In Vitro Sensitivity of Rhizoctonia solani and Other Multinucleate and Binucleate Rhizoctonia to Selected Fungicides. D. E. Carling, University of Alaska Fairbanks, Agricultural and Forestry Experiment Station, Palmer 99645. D. J. Helm, and R. H. Leiner. University of Alaska Fairbanks, Agricultural and Forestry Experiment Station, Palmer 99645. Plant Dis. 74:860-863. Accepted for publication 6 April 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0860.

Isolates of Rhizoctonia solani, R. zeae, R. oryzae, and binucleate Rhizoctonia, including representatives of 11 anastomosis groups of R. solani, were exposed to a range of concentrations (0, 0.01, 0.10, 1.00, or 10.00 mg a.i./L) of five fungicides (benomyl, hexaconazole, iprodione, PCNB, and prochloraz) in vitro. EC₅₀ values were determined for each fungus-fungicide combination. All isolates were highly sensitive to hexaconazole (EC₅₀ values less than 1 mg a.i./L), and most isolates were moderately sensitive (EC₅₀ values between 1 and 10 mg a.i./L) to the other four fungicides. The EC₅₀ values for R. zeae, R. oryzae, and similar isolates frequently were much lower or much higher than those for isolates of R. solani or binucleate Rhizoctonia, but they did not follow a consistent pattern. EC₅₀ values based on radial growth were as much as 10 times greater than EC₅₀ values based on dry weight.