Abstract A set of 78 Rhizoctonia solani isolates from Shanghai, China, were examined for their sensitivity in vitro to four demethylase inhibitor (DMI) fungicides, epoxiconazole, difenoconazole, hexaconazole, and tebuconazole, by the mycelial growth rate method. The isolates were very sensitive to the four DMI fungicides. The ranges and means of the EC50 values were 0.004–0.045 and 0.014?±?0.007?μg?ml?1 for epoxiconazole, 0–0.103 and 0.010?±?0.016?μg?ml?1 for difenoconazole, 0.001–0.078 and 0.011?±?0.013?μg?ml?1 for hexaconazole, and 0.001–0.210 and 0.034?±?0.035?μg?ml?1 for tebuconazole, respectively. The frequency distribution of the EC50 values showed a normal curve for epoxiconazole and an approximately unimodal curve for difenoconazole, hexaconazole, and tebuconazole. There was no correlation between the sensitivities of the R. solani population to any two of the four fungicides (r?90.0% at 75?g.a.i.?ha?1, 80.0%–90.0% at 75?g.a.i.?ha?1 and 80.0%–90.0% at 97?g.a.i.?ha?1, respectively; these values are significantly higher (p?
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