Screening Of Effective Fungicides For Potato Black Scurf And Field Control Experiment

Potato black scurf,caused by Rhizoctonia solani Kühn,is widely distributed in most potato planting areas,and it has become one of the most serious diseases in the potato production in China.The disease is common in the main potato producing areas in China and is getting worse year by year,which affects the yield and quality of potatoes and seriously hinders the development of potato industry.The most popular and effective management strategy for controlling potato black scurf disease in China is the application of synthetic fungicides.In order to screen out effective fungicides for controlling potato black scurf,the mycelial growth rate method was used in this study and the indoor toxicity of 18 fungicides to Rhizoctonia solani Kühn was determined by the mycelium growth rate method.Based on thifluzamide,fludioxonil and pyraclostrobin,the combined indoor toxicity of fungicides with higher bacteriostatic activity compared with other fungicides at different ratios was determined by mycelium growth rate method,and the best ratio was screened out.After that the suspension seed coating agent was processed for indoor safety test and field efficacy test.The purpose was to provide basis for reasonable selection and comprehensive control of fungicides for controlling potato black scurf in the field.The indoor toxicity of 18 fungicides such as difenoconazole,phylloconazole,tebuconazole,myclobutanil,thifluzamide,fludioxonil,azoxystrobin,pyraclostrobin,prochloraz,captan and iprodione to Rhizoctonia solani Kühn was determined by mycelium growth rate method.The results showed that tebuconazole,fludioxonil,phyllostazol,prochloraz,myclobutanil and thifluzamide had good inhibitory effects on Rhizoctonia solani Kühn,with EC₅₀ of 0.0631,0.1188,0.1198,0.2262,0.2465 and 0.3060mg·L^-1 respectively.Pyraclostrobin,iprodione,difenoconazole,captan also had good inhibitory effects on the Rhizoctonia solani Kühn,with EC₅₀ of 2.1370,2.1788,4.2460,8.9983 and 12.2892mg·L^-1respectively.In addition,other fungicides had certain inhibitory effects on Rhizoctonia solani Kühn.Fludioxonil,thifluzamide and pyraclostrobin had good inhibitory effects on Rhizoctonia solani Kühn and were all registered in China,so fludioxonil,thifluzamide and pyraclostrobin were the main components and were compounded with other fungicides with higher antibacterial activity.The combined toxicity of fludioxonil,thifluzamide and pyraclostrobin to Rhizoctonia solani after being compounded with several fungicides with higher antibacterial activity was determined by mycelium growth rate method.The combined toxicity showed that the co-toxicity coefficient（CTC）of fludioxonil and tebuconazole,phylloconazole,myclobutanil,difenoconazole,iprodione and azoxystrobin were the largest when the ratio was1:5,1:5,1:1,1:1,5:1 and 20:1,respectively.The co-toxicity coefficient（CTC）of thifluzamide and tebuconazole,tebuconazole,myclobutanil,triadimefon,difenoconazole,iprodione,pyraclostrobin,azoxystrobin,fludioxonil and captan in the ratio of 1:5,1:10,1:10,5:1,10:1,1:1,10:1,5:1 and 20:1 were the largest and the synergistic effect was the most significant.The co-toxicity coefficient（CTC）of pyraclostrobin and tebuconazole,tebuconazole,myclobutanil,triadimefon,difenoconazole,fludioxonil,iprodione,azoxystrobin and captan were the largest and the synergistic effect was the most significant when the ratio was 1:10,1:20,1:5,10:1,1:10,5:1,5:1 and 1:1 respectively.According to the indoor combined toxicity test results,6%thifluzamide-fludioxonil suspension seed coating agent was prepared with thifluzamide:fludioxonil ratio of 2:1 as the optimal ratio,and the indoor safety test and field efficacy test were conducted.The indoor safety test results showed that 6%thifludioxonil suspension seed coating agent had the following effective components:250 g/100 kg of seeds,375 g/100 kg of seeds,500 g/100 kg of seeds,625 g/100 kg of seeds.The plant height,root length,fresh weight and growth rate of potato were affected to different degrees,and the morphological and color characteristics of potato leaves were observed at different periods,without obvious phytotoxicity.Field efficacy tests were conducted in Feicheng and Liangzhuang of Tai’an respectively.During the whole growth period of potato,the control effect of 6%thifludioxonil suspension seed coating agent250 g/100 kg seed treatment was the best,which was better than that of 25%azoxystrobin suspension agent,25 g·L^-1 fludioxonil suspension seed coating agent.