Abstract:Randomized block design was used to evaluate the effects of four fungicides on controlling the powdery mildew of the flos lonicerae, Lonicera japonica Thunb., and HPLC was used to determine the content of chlorogenic acid. The results after 14 days of treatment showed that the 15% triadimefon WP at 600 times dilution had best control with 77.8%, followed by 15% triadimefon WP at 1 200 times dilution and 50% carbendazim WP at 500 times dilution with the control efficacy of 75.7% and 70.8% respectively, which were the most significantly higher than the control of 3% Zhongshengmycin WP at 500 and 1 000 times dilution, and 2% TF-120 SL at 1 000 times dilution. The efficacy of 2% TF-120 SL at 500 times solution was 60.3% with no significant difference from that of the former three treatments, but was higher than that of the later three treatments at 5% level of significance. The flos lonicerae treated with 50% carbendazim WP at 500 times dilution had the highest content of chlorogenic acid (1.683%) followed by the treatment (1.539%) with 50% carbendazim WP at 500 times dilution, which could meet the demands of The Pharmacopeia of the PRC. Therefore these two treatments were the first choice for controlling the powdery mildew of flos lonicerae.