Screening And Effect Evaluation Of Insecticides Suitable For Electric Heating Application Method

In recent years,there has been a steady increase in the planting area of protected cultivation.Due to the suitable conditions in protected cultivation,high temperature and high humidity environments provide potential conditions for the occurrence of pests and diseases.At present,pesticide spraying is the main application method to control pests and diseases in protected cultivation.Pesticide spraying has several disadvantages,including being time-consuming and labor-intensive.Additionally,it can increase air humidity and may have low application efficiency.As a type of pesticide formulation,the smoke generator offers several advantages such as labor-saving and water,no increase in environmental humidity,and no delay in farming operations,in comparison to traditional pesticide spraying methods.However,there are few types of currently registered insecticides smoke generator and single active ingredients,which are difficult to meet the needs of production.Therefore,there is an urgent need for an efficient and labor-saving pesticide application technology to control pests and diseases in protected cultivation.In this study,the electric heating method with controllable temperature and stable heat source was used to apply pesticides based on the principle of an electrothermal sulfur evaporator.The feasibility of applying common pesticides by electric heating was evaluated from six aspects:thermal stability,smoke formation rate,biological activity,deposition uniformity,crop safety and field test.The main results are as follows:1.The minimum smoke temperature and thermal stability of 12 insecticides such as flonicamid were determined by TGA technology.The residual mass of thiacloprid at 319.79°C was 89.21%,and the residual mass of clothianidin at 238.31°C was 79.07%.The two insecticides of thiacloprid and clothianidin were not suitable for the application of electric heating at low temperature in this study,and were more suitable for development as conventional smoke generators.2.Through the determination of the smoke formation rate of insecticides,insecticides that meet the development standards of smoke application were screened out.Flonicamid,acetamiprid,bifenthrin,lambda-cyhalothrin and deltamethrin had a smoking rate of more than 80%,which met the requirements of smoke application preparation.3.The biological activities of acetamiprid,flonicamid,bifenthrin,lambda-cyhalothrin and deltamethrin against Bemisia tabaci and Aphis gossypii were tested in a 0.3 m³ closed device at the same dosage（0.01 g active ingredient）.Among them,the better ones are flonicamid and acetamiprid.4.The dispersion of active ingredients on target crops has always been a major problem in pesticide applications,and pesticide adjuvants can play a positive role in the diffusion of active ingredients.In this study,the adjuvant NH₄Cl suitable for electric heating was selected by adding different types of adjuvants.With the increase of NH₄Cl content,the deposition of active ingredients of insecticides in the vertical direction tends to be uniform,which can be uniformly deposited on crop leaves.5.The safety of two insecticides,flonicamid and acetamiprid,on cucumber was verified in a greenhouse.In the safety test,there was no significant difference in plant height and stem diameter of cucumber after 7 d of flonicamid and acetamiprid smoke treatment compared with the control treatment,and no phytotoxicity symptoms occurred.6.The field test results of flonicamid and acetamiprid after electric heating application on B.tabaci and A.gossypii showed that the control efficiency of electric heating application was higher than that of spray application under the same active ingredient dosage,and the control efficiency against pests on middle and lower canopy of cucumber was higher than that of spray application.There was no phytotoxicity symptom in the smoke point and surrounding crops of electric heating application.The results showed that it was feasible to control B.tabaci and A.gossypii by electric heating.In summary,we screen for insecticides by producing smoke through electric heating in this study.It was found that the insecticide will also produce smoke and work after reducing the temperature at the time of application.Therefore,the method of generating smoke by electric heating expands the screening range of pesticides,breaks through the high temperature stability limit of chemical smoke,and has great potential for development and application.