Abstract The percentage of infection and the rate of decay in inoculated white spruce trees were greater for Coniophora puteana (Schum. ex Fr.) Karst. than for Polyporus tomentosus Fr. No correlation was found between the rate of decay by either fungus and the heartwood moisture content. Coniophora puteana decayed wood significantly faster and caused more infections in trees that died during the 3 year incubation period, than in those that remained alive. C. puteana overran and decayed P. tomentosus inoculum blocks in adjacent inoculations. Some inoculated trees remained uninfected. Heartwood moisture contents were not increased by irrigation but were decreased by severing roots and covering soil around the base of trees with plastic sheeting.