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Association of Wood Decay Fungi with Decline and Mortality of Apple Trees in Minnesota. D. R. Bergdahl, Associate Professor, Department of Forestry, University of Vermont, Burlington 05405. D. W. French, Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 69:887-890. Accepted for publication 2 March 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-887.

A 10-yr study of decline and mortality of apple trees in two orchards in Minnesota indicated that wood decay fungi were causal agents. A survey of 140 6-yr-old trees in 1972 showed 93% healthy, 6% declining (symptoms: papery or rough bark, cankers, dieback, and internal decay), and 1% dead and extensively decayed. Percentages for the same sample group in 1976 and 1982 were 54, 23, and 23 and 2, 19, and 79, respectively. Irpex tulipiferae was most common on cankered trees in both orchards. Field inoculations of healthy 3-yr-old Malus pumila ‘Connell Red’ confirmed that I. tulipiferae, Coriolus versicolor, and Schizophyllum commune could cause symptoms associated with decline and mortality of apple trees growing on less than optimal sites in Minnesota.