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Rhizoctonia Leaf Spot of Flue-Cured Tobacco in North Carolina. H. D. Shew, Assistant Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. C. E. Main, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 69:901-903. Accepted for publication 6 May 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-901.

During the summer of 1984, a leaf spot disease not previously reported in the United States was observed on flue-cured tobacco throughout the area where the crop is grown in North Carolina. Symptoms began as small, circular, water-soaked spots that rapidly expanded into light green to tan lesions 26 cm in diameter with irregular margins. Tissue within the lesions was almost transparent, often displayed a pattern of concentric rings, and frequently dropped out leaving shot holes. Lesions, most common on lower leaves, were observed as high as 16 leaves (about 85 cm) up the stalk. Fungal mycelium was frequently present at the margins of lesions on the undersides of leaves, and occasionally, a hymenial layer and basidiospores of Thanatephorus cucumeris were observed. Rhizoctonia solani was isolated from these lesions and was shown to be the cause of them. The widespread occurrence and damage caused by the disease was attributed to the unusually cool, wet summer of 1984, which favored basidiospore formation and dissemination.