Improving The Application Effect Of Pyraclostrobin Microcapsules On Peanut Foliage By PEG Used As Capsule Shell Material

After foliar spraying,the conventional pesticide formulations,like emulsifiable concentrate and suspension concentrate,are easy to be degraded and lost by the environmental factors such as light,wind,rain,and microorganism.It not only reduced the utilization rate of pesticides,but also increased the pressure and hidden danger on environment.Compared with conventional formulations,pesticide microcapsules（MCs）have the advantages of long duration and high biological selectivity.However,it was found that not all pesticide MCs had ideal application effects in practical application.Previous studies shown that the application effect of pesticide MCs is related to the characteristics of the MCs shell.By regulating the characteristics of the MCs shell to achieve controlled release of pesticides and enhance the leaf retention capacity of the MCs is an effective way to improve the application effect of pesticide MCs.Polyethylene glycol（PEG）,with excellent environmental compatibility and biodegradability,is widely used in the preparation of pesticide MCs by interfacial polymerization.In this study,a series of pyraclostrobin loaded MCs with the different shell characteristics were prepared by regulated the molecular weight and usage of PEG in the MCs preparation system.The effects of PEG molecular weight and content on the properties of pyraclostrobin loaded MCs were investigated by characterize the morphology,leaf adhension capacity,release property and photolysis resistance of them.By the field experiment of peanut leaf spot control,the correlation mechanism between the properties of pyraclostrobin loaded MCs and the control effect against disease was clarified.The results were as follows:1.The pyraclostrobin loaded MCs were prepared by interfacial polymerization with PEG200/400/800/1500 and 2%,4%,8%,15%usage of PEG400,respectively.Through morphology observation,particle size analysis and encapsulation efficiency determination,the eight kind pyraclostrobin loaded MCs prepared in this study have the similar particle size,D₅₀was about 5μm,and the encapsulation rates of them were higher than 98%.By observing the morphology of pyraclostrobin loaded MCs deposited on the solid interface,it was found that the deformation and adhesion of the MCs were enhanced with the increase of PEG molecular weight,and the MCs were more hollow and collapsed,and there was obvious adhesion between the MCs.However,with the increase of PEG400 usage,the pyraclostrobin loaded MCs only showed the improvement of adhesion.2.Through the experiment of the leaf retention property of pyraclostrobin loaded MCs,it was found that with the increase of PEG molecular weight,the leaf retention capacity of MCs was improved significantly,and the resistance rain erosion ability was significantly improved.With the increase of PEG400 usage,the leaf retention property of pyraclostrobin loaded MCs was significantly improved as well.3.The release kinetics of pyraclostrobin loaded MCs showed that with the increase of PEG molecular weight,the release property of MCs was significantly improved.The pyraclostrobin loaded MCs prepared by PEG1500 had the fastest release speed.At the last time detection,the cumulative release amounts of pyraclostrobin loaded MCs prepared by PEG200,400,800 and1500 were 80.61%,90.98%,94.07%and 97.40%,respectively.Among the pyraclostrobin loaded MCs prepared by PEG400 with different usages,the release properties of 4%,8%and15%pyraclostrobin loaded MCs were similar,which were better than 2%usage of PEG pyraclostrobin loaded MCs,At the last detection,the cumulative release of the four MCs were88.51%,93.12%,95.21%and 94.18%,respectively.4.The anti UV degradation property of pyraclostrobin loaded MCs was tested.It was found that the anti-UV degradation property of pyraclostrobin loaded MCs decreased with the increase of PEG molecular weight.After 5 hours of UV irradiation,the residual amounts of pyraclostrobin in PEG200,400,800 and 1500 MCs were 47.29%、41.55%、39.08%and 35.93%,respectively.Among the pyraclostrobin loaded MCs prepared with different content of PEG400,4%,8%and 15%content of the pyraclostrobin loaded MCs had no significant difference in the anti UV degradation ability.2%PEG usage of pyraclostrobin loaded MCs had the best anti-UV degradation property.After 5 hours of photolysis,the residual amount of the pyraclostrobin was16.67%,and the other three were 12.17%,10.24%and 11.22%respectively.5.In the field experiment of the different pyraclostrobin loaded MCs on peanut leaf spot,the pyraclostrobin loaded MCs treatment group had a longer duration than the pyrazoxystrobin EC control group,and there were differences in the control effect among different types of pyraclostrobin loaded MCs.In the treatment of pyraclostrobin loaded MCs with different molecular weight PEG,the control effect of peanut leaf spot increased with the improvement of pyraclostrobin loaded MCs release property and leaf adhesion,and the control effect of pyraclostrobin loaded MCs prepared by PEG1500 was the highest.With the usage of PEG400increased,the effect of pyraclostrobin loaded MCs on peanut leaf spot has gradually increased.Although there was a small amount of precipitation after the application of PEG,the MCs prepared by PEG had good adhesion and still maintained a high control effect.The above results showed that the release performance,anti-UV degradation property,shell flexibility and leaf adhesion of pyraclostrobin loaded MCs can be controlled by adjusting the molecular weight and usage of PEG during the preparation of pesticide MCs by interfacial polymerization.Compared with the different usage of PEG,the molecular weight of PEG has more significant effect on the property of pyraclostrobin loaded MCs.Among them,the pyraclostrobin loaded MCs prepared by PEG1500 have the highest leaf adhesion ability and the best release property,which was conducive to reducing the secondary loss of pesticides and improving the utilization rate of pesticides,and has application potential for the prevention and control of leaf diseases.