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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.