Control of Sclerotinia Blight of Peanut: Sensitivity and Resistance of Sclerotinia minor to Vinclozolin, Iprodione, Dicloran, and PCNB. T. B. Brenneman, Graduate Research Assistant, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg 24061. P. M. Phipps, and R. J. Stipes. Associate Professor of Plant Pathology, and Professor of Plant Pathology, Virginia Polytechnic Institute and State University, Tidewater Research Center, Suffolk 23437, Virginia Polytechnic Institute and State University, Blacksburg 24061. Plant Dis. 71:87-90. Accepted for publication 19 June 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0087.

Five isolates of Sclerotinia minor from different peanut fields were evaluated for sensitivity to dicloran, iprodione, PCNB, and vinclozolin. Tests were conducted with fungicide-amended glucose yeast-extract agar (GYEA). ED₅₀ values showed vinclozolin (0.07 µg/ml) to be the most inhibitory, followed by iprodione (0.11 µg/ml), dicloran (0.91 µg/ml), and PCNB (1.27 µg/ml). ED₅₀ concentrations of vinclozolin suppressed sclerotium production, whereas iprodione and dicloran increased it compared with GYEA alone. Sclerotial size increased significantly in the presence of ED₅₀ concentrations of dicloran and vinclozolin. Nine strains of S. minor were isolated from fungicide-resistant growth sectors on GYEA amended with either iprodione or vinclozolin but not dicloran or PCNB. All resistant strains were capable of growth at up to 1,000 µg/ml of iprodione or vinclozolin. Eight of these retained resistance for 23 mo when repeatedly cultured on unamended GYEA. After 36 mo, only seven strains were resistant to fungicides. A total of 763 isolates from plants in fields treated with these fungicides were tested over 3 yr, and no resistance was found. All four products significantly increased peanut yield and value in replicated field trials. Disease incidence at harvest was reduced by an average of 37.1, 41.6, 49.0, and 72.0% by PCNB, dicloran, iprodione, and vinclozolin, respectively, over a 3-yr period.