Abstract: Toxicities of 20 fungicides and co-toxicities between propiconazole or azoxystrobin and difenoconazole on Phomopsis asparagi were determined by the pathogen′s mycelium growth rates under treatments.The results showed that prochloraz,difenoconazole,epoxiconazole,tebuconazole,chlorothalonil and thiabendazole had higher toxicities among all,with prochloraz being the strongest showing an EC50 of 0.035 5 mg·L-1.Mancozeb,hymexazol,thiram,pyrimethanil,jinggangmycin,copper calcium sulphate and oligosaccharin were not as potent.The co-toxicity efficient(CTC) between difenoconazole and propiconazole(1∶1) was 123.42,suggesting existence of synergism.The synergisms between difenoconazole and azoxystrobin,on the other hand,were reflected by the CTCs of 164.17,132.91 and 141.91 when their mixing ratios were 8∶5,1∶5 and 1∶8,respectively.