Fungal toxicity testing indicated that the inhibition of eight kinds of fungicides against brown spot of yacon were very different and their toxicity from high to low were followed by 325g/L benzoic,azoxystrobin,10%difenoconazole file,206.7g/Ldioxanone flusilazole,125g/L epoxiconazole,250g/L pyrazole azoxystrobin,60% ether metiram,50% water kresoxim and 46% cupric hydroxide respectively,and 325g/L Benzene armour was the best inhibition.Its EC50 was only 0.28mg/L.