| Rice is a major food crop in Jiangxi provice, Sheathed monochoria(Monochoria vaginalis) a troublesome weed to harm the rice growth in paddy fields, bensulfuronmethyl and pyrazosulfuron-ethyl are commonly used herbicides to control Sheathed monochoria in paddy fields. To explore the economic threshold of bensulfuron-methyl and pyrazosulfuron-ethyl on Sheathed monochoria and its application security, based on investigating the occurrence regularity of Sheathed monochoria in double-cropping rice fields in Jiangxi province, the influence of Sheathed monochoria on the growth of double-cropping rice and the economic threshold of bensulfuron-methyl and pyrazosulfuron-ethyl on Sheathed monochoria were studied by transplanting mothed of fixed plant in paddy fields, the susceptibilities of Sheathed monochoria from four areas in Jiangxi provice to bensulfuron-methyl and pyrazosulfuron-ethyl were bioassayed by using pot planting method, and the degradation dynamics of bensulfuron-methyl and pyrazosulfuron-ethyl in paddy soils and rice plants were determined by using high performance liquid chromatography method(HPLC). The results are as follows:1. Sheathed monochoria appeared 10 d after sowing in direct seeding field of the early rice, reached the emergence peak 25 d after sowing, and its density was 29 plant/m2. Sheathed monochoria occurred in transplanting field of the early rice later than that in direct seeding field of the early rice, reached the emergence peak 20 d after sowing, and its density with 26 plant/m2 was lower than that in direct seeding field. Sheathed monochoria appeared 8 d after sowing in direct seeding field of the late rice, reached the emergence peak 15 d after sowing, and its density was 35 plant/m2. Sheathed monochoria occurred in transplanting field of the late rice later than that in direct seeding field of the late rice, reached the emergence peak 20 d after sowing, and its density with 33 plant/m2 was lower than that in direct seeding field.2. Under the interference of Sheathed monochoria, growth characters and grain yield of double-cropping rice decreased gradually with the weed density increased. The power regression model ‘y=axb’ was the best for describing the relationship between Sheathed monochoria density and yield loss [y=6.345x0.528(early rice) and y=6.915x0.532(late rice)]. When bensulfuron-methyl and pyrazosulfuron were used to control Sheathed monochoria in paddy fields, the economic infestation levels of early and late rice were 1.81%~2.02% and 1.33%~1.48%, respectively,and the economic thresholds of early and late rice were 0.09~0.11 plant/m2 and 0.05~0.06 plant/m2, respectively.3. The resistance of Sheathed monochoria against bensulfuron-methyl and pyrazosulfuron-ethyl had already showed difference in paddy fields of Jiangxi Province, of which the resistant levels of the biotypes from Science and Technology Park of Agricultural University in Nanchang city and Xingguo county in Ganzhou city to bensulfuron-methyl were 4.86 and 3.70, respectively, which belonged to decline stage of sensitivity. The resistant levels of the biotypes from Yongxiu county in Jiujiang city and Agricultural Science Research Institute in Jian city to bensulfuron-methyl were 2.95 and 1.75, respectively, which belonged to a sensitive stage. The resistant level of the biotypes from four areas in Jiangxi Province to pyrazosulfuron-ethyl belonged to a sensitive stage.4. The recoveries of bensulfuron-methyl and pyrazosulfuron-ethyl in paddy soils and rice plants were 88.60%~99.16% and 89.86%~99.36% with relative standard deviation(RSD) of 2.66%~10.96% and 1.65%~9.32% at fortified level of 0.05~1.0 mg/kg, respectively. Degradation dynamics of bensulfuron-methyl and pyrazosulfuron-ethyl in paddy soils and rice plants accorded with the first-order kinetics model, of which were Ct =0.3723e-0.0.276 t and Ct =1.0646e-0.6965 t with 2.39 and 0.57 d of half-lives in paddy soils, respectively, Ct =0.4805e-0.2824 t and Ct =2.2234e-0.2742 t with 2.66~1.28 d of half-lives in rice plants, respectively. |
