| Rice sheath blight caused by Rhizoctonia solani is one of the three major diseases on rice production.Fungicides such as thifuzamide,azoxystrobin,validamycin,triazolone and carbendazim play an important role in the prevention and control of the disease.However,due to poor application environment(water),high labor cost and aging of rice farmers,it is urgent to develop a simplified pesticide dosage form.Grand Granule(GG)is a new pesticide dosage form developed by Nanjing Gaozheng Agricultural Chemical Co.,Ltd.Therefore,under the condition of the greenhouse,the comparative study of three formulas of 8%thifuzamide and azoxystrobin mixture[grand granule(GG),granules(GR)and wettable powder(WP)]of different dose,spray time and the depth of water on the efficacy of rice sheath blight,safty of the crop,the residue dynamics of two fungicides in rice plants.The main results are as follows:(1)The results of efficacy test showed that when the dosage of 8%thifuzamide-azoxystrobin(GG)reached 350g/667m~2,the control efficacy of the disease strains and the disease indications could reach over 80%and be stable at about 90%,which was significantly higher than the efficacy of GR and WP with the same active ingredients.The average disease strain control efficacy of the treatments of 7 days and 14 days after transplantation were 85.71%and 82.47%,respectively,which were higher than the efficacy of the treatments on the day of transplantation(72.61%)and 28 days after transplantation(78.15%).The average disease indicate control effect of treatment 14 and 28 days after transplantation were 85.71%and 82.47%,respectively.The average disease strain and disease indicate control efficacy were 82.03%and 78.32%with 2 cm water layer,and 77.43%and 77.20%with 4 cm water layer,respectively.All treatments are safe on rice plants.(2)Thifuzamide and azoxystrobin in rice plants were extracted by acetonitrile:water(1:1,v/v),and the extracted solution was purified and detected by LC-MS to obtain:The standard curve of thifuzamide in the range of 0.005 to 2mg/kg was y=17040419.9534x+404503.2673 with a correlation coefficient of 0.9994;The standard curve of azoxystrobin was y=1452825565.9x+1494898.7799,and the correlation coefficient was 0.9999.The average recoveries of thifuzamide were 78.82%,82.00%and91.00%at 0.05,0.5 and 5mg/kg supplemental levels,and the relative deviations were1.08%,4.28%and 7.17%.At the same supplemental level,the average recoveries of azoxystrobin on rice plants were 103.20%,97.89%and 96.20%,and the relative deviations were 4.68,4.62%and 4.83%.The established analytical method was in line with the requirements of pesticide residue detection.(3)The average digestion rates of thifuzamide in the dosage forms of GG,GR and WP on day 7 were 50.66%,57.94%and 64.37%;the average digestion rates at 15 days were71.33%,80.71%and 86.75%.After 30 days,the average digestion rate was more than95%.The mean half-lives of thifuzamide dosage forms of GG,GR and WP were 6.66d,5.26d and 4.58d.The average digestion rates of azoxystrobin in the dosage forms of GG,GR and WP on day 7 were 70.68%,78.47%and 84.23%.The average digestion rates at 15days were 88.92%,89.36%and 97.02%.After 30 days,the average digestion rate was more than 97%.The mean half-lives of pyrimethanil in GG,GR and WP treatments were 5.38d,4.32d and 3.88d. |
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