Abstract:In view of the prevalence of green spot disease in Citrus sinensis Osbeck base in Chongqing, its symptoms and the shapes of its pathogens were observed. The separation of its pathogens and the determination of its pathogenicity were also conducted. The results showed that Citrus sinensis green spot disease was a new disease caused by Apatococcus lobatus of Chlorophyta. Effective concentration (EC50) of 50% carbendazim+mancozeb WP, 62.25% myclobutanil+mancozeb WP, 10% difenoconazole WG, 25% bromothalonil WP and 53.8% copper hydroxide DF to inhibit the growth of Apatococcus lobatus was 2.3531, 2.6234, 9.3815, 13.8816 and 28.9808 mg/kg by toxicity tests in the laboratory, respectively. The control effect of 600 times 50% carbendazim+mancozeb WP, 600 times 62.25% myclobutanil+mancozeb WP to the growth of Apatococcus lobatus by field tests was higher than that of 1 000 times 10% difenoconazole WG, 1 000 times 53.8% copper hydroxide DF and 600 times 25% bromothalonil WP. There was significant differences between treatments by Duncans test.