Effect of Calcium Sulfate on Pod Rot of Peanut. A. B. Filonow, Assistant Professor, Department of Plant Pathology, Oklahoma State University, Stillwater 74078. H. A. Melouk, M. Martin, and J. Sherwood. Research Plant Pathologist, USDA-ARS, Oklahoma State University; Agricultural Scientist, Agricultural Chemicals Division, E. I. du Pont de Nemours & Co., Newark, DE 19714; and Associate Professor of Plant Pathology, Oklahoma State University. Plant Dis. 72:589-593. Accepted for publication 1 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0589.

Several experiments were conducted to assess the effectiveness of calcium sulfate (CaSO₄) in reducing the severity of pod rot of peanut cv. Early Bunch in Oklahoma. In the greenhouse, peanut pods were grown in soil naturally infested with Pythium myriotylum and Rhizoctonia solani (AG-4) or in steam-pasteurized soil artificially infested with P. myriotylum. In field microplots, peanut pods were grown in methyl bromide-fumigated soil artificially infested with P. myriotylum, R. solani, or both pathogens. Calcium sulfate as agricultural gypsum was applied before pegging at 0, 1,120, or 2,240 kg/ha. Plants in fields with histories of pod rot received up to 3,360 kg/ha CaSO₄. Hulls from CaSO₄-treated pods showed an increase (P = 0.05) in Ca content compared with hulls of nontreated pods. However, there was no decrease (P = 0.05) in pod rot severity in treated pods, nor were yields significantly (P = 0.05) increased in any experiment. There was no apparent relationship between Ca content in hulls and pod rot severity. Rot was induced in pods by adding P. myriotylum and/or R. solani (AG-4) to pasteurized or fumigated soils. These fungi were routinely recovered from CaSO₄-treated or nontreated pods grown in pathogen-infested soils, but rarely from pods grown in noninfested soils. Our results show the importance of specific fungal pathogens to pod rot etiology in Oklahoma and argue against a hypothesis suggesting Ca deficiency in hulls as the primary cause of peanut pod rot.