Improved Efficacy Of Pyraclostrobin By Formulation Optimization And Spray Adjuvant Addition Against Cucumber Powdery Mildew And Its Mechanism

The National Green Agriculture Development Plan of the 14th five-year Plan points out that in China’s agricultural production,we should continue to promote the plan of pesticide reduction and efficiency,carry out green prevention and control,and promote the scientific use of drugs.Therefore,it is of great significance to tap the potential of pesticide preparations to improve the effect of pesticide use and to improve the utilization rate of pesticides in different ways.In this paper,the effect and mechanism of SC particle size and EC solvent on the control of cucumber powdery mildew were studied by using pyraclostrobin as model pesticide and powdery mildew at different stages.The effect and synergistic mechanism of spray adjuvants on the control of cucumber powdery mildew by pyraclostrobin SC and EC were clarified.The results provide a theoretical basis for the reduction and scientific use of pesticides.The specific contents and results are as follows:1.Pyraclostrobin SC with average particle size D₅₀of 1μm,3μm and 5μm and pyraclostrobin EC using dimethylbenzene and methyl oleate as solvents were prepared,and their control effects on cucumber powdery mildew were determined in the no disease,early and middle stages of the disease.The results showed that when the concentration of the diluent was 200 mg/L,the control effects of average particle size D₅₀of 1μm,3μm and 5μm pyraclostrobin SC on cucumber powdery mildew were significantly different.The control effect from high to low is 1μm>3μm>5μm.It was determined that the control effect of pyraclostrobin SC on cucumber powdery mildew could be improved by reducing the particle size.Pyraclostrobin EC with methyl oleate as solvent can control cucumber powdery mildew by more than 80%at 200 mg/L,which is higher than that of dimethylbenzene solve EC,and is safe to cucumber and can meet the requirements of prevention and control of cucumber powdery mildew,so it can be used as a substitute for conventional aromatic solvent dimethylbenzene to prepare dimethylbenzene EC.2.The control effect of pyraclostrobin on the cucumber powdery mildew was compared when it was applied to different stages of cucumber powdery mildew（no disease,early stage and middle stage）.In the no disease,early stage and middle stage of cucumber powdery mildew,the control effect was gradually reduced by applying pyraclostrobin SC and EC preparation respectively.Compared with the no disease,in the early and middle stages of the disease,the control effect decreased by 15%-27%and 53%-70%,respectively.With the continuous development of powdery mildew,the hydrophobicity of cucumber leaves was increasing,the wetting and retention on the surface of cucumber leaves were reduced.Compared with pyraclostrobin SC,the control effect of pyraclostrobin EC preparation increased by 13%-22%,18%-30%and 60%-95%in the three application periods,respectively.Pyraclostrobin EC had more advantages in the middle stage of serious disease of white powder.3.The control effects of pyraclostrobin SC and EC added with four spray adjuvants on cucumber powdery mildew were compared.The control effect of pyraclostrobin on cucumber powdery mildew was significantly improved after using four kinds of spray adjuvants.After adding four kinds of spray auxiliaries,the control effects of two kinds of pyrazolyl carbendazim on cucumber powdery mildew in different periods were significantly improved,and the synergistic effect of spray auxiliaries was more significant in the middle stage of cucumber powdery mildew.It can increase the control effect by 15%-20%.In the no disease and early stage of cucumber powdery mildew,the synergistic effect of cationic surfactant Gemini-31551 was significantly higher than that of Silwet-618,AEO-5 and GY-Tmax;but in the middle stage of cucumber powdery mildew,the synergism of Gemini-31551 was significantly lower than that of the other three auxiliaries.4.The interfacial behavior of pyraclostrobin SC and EC added with four spray adjuvants on cucumber leaves were compared.By using four kinds of spray adjuvants,the surface tension of the pesticide diluents can be reduced from 40-60 m N/m to 20-35 m N/m,and the contact angle of the droplets on the surface of cucumber leaves can be reduced to below 65°,and the adhesion tension can be kept greater than 20 m N/m,increase the diffusion coefficient,increase the wetting area by 2-10 times,and improve the wetting and retention performance of the droplets on the cucumber leaves.At the same time,it can shorten the evaporation time of the droplets by 20%-60%,and reduce the liquid loss of droplets bouncing,gathering and sliding off leaves.By affecting these interfacial behaviors,it led to the improvement of pesticide efficacy.