Root Rot and Chlorosis of Released and Thinned Western Redcedar

Western redcedar (Thuja plicata Donn) trees, released and thinned in 1940, had root rot and chlorosis 20 years later. Armillaria mellea was the most frequently isolated root pathogen, followed by Corticium galactinum, Poria weirii, and Fomes annosus. The fungi were not confined to roots but formed basal cankers and caused minor butt rot. Rotted roots were more frequent and the root rot and basal cankers were more extensive on released than on nonreleased trees. Released trees also had marked chlorosis and resinosis. These symptoms appeared to be independent of root rot, since nonreleased trees with root rot did not display these symptoms and released trees with little or no detectable root rot did. As few trees on released plots were free from root rot, the cause of the chlorosis and resinosis could not be definitely determined; these symptoms could have been due to release alone, to an interaction of root rot and release, or to toxin production by the fungi.