VIEW ARTICLE

Disease Control and Pest Management

Sclerotinia Blight of Peanut: Relationship Between in vitro Resistance and Field Efficacy of Dicarboximide Fungicides. T. B. Brenneman, Former graduate research assistant, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Tidewater Research Center, Suffolk 23437, Present address: Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793; P. M. Phipps(2), and R. J. Stipes(3). (2)Associate professor of plant pathology, Virginia Polytechnic Institute and State University, Tidewater Research Center, Suffolk 23437; (3)Professor of plant pathology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Phytopathology 77:1028-1032. Accepted for publication 8 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1028.

Two isolates of Sclerotinia minor with in vitro resistance to iprodione and vinclozolin were pathogenic to peanut in field microplots and survived as well as a fungicide-sensitive field isolate. Dicloran, iprodione, and vinclozolin were applied to peanut plants for 3 yr at annual rates of 8.41, 3.36, and 2.52 kg/ha to control Sclerotinia blight. Disease caused by in vitro fungicide-resistant isolates was suppressed 19, 33, and 87% by dicloran, iprodione, and vinclozolin, respectively, compared with 15, 24, and 76% for the sensitive isolate. Isolates recovered from tissue samples still grew on fungicide-amended media, indicating that in vitro resistance and in vivo resistance were not equivalent. Fungicide treatments reduced sclerotial populations of all isolates in soil and reduced the viability of sclerotia recovered from plots infested with sensitive isolates but not from those infested with resistant isolates. Nine isolates of S. minor with in vitro resistance to iprodione or vinclozolin were found to have cross-resistance to these fungicides as well as to dicloran and pentachloronitrobenzene. This work illustrates the potential risks associated with in vitro evaluation of fungicide resistance and suggests that the threat of dicarboximide resistance in S. minor may not be as great as originally-thought, since disease control is still achieved under field conditions.