Abstract:Cucumber seed and seedling was imbibed and sprayed respectively to evaluate the safety of tetraconazole to cucumber, while the sensitivity of Sphaerotheca fuliginea to tetraconazole was tested with cotyledon assay and field experiment was also conducted at the same time. The inhibitory rates to powdery mildew, plant height, root length and increase rate of stem diameter and chlorophyll of tetraconazole were lower than that of hexaconazole after seed-soaking treatment. Inhibition to internode length was slight when tetraconazole was used at the different periods of cucumber growth. The EC50 of tetraconazole against S.fuliginea was 0.8146 mg/L, so the sensitivity of this pathogen to tetraconazole was much higher than that to kresoxim-methyl. The control efficacies were 76.02%- 85.77% 7 days after last treatment in field. The study indicated that tetraconazole was safety to cucumber in the whole growth period. It has a long application interval and can be used as an alternative fungicide in cucumber powdery mildew control.