Abstract:Pyrametostrobin 20 EC and SYP-3998 20 SC were two strobilurin candidate fungicides. Preventive, curative and duration of control of two fungicides against cucumber downy mildew were determined by potted plant spray-leaf disc test, leaf disc spray test, and potted plant spray-leaf disc test, and eradicative action of them against cucumber downy mildew were determined by detached leaves test and leaf disc test. The results showed that, pyrametostrobin 20 EC and SYP-3998 20 SC has good preventive, curative and eradicative activity against cucumber downy mildew. The eradicative action of the two candidate fungicides was reflected by their strong inhibition of the lesion extension, production of sporangia, and reinfection of sporangia, and by obvious decreasing pathogenicity of sporangia mixed with the two candidate fungicides. Moreover, pyrametostrobin 20 EC and SYP-3998 20 SC can provide the effective control of cucumber downy mildew 7-10 days after foliages spray. The preventive, curative and eradicative activity of pyrametostrobin 20 EC is higher than that of SYP-3998 20 SC and azoxystrobin 25 SC, the same with duration of control.