Epidemic regularity and chemical control of tobacco Corynespora leaf spot in Ji'an

In order to prevent and control the leaf spot of flue-cured tobacco caused by Corynespora cassiicola （Berk. ＆ Curt.） Wei，the occurrence of this Corynespora leaf spot in different climates，breeds，soil types， cultivation and management conditions was investigated and researched，and the regular epidemic pattern of this disease in Ji'an was analyzed. The toxicities of 10 fungicides including Prochloraz ME，Dimethachlon WP， Epoxiconazole SC，Difenoconazole WG，Tebuconazole SC，Boscalid WG，Procymidone EC，Iprodione SC， Pyraclostrobin EC，Polyoxin B WP were determined by the radical growth rate of poison of medium culture method. And above six fungicides were used to control flue-cured tobacco leaf spot in the field trial. The results showed that Corynespora leaf spot of flue-cured tobacco attacked in end of May and early June in Ji'an，and especially early in dry farmland. High temperature and raininess in late June was better for epidemic outbreak. The disease resistance of Breed K326 was relatively good，but in 4 kinds of soil types，such as eel mud，hydromorphic alluvial sandy mud，purple mud and hydromorphic tide sandy mud，it was attacked by this disease. Prochloraz，Dimethachlon and Boscalid showed good inhibition on the growth rate of C. cassiicola，the values of EC50 were 1.012，1.085 and 1.503 mg/L respectively. The values of EC50 of other seven fungicides were between 3.542 mg/L and 7.650 mg/L. Field trial results showed that Dimethachlon had better effect on flue-cured tobacco leaf spot，the control effects was 66.94%-72.91%，and the control effects of Boscalid and Epoxiconazole were 68.62% and 63.93%. The results suggest that preventing and controlling flue-cured tobacco leaf spot need to combine weather factors and use fungicides at early stage according to the epidemic regularity. And the further study of fungicides of this disease should be needed.