Research On Practice Code Of Metham-sodium 35% As On Ginseng

Weeds and diseases in the seedling stage are one of the important factors threatening the safe production of ginseng.It will affect the yield and quality of ginseng,the impact on the healthy growth of ginseng is also great.The prevention and control of weeds and diseases in seedling stage is very important.There is a lack of pestcides of ginseng seedling disease,weed and insect control.Metham-sodium is a broad-spectrum fumigating and nematicide,which can treat both soil fungi,underground pests and weeds.It decomposes into MTC in the soil,and it easily spreads in soil and the validity period is longer.It has been widely used in other crops such as Cucurbita pepo L.,Nicotiana tabacum L.,Cucumis sativus L.and other crops,but it has not been reported whether it can be applied to ginseng field.Therefore,in this study,based on the indoor toxicity,a field efficacy trial of metham-sodium on common ginseng diseases and weeds was conducted;A method to detect metham-sodium in the ginseng was established with high performance liquid chromatography（HPLC）.The residual dynamics and final residue on ginseng were clarified,and finally developed a practice code of metham-sodium 35%AS on ginseng.Results are as following:1.Mycelial growth rate method was used to determine the toxicity of metham-sodium on pathogens of common diseases of ginseng.The results showed that metham-sodium had a good inhibitory effect on each pathogen.EC₅₀0 values of metham-sodium to Fusarium solani,Phytophthora cactorum,Alternaria panax,Botrytis cinerea,Cylindrocarpon destructans,Rhizoctonia solani,Sclerotinia schinseng are 0.555mg/L、0.423mg/L、0.362mg/L、0.697mg/L、0.469mg/L、0.611mg/L、1.04 mg/L,respectivelly.2.Field experiments results showed that the efficacy of metham-sodium 35%AS was from 42.31%to 64.15%at dosages of 30,60 and 90 mL/m² soil fumigation on ginseng seedling disease before sowing of ginseng.The control effect of metham-sodium was 81.85%⁹0.09%,the fresh weight control effect was84.79%⁹5.97%for the annual weeds in the ginseng field including Commelina communis,Chenopodium album,Conyza canadensis,Echinochloa Crusgalli and Polygonum lapathifolium.No negtive effects on the growth of ginseng,no injury occurred.It can increase the seedling emergence rate and seeding rate of ginseng3.A method to detect metham-sodium in the ginseng was established with high performance liquid chromatography（HPLC）.Determined the detection method as:use acetonitrile as the extraction solution;Acetonitrile:Toluene=3:1 as eluent;the solid phase extraction column is ProElut GPR column;Acetonitrile+water is the mobile phase.In this condition,the minimum detectable concentration of metham-sodium was 0.05 mg/kg,the average recovery rate of adding metham-sodium with different mass fractions was from 90.64%to 95.65%,the relative standard deviation is from 2.31%to 5.73%.This method was suitable for the residue quantitative analysis of residue detects of metham-sodium.4.The results of residue dynamic and final residue test showed:the metham-sodium half-life is from 1.8d to 2.0d,the MTC half-life is from 1.3d to 1.9d,which is an easily degradable pesticide.During the harvest period,the final residues of metham-sodium were below 0.05 mg/kg in ginseng soil,fresh and dry root,stem and leaf,respectively,at a dosages of 315000 g a.i./hm²,472500 g a.i./hm² of metham-sodium 35%AS treated with ginseng soil fumigation once 40d before sowing.5.According to residual dynamics and final residue results on ginseng,recommended maximum residue limits（MRLs）of metham-sodium is suggested to be0.05 mg/kg temporarily.Based on the principle of risk assessment,metham-sodium percentage of theory exposed total amount accounting for permitted intake are34.11%less than 100%,it showed that the MRLs of metham-sodium for our country consumer is low risk,and are close to those of CAC and other countries,is helpful to improve the quality and safety of ginseng products in our country and the competitiveness of international trade.It is recommended that the dose is 315000⁴75000 g a.i./hm² of metham-sodium35%AS to control ginseng weeds.Before ginseng sowing,seedbed soil should be fumigated which means soilbeds should be covered for 20 days with plastic film and then deflate for 20 days.