Effect of Wounding on Incidence of Black Rot of Cranberry in Wisconsin. M. R. Schwarz, Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706. D. M. Boone, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 69:225-227. Accepted for publication 1 September 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-225.

Laboratory trials showed that Ceuthospora lunata was primarily a wound-invading organism. Pycnidiospores germinated at a higher frequency on fruits that were wounded by puncturing the epidermis than on unwounded fruits kept at temperatures between 8 and 24 C. Black rot developed in more than 92% of cranberries wounded and dipped in a spore suspension. Control or bruised cranberries without a punctured epidermis showed little or no black rot. Cranberry leaf debris containing mature pycnidia of C. lunata was a principal source of black rot inoculum during the growing season and during wet-rake harvesting in October. Harvest water was an important medium for dissemination of C. lunata spores. Viable C. lunata spores at concentrations as high as 119/ml were found at harvest in flood waters used for wet-raking cranberries. Black rot developed in more than 46% of wounded cranberries immersed in harvest water samples, whereas no black rot developed in comparable cranberries immersed in heat-sterilized harvest water.