Screening And Application Of Insecticides For Control Of Northern Corn Leaf Bright

Northern corn leaf blight,caused by Exserohilum turcicum（Pass.）Leonard&Suggs,is an important leaf disease in maize in middle and late growth.The annual incidence rate of northern corn leaf blight was 10%-30%in maize growing areas of Shaanxi Province,and50%-70%in years with more rainfall in summer.The whole maize plant basically died in reoccurring areas,which posed a serious threat to maize production in Shaanxi Province.In recent years,the irrational application of pesticides has led to the increase of pesticide residues in the field and the continuous increase of production costs.It is urgent to select efficient pesticides,rationally apply pesticides to improve their utilization rate and reduce the use of pesticides.Therefore,the selection of high efficiency and low toxicity agents in the critical period of northern corn leaf blight prevention and control,can effectively control the disease and improve the yield of corn,to control the prevalence of northern corn leaf blight,farmers increase yield and income are of great significance.In order to screen high efficiency and low toxicity pesticides for controlling northern corn leaf blight,and to determine the best application period and times,and to provide scientific basis for disease control,70%mancozeb WP 400 times solution was studied through laboratory toxicity test and field efficacy test.15%triazolone WP 40 g/667m²;50%thiophanate-methyl SC 130 ml/667m²;40%Pyrimethanil SC 400 times solution;20%thiodiazole-copper SC 800 times solution;50%dimethomorph WP 15 g/667m²;The control effect of the 7 agents of 18.7%azoxystrobin·propiconazole WP 1300 times on the agents of northern corn leaf blight was studied.The optimal application period and application frequency were studied,and the main results were as follows:（1）Toxicity test results of 70%mancozeb WP,15%triazolone WP,50%thiophanate-methyl SC,40%Pyrimethanil,20%thiodiazole-copper SC,50%dimethomorph WP and 18.7%azoxystrobin·propiconazole WP in laboratory showed that,18.7%azoxystrobin·propiconazole WP and 50%thiophanate-methyl SC had the best control effect against northern corn leaf blight,with EC₅₀ of 0.17μg/m L and 0.96μg/m L,respectively.The control effect of 20%thiodiazole-copper SC,40%pyrimethanil SC and 15%triazolone WP was relatively poor,with EC₅₀ greater than 10μg/m L.（2）The results of field efficacy test of 7 insecticides showed that the control effect of each insecticide on northern corn leaf blight was 16.35%-99.01%.Among them,18.7%azoxystrobin·propiconazole WP 1300 liquid treatment had the best control effect,which was99.01%.The control efficiency of 70%mancozeb WP 400 times liquid was 92.31%.From the point of view of yield increase rate,the yield of maize after treatment with each agent increased compared with blank control,and the yield increase ranged from 12.05%to72.35%.Among them,the treatment of 18.7%azoxystrobin·propiconazole WP 1300 times liquid had the highest yield increase rate of 72.35%,followed by the treatment of 50%dimethomorph 15g/mu,the yield increase of 60.23%.（3）The protective and therapeutic effects of 50%thiobacillam methyl SC on northern corn leaf blight were studied.The results showed that the control effect of 50%thiobacillam methyl SC on northern corn leaf blight could reach 100%within 3 days before inoculation,and the control effect of 50%thiobacillam methyl SC on northern corn leaf blight could reach more than 90%during 5 to 10 days before inoculation.There was no significant difference（100%）between application of methyl thiobacillazim 12 and 24 h after inoculation and application of thiobacillazim 3 d before inoculation.However,the control effect of thiobacillazim methyl at 48h after inoculation was significantly reduced to only77.6%.The results showed that protective application was better than therapeutic application in the prevention and treatment of northern corn leaf blight.（4）The treatments were applied 3 times,2 times and 1 time at the occurrence of water stains on maize leaves,and 3 times,2 times and 1 time at the obvious spots on maize leaves,respectively.The results showed that the control effect of each treatment on northern corn leaf blight was 55.76%～99.84%.The best control period of northern corn leaf blight was about 10 days before maize leaves were infected.After maize leaves were infected with water stains on the leaves began to spray agents,the control effect is excellent.The preferred agent was 18.7%azoxystrobin·propiconazole,with a dose of 1300 times of liquid and 3times of administration,once every 7 days.