Study On Four Spray Adjuvants Improving The Rainfastness Of Azoxystrobin On Maize Leaf Surfaces

Nowadays,pesticide reduction is a very important direction for pesticide research,and the use of spray adjuvants is one of the important ways to reduce the use dose of pesticide and increase its efficiency.If it rains in a short time after spraying the pesticide,some of the pesticide active ingredients on the surface of the target will be washed away due to rain erosion,which ultimately leads to a reduction in control effectiveness.So we can effectively reduce the effect of rain on the application of pesticides by adding suitable spray adjuvants to the spray solution.In the main producing areas of summer maize in China,the diseases and pests often occur in July and August.Frequent rainfall during this period will have a significant adverse impact on the control of pesticide spray in maize fields.In order to reduce the adverse effects,it is necessary to research the spray adjuvants used on maize.In this paper,the influence of the spray adjuvants(AY904-1,AY904-2,AY904-3 and AY904-4)on the contact angle,retention amount,drying time and surface tension of the azoxystrobin solution on maize leaves were investigated.And the swelling degree and solubility of the spray adjuvants and the safety of chlorobenzamide tank-mixed with spray adjuvants spraying on the safety of maize growth were also determined.Then we mainly used fluorescence microscopy studied the effect of spray adjuvants on the retention of azoxystrobin on maize leaves under different rainwater washout conditions,and screened out spray adjuvants and their concentration that can significantly improve the rainfastness of pesticides.According to the test results,we have screened two spray adjuvants and their adding concentrations that can significantly improve the washout performance of pesticides.We selected a part of the test treatment,and quantitatively determined the retention of azoxystrobin on maize leaves after rain erosion by high performance liquid chromatography.And we also found fluorescence microscopy were in agreement with a quantitative HPLC method in which the exact quantity of active ingredient on a maize leaf was determined before and after a rain wash.Finally,by measuring the effects of AY904-1 and AY904-2spray adjuvants on the control efficacy of azoxystrobin against northern corn leaf blight under simulated rainfall scouring conditions,the performance of the two spray adjuvants were more accurately evaluated.The following are the main research results.The spray adjuvants all can reduce the contact angle of the azoxystrobin liquid on the surface of maize leaves,especially the treatment of AY904-1 and AY904-2 with a mass fraction of1%.AY904-1,AY904-2 and AY904-3 can significantly reduce the surface tension of azoxystrobin liquid.What’s more,AY904-1 and AY904-2 can significantly increase the retention of the liquid on the surface of maize leaves.As the temperature rise,the stability of the spray adjuvant films decrease,the properties of AY904-1 and AY904-2 in water are relatively stable,the films are not easily broken and decomposed after being soaked for a long time.But the firms of AY904-3 and AY904-4 are unstable in water.For example,under the conditions of 18°C,the AY904-3 and AY904-4 films completely dissociated at 60 min and 45 min respectively.The results of maize growth safety tests showed that the four spray adjuvants had no adverse effects on the growth of maize and they all showed high safety to the maize.Under different rainwater scouring conditions,the influence of four spray adjuvants on the retention of azoxystrobin liquid on maize leaves was investigated.The results showed that the retention of azoxystrobin on maize leaves decreased with the increase of simulated rainfall intensity.When the rainfall interval was greater than two hours,the effect of rain erosion on the retention of azoxystrobin could be effectively reduced.Adding mass fraction of 0.25%~0.50% AY904-1 or 0.50%~0.75% AY904-2 to the spray solution can improve the ability of azoxystrobin to resist rainwater erosion on maize leaves.The overall effect of AY904-3 and AY904-4 are not ideal.Under simulated rainfall conditions,the effectiveness of 180mg/L azoxystrobin tank-mixed with AY904-1(mass fractions of 0.25% and 0.50%)and AY904-2(mass fractions of 0.50%and 0.75%)was tested for northern corn leaf blight disease.The results showed that the selected adjuvants could reduce the adverse effect of rain erosion on the application effect.After a simulated rainfall duration of 5 min and a strength of 20 mm/h,the control treatment had a control effect of 28.26% on the disease.In comparison,the mass fraction addition of0.25% AY904-1 in the treatment could still achieve 69.76% of the control effect on the northern corn leaf blight,the mass fraction addition of 0.50% AY904-2 in the treatment could still achieve 66.19% of the control effect as well.Fluorescence microscopy method has the advantages of being intuitive,simple,and easy to operate.Therefore,this paper mainly used fluorescence microscopy to evaluate the effect of spray adjuvant on the erosion of rainwater on azoxystrobin in maize leaves.The results of this study indicate that there is a good correlation between the fluorescence coverage of azoxystrobin as measured by fluorescence microscopy and the retention of azoxystrobin as measured by high performance liquid chromatography.Therefore,the method of selecting fluorescence microscopy to evaluate the retention of azoxystrobin on maize leaves is accurate and reliable.