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Activity of Tebuconazole on Sclerotium rolfsii and Rhizoctonia solani, Two Soilborne Pathogens of Peanut. T. B. Brenneman, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793. A. P. Murphy, and A. S. Csinos. Mobay Research Farm, Ferry Lake Road, Tifton 31794; and Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793. Plant Dis. 75:744-747. Accepted for publication 16 February 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0744.

Tebuconazole, an ergosterol biosynthesis inhibitor, had a high level of activity against Sclerotium rolfsii and Rhizoctonia solani in vitro. Mean ED50 values for inhibition of mycelial growth of two isolates each of R. solani anastomosis group 4 (AG-4) and S. rolfsii were 0.17 and 0.08 ?g/ml, respectively, for tebuconazole, compared with 24.3 and 3.9 ?g/ml, respectively, for the pentachloronitrobenzene (PCNB) standard. The ED50 values for the inhibition of sclerotia formation by S. rolfsii were 0.13 and 4.99 ?g/ml for tebuconazole and PCNB, respectively. ED50 values for inhibition of sclerotial initials were 0.14 and 2.75 ?g/ml for tebuconazole and PCNB, respectively. In the field, tebuconazole provided good control of both Rhizoctonia limb rot (R. solani AG-4) and southern stem rot (S. rolfsii) of peanut (Arachis hypogaea) when applied seven times as a foliar spray at rates of 188250 g/ha. Control of both diseases was positively correlated with a range of rates between 125 and 280 g a.i./ha. Efficacy was maintained when tebuconazole was applied as a block of sprays either at the beginning or end of the season or in an alternating schedule with chlorothalonil. Pod yield for plants in treated plots was approximately 50% greater than in those treated with chlorothalonil, which controlled late leaf spot (Cercosporidium personatum), but had little impact on the soilborne pathogens.