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.

Key words: Phomopsis asparagi, toxicity, co-toxicity efficient, fungicide