early rice), 9750 kg·hm-2 (middle rice) and 8 625 kg·hm-2 (late rice), the economic infestation levels for manual weeding were 12.73%,8.80% and 10.07%, respectively, and the red sprangletop economic thresholds were 2.26,3.52 and 3.56 plant/m2, respectively. Also for yield levels of 7 500 kg·hm-2 (early rice),9 750 kg·hm-2 (middle rice) and 8 625 kg·hm-2 (late rice), the economic infestation levels for application of 10% cyhalofop-butyl EC or 30% oxaziclomefone SC were 2.26%-2.72%,1.56%-1.88% and 1.77%-2.12%, respectively, and the L. chinensis economic thresholds were 0.06-0.09,0.59-0.72 and 0.25-0.32 plant/m2, respectively. The inhibitory effects of red sprangletop on rice were positively correlated with its density, which there were differences among early, middle and late rice. Also the economic thresholds of chemical control on red sprangletop showed early rice<late rice<middle rice based on the analysis of control economic thresholds.(2) The sensitivity of eight red sprangletop biotypes from paddy fields in Jiangxi Province to cyhalofop-butyl was determined using pot planting method. Results showed that the arrangement order of the resistance of red sprangletop biotypes from different areas to cyhalofop-butyl was Wenzhen town of Jinxian country>Zhu Guang farms> Honghu farms> Qingtang town of Ningdu county> Agricultural Research Institutes of Ganzhou city>Chian town of Fengxin county> Agricultural Research Institutes of Ji’an city>Guangfu town of Nanchang county. The resistant level of the biotype was low from Wenzhen town of Jinxian country, and in the sensitivity decline stage from Zhu Guang farms and Honghu farms, and in a stage of sensitivity to cyhalofop-butyl from Qingtang town of Ningdu county, Agricultural Research Institutes of Ganzhou city, Chian town of Fengxin county, Agricultural Research Institutes of Ji’an city and Guangfu town of Nanchang county.(3) To evaluate the safety of cyhalofop-butyl in paddy soil and rice plant, and established its application standard in paddy field, field experiment was conducted in Nanchang City in 2014 to investigate the degradation dynamics of cyhalofop-butyl in paddy soil and rice plant. The high performance liquid chromatography method for the determination of cyhalofop-butyl residues in paddy soil and rice plant was developed. The recoveries of cyhalofop-butyl in paddy soil and rice plant were 85.97%-93.38% and 85.10%-88.19% with relative standard deviation (RSD) of 3.61%-5.37% and 2.23%-7.00% at fortified level of 0.1-1 mg·kg-1, respectively. The degradation dynamics of cyhalofop-butyl accorded with C=5.21e-0.378t in paddy soil and C=3.871e-0-523t in rice plants. The half-lives were 1.83 d and 1.33 d in paddy soil and rice plant, respectively. This showed that cyhalofop-butyl could be rapidly degraded, so it was safety to rice and paddy field. |
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