Control of Alternaria Infection of Fruit of Apple Cultivar Nittany with Calcium Chloride and Fungicides. Alan R. Biggs, Associate Professor, University Experiment Farm, P.O. Box 609, Kearneysville, WV 25430. Morris Ingle, and W. D. Solihati. Professor, and Former Graduate Research Assistant, Division of Plant and Soil Sciences, West Virginia University, Morgantown 25606. Plant Dis. 77:976-980. Accepted for publication 21 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0976.

Calcium chloride (CaCl₂) was tested for its efficacy in reducing the incidence and severity of infection of the apple cultivar Nittany by Alternaria spp. In 1989, eight biweekly applications of flake (referred to as CaCl₂) or liquid CaCl₂ reduced the incidence of rot from 61% in the controls to 27 and 33%, respectively. Dip treatments alone reduced rot incidence to 17 and 12% for the CaCl₂ and liquid CaCl₂ treatments, and seasonal sprays followed by dip treatment reduced incidence to 5%. Nine CaCl₂ sprays, applied biweekly, reduced the incidence of the disease from approximately 44% in the controls to 12 and 18% in 1990 and 1991, respectively. Disease severity was reduced from 27 and 14 lesions per fruit in the controls to nine and six lesions per fruit in 1990 and 1991, respectively. In postharvest tests, fruit treated with CaCl₂ alone and in combination with iprodione exhibited the lowest incidence and severity of Alternaria rot after 3 and 6 mo in refrigerated storage. Best control of Alternaria rot was achieved with nine seasonal applications of CaCl₂ followed by a postharvest dip of CaCl₂ alone or in combination with iprodione. Fruit were sampled biweekly beginning in July through harvest to determine the frequency and pathogenicity of Alternaria spp. In 1991, isolation of epiphytic Alternaria spp. was uniform through the growing season, with isolation frequency of 52–72%. Isolation of Alternaria spp. from the same fruit that had been surface-disinfested yielded approximately 1–2% in July and increased gradually through the remainder of the season. At harvest, isolation frequency from surface-disinfested fruit averaged 34%. In 1992, isolation of epiphytic Alternaria spp. increased over the season from 22% in July to 69% at the end of September. Isolation of Alternaria spp. from surface-disinfested fruit was 2% in July and 11–16% in September.