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Relationship Between Year of Infection, Tree Age, Tree Growth, and Nectria Canker of Black Walnut in Michigan. C. S. Thomas, Graduate Research Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. J. H. Hart, Professor, Departments of Botany and Plant Pathology and of Forestry, Michigan State University, East Lansing 48824. Plant Dis. 70:1121-1124. Accepted for publication 23 July 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-1121.

The occurrence of Nectria canker, caused by Nectria galligena, on black walnut trees (Juglans nigra) was studied in a mixed hardwood plantation established during 19451946 in southwestern Michigan. Diameter at breast height (dbh), number of cankers on the trunk from 0.3 to 3.7 m above ground, and canker shape (open or closed) were recorded for 2,718 trees. The number of cankers per tree was not correlated with dbh or canker shape (r = 0.23). Seven infected and four noninfected trees were harvested to determine tree growth rates. Chronological year and age of trunk section at the time of infection were determined for 200 cankers dissected from the seven infected trees. The number of infections per year (19611983) increased from 1961 to 1979, with peak infection years from 1978 to 1980. Most trunk sections were 1927 yr old when first infected, with peak infection ages at 22 and 24 yr. Tree growth rate was 30% less for black walnut trees with Nectria cankers than for healthy trees (P<0.01).