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Activity of Tebuconazole on Cercosporidium personatum, a Foliar Pathogen of Peanut. T. B. Brenneman, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793. A. P. Murphy, Mobay Research Farm, Ferry Lake Road, Tifton, GA 31794. Plant Dis. 75:699-703. Accepted for publication 30 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0699.

The different modes of action of chlorothalonil and the ergosterol biosynthesis inhibiting (EBI) fungicides tebuconazole and diniconazole on Cercosporidium personatum were exhibited in in vitro studies. Chlorothalonil effectively prevented germination of conidia at rates as low as 0.1 μg/ml, whereas conidia exposed to high rates (100 μg/ml) of either EBI were able to use stored ergosterol and germinate. Diniconazole and tebuconazole effectively inhibited mycelial growth and sporulation at concentrations of 0.1 and 1.0 μg/ml, respectively. In the field, tebuconazole effectively controlled late leaf spot (C. personatum) of peanut (Arachis hypogaea) at the lowest rate tested (188 g/ha). Efficacy of tebuconazole was essentially equivalent to chlorothalonil (1,260 g/ha) as measured by visual disease ratings. The percentage of reflectance recorded by a multispectral radiometer indicated that plants treated with tebuconazole had more green leaf area than those treated with chlorothalonil. Significantly higher yields were also obtained with tebuconazole. Tebuconazole provided effective control of late leaf spot when applied full season (seven times) or alternated with chlorothalonil.