Internal brown spot (IBS) was found consistently in the `Atlantic' cultivar at Lexington in 1967, 1968 and 1989, and at Owensboro and Quicksand, KY in 1987, Treatments of foliar and soil applied CaSO4 in 1987, soil-applied CaSO4 in 1988, and straw mulching in 1989 did not reduce IBS. Irrigation increased IBS because of larger tubers and increased Ca content of plants as compared with non-irrigated plants. Tubers showing IBS had higher Ca content in affected tissue than in non-affected tissue. Both IBS and Ca content of leaves increased as the plants aged.
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