Sensitivity of Binucleate Rhizoctonia spp. and R. solani to Selected Fungicides In Vitro and on Azalea Under Greenhouse Conditions. T. A. Frisina, Graduate Research Assistant, North Carolina State University, Raleigh 27695. D. M. Benson, Professor, North Carolina State University, Raleigh 27695. Plant Dis. 72:303-306. Accepted for publication 20 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0303.

Benomyl, benodanil, chlorothalonil, and iprodione were evaluated in vitro for inhibition of linear growth of binucleate Rhizoctonia spp. (BN2 and BN8) from Rhododendron sp. with web blight and Rhizoctonia solani (RS15) from Ilex crenata ‘Helleri’ with leaf blight. Isolates of binucleate Rhizoctonia spp. and R. solani were sensitive (ED₅₀ < 1.1 ?g a.i./ml) to all fungicides tested in vitro. Dosage-response curves were similar for isolates of binucleate Rhizoctonia spp. and R. solani grown on potato-dextrose agar (PDA) amended with benodanil and iprodione. Dosage-response curves were steeper, on a log-probit basis, for R. solani grown on PDA amended with benomyl or chlorothalonil than for binucleate Rhizoctonia spp. Levels of inhibition of 14 selected isolates of binucleate Rhizoctonia spp. and four isolates of R. solani were normally distributed at ED₅₀ concentrations of the fungicides. Benomyl, benodanil, and iprodione were evaluated under greenhouse conditions for efficacy of control of web blight (suppression of aerial mycelium) on azaleas inoculated with virulent isolates of binucleate Rhizoctonia spp. (BN2) and R. solani (RS25). Both binucleate Rhizoctonia spp. and R. solani responded similarly to fungicide treatments; the drenches of iprodione and the sprays of benomyl, benodanil, and iprodione effectively limited aerial mycelial growth.