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Phytophthora cinnamomi as a Cause of Root Rot and Dieback of Cranberry in Massachusetts. F. L. Caruso, Cranberry Experiment Station, University of Massachusetts, East Wareham 02538. W. F. Wilcox, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Plant Dis. 74:664-667. Accepted for publication 26 February 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0664.

Cranberry beds in Massachusetts commonly exhibit areas of decline and dieback associated with low spots that accumulate excessive water. Affected plants typically are stunted, unproductive, off-color, and have poorly developed root systems; severely affected plants often die. When portions of beds with symptomatic vines are replanted with new vines, the replacement vines also usually die. Phytophthora cinnamomi was isolated from necrotic roots and under-ground runners of symptomatic plants in 215 different beds. When rooted cuttings of the cranberry cultivar Early Black were transplanted into potting mix artificially infested with individual isolates of P. cinnamomi, fresh weights of shoots and roots were reduced by 4888% and 8396%, respectively, compared with uninoculated controls. In similar tests involving a single isolate of P. cinnamomi, there were no significant differences in root or shoot fresh weights among inoculated and control plants of the cultivars Bergman, Franklin, and Stevens. In contrast, root and/or shoot weights were significantly lower for inoculated plants of the cultivars Crowley, Early Black, Howes, and Pilgrim, and plant mortality was particularly high for the cultivar Pilgrim. This is the first study documenting a species of Phytophthora as a pathogen of cranberry and the first to report the occurrence of P. cinnamomi in Massachusetts.