Studies On The Control Of Seedling Diseases And Residual Dynamics Of Metalaxyl-M And Hymexazol 30% As In Ginseng

Problems of pesticide residue in ginseng products have caused widespread concern in the world. The main reasons resulting in ginseng pesticide residue exceeding are the irrational application of pesticides, scientific and rational application of the pesticides are the key technical measures to reduce pesticide residues in ginseng. Metalaxyl-M·hymexazol 30% AS is an effective soil treatment fungicide for controlling crop seedling diseases, but the standard application techique on ginseng disease control has not been decided.In this study, indoor toxicities of metalaxyl-M·hymexazol against main pathogens causing ginseng seedling diseases, field efficacy trials, residual detection method and law of residual degradation have been carried out so that provide scientific basis to establish criterion of scientific application, to regulate its application and reduce the residues in ginseng, so as to ensure the ginseng production safety and green and sustainable development of ginseng industry. The main results as follows:1. The indoor toxicities of metalaxyl-M·hymexazol and its different proportions against Rhizoctonia solani and Fusarium solani causing ginseng seedling blight and root rot were determined. Of the four ratios(1:5, 2:4, 3:3, 3.5:2.5) of mefenoxam:hymexazol, the ratio of 1:5 have the best inhibitory effect with more than 120 of CO coefficient toxicity and is of synergistic effect, and CO toxicity coefficient of other three ratios were all less than 90 and be of antagonism effect.2. According to the pesticide guidelines for the field efficacy trials, under field conditions, control effect of metalaxyl-M·hymexazol 30% AS for ginseng seedling blight and root rot disease were tested in Ji’an city and Fusong country. The results of 2 years 2 sites showed that control effects of the fungicide against ginseng seedling blight and Fusarium root rot were 68.51%~82.24% and 68.39%~79.27%, respectively at the dose of 1.35~2.7 g/m2 and soil treatment, and have a better control effect than the control single fungicide and other fungicide. The germination rates and left seedling rates of ginseng were also better than those of the control single and other fungicide.3. The detection method of metalaxyl-M and hymexazol in ginseng with high performance liquid chromatography tandem mass spectrometry(LC-MS/MS) are established. Based on external standard method, the detection conditions are set as follows: N-propylethylenediamine solid-phase extraction column(PSA), with 0.1% formic acetonitrile-water as mobile phase and gradient elution. 5 mins are used as the extraction time, acetonitrile is used as the extraction solvent, and acetonitrile-toluene(3:1, by vol) is used as the extraction solvent volume. Under the optimized chromatography and mass spectra conditions, the detection limit of metalaxyl-M and hymexazol is 0.01 mg/kg. The precision accuracy of metalaxyl-M is 3.47%~8.15%, average recoveries are 93.38~104.92%.The precision accuracy ofhymexazol is 2.37%~9.75%, average recoveries are 85.15%~104.65%. This detection method is satisfied to the requirements of residue and is suitable for metalaxyl-M and hymexazol residue determination in ginseng.4. Results of residue dynamics and the final residues in 2 years and 2 sites showed that the half-lifes of metalaxyl-M and hymexazol are 10.8~13.6 d and 6.3~8.2 d, respectively, and two fungicides are all more easily degradable pesticide. Final residues of metalaxyl-M in fresh ginseng and dry ginseng root, soil, and stem and leaf after 135 day application were all lower than 0.01 mg/kg, final residues of hymexazol were lower than 0.01 mg/kg after 80 day application in fresh ginseng and stem of ginseng root, stem leaf and soil.5. According to the results of residue degradation and toxicological evaluation, the maximum residue limits(MRLs) of the metalaxyl-M and hymexazol are determined temperately as 0.1 mg/kg. Application criterion of metalaxyl-M and hymexazol 30% AS are as follows: soil treatement one time at the dosages of 2 g/m2 at ginseng seed sowing, the safe interval is 135 days.