Research Of Screening And Application Of New Fungicides For Preventing And Controlling Corn Northern Leaf Blight

Corn northern leaf blight (CNLB) is one of the main diseases on maize. It issignificant to control the disease for ensuring and increasing the maize yield.Currently, there are only4agents against CNLB. So the novel prevention drugs havegreat development value and wide market prospect. Relying on Shenyang ResearchInstitute of Chemical Industry, State Key Laboratory of the Discovery andDevelopment of Novel Pesticide, in this study,40new high bioactivity compoundsand common pharmaceuticals had been screened and the effective drug preventingand curing CNLB had been determined. Based on this, a series of experiments,including the optimization of the instituents proportions, the screening of mixturerecipe, the construction of the method for active ingredients analysis, observation ofthe indoor properties and field efficacy trials research, were carried. The results weresummarized as follows.1.39active compounds and new pesticides were screened in vitro. EC50values of11of them were detected and the virulence regression equations were established. Thefungistatic effects in vitro were accurately assessed. The result indicated thatprochloraz, difenoconazole and SYP-14288had good fungistatic effects, especiallythe prochloraz did whose EC50value reached0.0003mg/L. Among these components,SYP-14288was the one independently researched and developed by ShenyangResearch Institute of Chemical Industry and worth being investigated further. Besides,the study also demonstrated that the fungistatic effects of strobilurin fungicides invitro was not as good as what had been reported. Their controling effects remained tobe comfirmed by pot experiment.2. In order to acquire suitable materials for in vivo test, the conditions for inducingCNLB indoor had been optimized by orthogonal experimental design. The seedlingaged two leaves stage was choosen to induced at20-25℃in the atmosphere with more than90%humidity. The inoculum concentration was1×106cells/mL. Besides,the Wuke2ndwas determined as the trail material through breed-assensitivity study.3. The result of protective activity test for pot plants showed that difenoconazole,fludioxoni and prochloraz had good protective activity to the plants injectedExserohilum turcicum and their EC90values (mg/L) reached14.29,48.38and60.02.The EC90values (mg/L) of control agents propiconazole and pyrazole kresoxim,reached35.25and70.97. The protective activity of difenoconazole was higher thanthat of propiconazol while the protective activity of fludioxoni and prochloraz washigher then that of pyraclostrobin and lower then that of propiconazol. The protectiveactivity of the new marketed drugs pyraoxystrobin independently researched anddeveloped by Shenyang Research Institute of Chemical Industry remained normal andthe EC90value reached171.75mg/L.4. The protective activity of the suspension concentrates for pot plants in green housewas tested and the result indicated that the pesticide effects of prochloraz+pyraoxystrobin and propiconazole+pyraoxystrobin suspension concentrates weresimply added or weakened. They both can not be applied to prevent and control theCNLB. The cotoxicity coefficients of the difenoconazole+pyraoxystrobin,fludioxoni+pyraoxystrobin and propiconazole+pyraoxystrobin with the mass ratio3:1and1:1exceeded120, performing as synergized action, with a good protectiveactivity. Among them, the protective activity of the difenoconazole+pyraoxystrobinwith the mass ratio3:1was the highest, with the EC90value being15.24. The furtherstudy including recipe screening should be conducted.5.The recipe of30%difenoconazole+pyraoxystrobin suspension concentrate(DPSC),contained20.0%difenoconazole pyraoxystrobin,10.0%NNO,2%EL-60,1%NP-10,1%white carbon black,0.1%xanthan gum,0.5%WJX,5%Glycol and diluted waterupto100%, was determined through recipe selection and heat storage stability trail.The component analytic result of30%DPSC prepared according to the recipe aboveindicated that it contained no less than20%difenoconazole and10%pyraoxystrobin.The pH value varied from5.0-8.0. The suspensibility reached90%. The wet sieve testshowed that the proportion of the constituents through the44μm sieve reached98%.The pourabilioty, microtherm stability and heat storage stability all met standards.6. The study on indoor effect properties of30%DPSC showed that the DPSC with mass radio of2:1had an obvious inhibition effect on the CNLB caused by Exserohilumturcicum and the EC90values reached13.8167mg/L. It had good protective activity. TheSC had great security and a long validity period which reached10d at40mg.L-1.However, the absorption action trail of the roots and leaves indicated that thepreventing and controlling effect of400mg/L DPTC with mass ratio2:1only reachedapproximately50%, which demonstrated its low absorption activity. Besides, therainfall intolerance of the DPSC remained low level.7. The result of field efficacy trials for30%difenoconazole+pyraoxystrobinsuspension concentrate (DPSC) indicated that30%DPSC had good control efficacyfor CNLB. The control efficacy reached80%under low dose. Compared with those incontrol area, the corns in treatment area growed well, whose leaves were green, withlittle lesion. Under the same dose, the30%DPSC had asimilar control efficacy withthe control agent. Under high dose, the30%DPSC remained good control efficacyand showed no significant difference with the efficacy of18.7%propiconazol+Azoxystrobin SC. The control efficacy approximately reached80%.The corns in Changchun test site were planted earlier and the lesions had occurredbefore the primary fungicide application. This trail can be conducted as the curativeactivity test for these suspension concentrates. The result showed that30%DPSC hadgood curative efficacy for the injected plants in an early phase.