Studies On Screening Of Effectual Fungicides And Mixed Preparations For Controlling Potato Late Blight

Potato late blight caused by Phytophthora infestans can lead to potato leaf death and tuber rot,and caused decline of yield and quality or even made the crop unharvestable.Potato late blight is the main critical factor affecting the production of potato and the most important disease on potato.At present,chemical control is the main method to control potato late blight.However,the misuse of chemicals has resulted in resistance to P.infestans and become increasingly serious,which affect chemicals' performance seriously.Besides development of disease-resistant variety,The application of mixed chemicals and new biological fungicides are important methods to solve resistance problem.Therefore,the following researches are carried out in the study.1.The toxicities of azoxystrobin,dimethomorph,mandipropamid,mancozeb,carbendazim,propineb on P.infestans were determined by measuring the growth rate of mycelium in laboratory.The results showed that all fungicides have good inhibitory effects on P.infestans,and the order of EC50 is: dimethomorph < azoxystrobin < mandipropamid < carbendazim < propineb < mancozeb.2.To delay the development of fungicide resistance,the toxicities of mixtures of pyraclostrohin with flupicolide and chlorothalonil were determined on P.infestans by measuring the growth rate of mycelium in laboratory,and the control effieacy on potato late blight was assessed through field test.The results showed that all mixtures exhibited additive effects on P.infestans in vitro.When the mass ratio of mixture of pyraclostrobin and flupicolide was l:5,the synergistic ratio(SR)was 1.29.When the mass ratio of mixture of pyraclostrobin and chlorothalonil was 9:1,the synergistic ratio(SR)was 1.26.Field test demonstrated that the two mixtures both had higher control efficacy,and their control effects were 86.5% and 87.4% respectively on potato late blight.3.To evaluate inhibitory activity of lisea cubeba oil on potato late blight,the toxicities of lisea cubeba oil,fluopicolide and their mixtures were determined by measuring the growth rate of mycelium in laboratory.The results showed that lisea cubeba oil have some inhibitory effect on P.infestans.When the mass ratio of mixture of lisea cubeba oil and fluopicolide was 20:1,the synergistic ratio(SR)was 1.59 and existed synergistic interactions.