Incidence of Heterobasidion annosum in Mixed-Conifer Natural Regeneration Surrounding Large True Fir Stumps 20-25 Years after Harvesting in Northeastern Oregon

High-elevation true fir stands on federal lands have a long history of selective harvesting. In 1989 a high frequency (89%) of Heterobasidion annosum, the cause of annosus root disease, was found in residual true fir stumps (mean, 20-in. diameter) cut 5-9 years earlier in northeast Oregon. In 2004, H. annosum was found at the stump surface of 29% of the natural conifer regeneration (mean, 18 years) within 20 ft of infected residual stumps. A total of 16 of 122 (13%) live saplings had H. annosum-caused stain or decay. Only 3% of 126 sample trees, however, were dead and infected by H. annosum. Infection was confirmed in 62% of decayed trees, 33% of stained trees, and 22% of trees with no visible stain or decay at the stump surface. Only 3 of 122 living saplings showed typical root disease crown symptoms (chlorosis), but only one of these had H. annosum. Only 1 of 16 live saplings with H. annosum-caused stain or decay was chlorotic. Incidence of infection was 44% in Engelmann spruce (7 of 16 trees), 31% in Douglas-fir (5 of 16 trees), 31% in subalpine fir (4 of 13 trees), and 27% in grand fir (21 of 77 trees). The S-type of H. annosum was confirmed in a sampled grand fir. There were no significant differences between H. annosum-infected and apparently healthy trees regarding live crown ratio and distance from infected residual stumps. Infected trees, however, were significantly (P = 0.025) larger in diameter than apparently healthy trees. The dynamics of H. annosum infection in spruce and Douglas-fir in northeast Oregon are discussed as well as treating true fir stumps with boron-containing products to prevent stump infection by H. annosum.