Tolclofos-methyl was compared to PCNB in vitro to determine its relative activity against four isolates of Sclerotium rolfsii Sacc. and two isolates of Rhizoctonia solani Kuehn. Concentrations of 0.001, 0.01, 0.1, 1.0 and 10 μg/mL of each of the fungicides were used to evaluate their effects on radial growth on both S. rolfsii and R. solani and their effects on sclerotia formation and sclerotial germination of S. rolfsii. Little difference in efficacy between the fungicides occurred for S. rolfsii. However, tolclofos-methyl reduced radial growth of R. solani more than PCNB at concentrations of 0.1 and 1.0 μg/mL. In field tests in 1982 and 1984 tolclofos-methyl at 5.6 kg ai/ha or less was as effective or superior to PCNB or PCNB-fensulfothion in reducing incidence of southern stem rot and increasing yield. In 1984, tolclofos-methyl at 8.4 kg ai/ha reduced Rhizotonia limb rot damage over the control, but PCNB at 11.2 kg ai/ha did not.