Study On The Efficacy Of Pydiflumetofen Against Rice Sheath Blast And Its Environmental Behavior In Paddy Ecosystem

Pydiflumetofen（3-（difluoromethyl）-N-methoxy-1-methyl-N-（1-（2,4,6-trichlorophenyl）propan-2-yl）-1H-pyrazole-4-carboxamide）is a new fungicide developed by Syngenta in recent years.In this paper,based on the evaluation of the efficacy and safety of pydiflumetofen against rice sheath blight,we established a method for the analysis of pydiflumetofen macronutrients and residues,and investigated the dynamics of pydiflumetofen dissipation,final residues and environmental behavior in rice and its environment.The results were as follows:（1）To clarify the inhibitory effect of pydiflumetofen on rice sheath blight,the toxicity of pydiflumetofen was determined indoors using the mycelial growth rate method,and the efficacy of pydiflumetofen was tested outdoors in the field.Toxicity test results:the EC₅₀and EC₉₅ of pydiflumetofen on the growth inhibition of rice sheath blight were 0.4277mg/L and 25.8321 mg/L,respectively;field efficacy test results:In 2019,the control effects of pydiflumetofen for late rice at the application rate of 160-200 g a.i./hm² were62.7%-69.5%and 79%-82%for 7d and 14d,respectively.The control effects for early rice in 2020 were 50.7%-51.4%and 72.6%-74.6%,better than the recommended dosage of tebuconazole 80.625 g a.i./hm².Yield measurement results:when pydiflumetofen is applied160～200 g a.i./hm² in the early stage of rice,the highest yield can be increased by 98.17%.The experiment showed that pydiflumetofen had good inhibitory effect on rice sheath blight and could be used for the control of rice sheath blight,and the best effect was achieved at the application rate of 160-200 g a.i./hm².（2）A method for the analysis of pydiflumetofen in rice field water,soil,plant,brown rice and rice husk was established using high performance liquid chromatography-mass spectrometry（HPLC-MS）.The spiked recoveries ranged from 84.23%to 105.10%with the relative standard deviations（RSDs）between 1.07 and 9.99%for the addition of pydiflumetofen at the concentrations of 0.01,0.05 and 0.1 mg/kg in each matrix of the rice field.The limits of detection（S/N=3）of the method in each matrix were in the range of1.9-3.5μg/kg and the limits of quantification（S/N=10）were in the range of 6.87-12.15μg/kg.The method is simple,rapid,accurate and sensitive,and the results obtained meet the requirements of pydiflumetofen residue detection and are suitable for the determination of pydiflumetofen residues in paddy water,soil,plants,brown rice and rice husk.（3）The results of residual dissipation tests at 4 sites over 2 years showed that the dissipation patterns of pydiflumetofen in field water,soil and rice plants were in accordance with the primary kinetic model.Pydiflumetofen dissipated more rapidly in water than in rice plant samples and soil samples,with half-lives of 0.72-2.47 d,1.07-8.65d and 5.76-14.12 d,respectively.The linear analysis showed that the degradation rate was positively correlated with soil organic matter and p H,and negatively correlated with rainfall and temperature.Final residue levels were then assessed by risk quotient（RQ）to determine the risk of ingestion and the possibility of removing pesticides by common household practices was explored.The RQ indicated acute and chronic dietary exposure risks of 4.57-7.14%and 0.58-2.09%in rice,respectively,indicating little or no health risk to Chinese consumers.These results can guide the practical application of pydiflumetofen and help minimize the environmental risks associated with its global use.（4）The adsorption and desorption behaviors of pydiflumetofen in eight different arable soils and their interaction mechanisms were studied by batch equilibrium method and infrared spectroscopy.The results showed that the adsorption and desorption behaviors of pydiflumetofen were consistent with the Freundlich isotherm model,and the values of the adsorption constant K_F-adsranged from 14.592 to 102.610.The adsorption constant K_F-ads showed a significant linear positive correlation（p<0.1）with soil organic carbon and organic matter content.Both high and low temperatures attenuated the sorption capacity of soil for pydiflumetofen.In addition,the initial p H value of the solution,ionic strength and the addition of exogenous humic acid,biochar and different types of surfactants at different concentrations also had an effect on the sorption capacity of soil.Pydiflumetofen is weakly mobile and leachable in most soils and may pose some threat to surface water and surface organisms,but does not contaminate groundwater.