Epidemiology of Armillaria root disease in Douglas‐fir plantations in the cedar‐hemlock zone of the southern interior of British Columbia

Abstract

Results are presented from several studies on the epidemiology of Armillaria ostoyae in Douglas-fir plantations in the interior cedar-hemlock (ICH) biogeoclimatic zone of British Columbia. Two plantations were monitored for mortality by A. ostoyae and other agents for 35 years after establishment. In these and other plantations ranging in age from 7 to 32 years, one or more of the following factors were determined: source of inoculum, mode of spread and characteristics of lesions on roots of excavated trees; symptom expression in relation to tree age and damage to the root system and years from initial infection to death on trees killed by the fungus. Mortality from A. ostoyae began in both plantations about 5 years after planting, reaching 30% in one and 11% in the other after 35 years. The spatial pattern of mortality was similar to that reported from New Zealand, France and South Africa; however, the temporal pattern differed, beginning later and, instead of declining, continuing at a nearly constant rate to the present. To age 10, nearly all infections were initiated by rhizomorphs; as plantations aged, the proportion of infections occurring at root-root contacts increased. In seven plantations, in moist and wet subzones of the ICH, from 23 to 52% of Douglas-firs had root lesions, with the higher incidences occurring on moist sites. The occurrence of aboveground symptoms, reduced leader growth and basal resinosis, was related to the percentage of root length colonized by A. ostoyae on trees with more than 30% of root length killed. Average time from infection to death increased from 1 to 2 years at age 6 to 22 years at age 33. The outlook for timber yield from Douglas-fir plantations in the cedar-hemlock zone is discussed. Management alternatives for reducing damage from A. ostoyae when regenerating sites are reviewed.

Tree species selection revisited for plantations in the Interior Cedar Hemlock zone of southern British Columbia

“…The fungus is prominent throughout much of the ICH zone in the southern Interior and is known to pose a major threat to Douglas-fir in mature stands and to Douglas-fir and western larch in new plantations ). Annual mortality rates of 0.75% to 1.0% caused by Armillaria for Douglas-fir and western larch at EP 1153 are similar to those suggested by Morrison and Pellow (1994) and Morrison (2011). If these mortality rates continue, even for a few more years, the plantations of these species would be considered a failure.…”

Site, plot, and individual tree yield reduction of interior Douglas-fir associated with non-lethal infection by Armillaria root disease in southern British Columbia

“…Disease incidence is very low at this age (Morrison, 2009) and all trees were disease-free according to the root and root collar lesion dates. The Rosebery site with naturally regenerated trees initially grew more slowly, so that many trees took longer to reach 1.3 m; as a result, the onset of infection was delayed.…”

“…In Douglas-fir plantations, mortality caused by A. solidipes begins at about age 5, and its incidence increases slowly to about 1% per annum in older stands (Morrison, 2009). Work by Cruickshank (unpublished results) in fire-origin, 80-100-year-old seral stands dominated by Douglas-fir suggests that mortality also occurs throughout a rotation, but with increasing frequency after age 80.…”

“…Following harvest of similar sites, evidence of colonization by A. solidipes was found in 60-90% of stumps (Morrison et al, 2000Woods, 1994). The percentage of Douglas-fir infected in plantations also increases slowly, reaching 20-50% in stands aged 15-20 years in many habitats (Morrison, 2009). Disease epidemiology may be altered in managed stands by leaving stumps infected by A. solidipes, by planting, or by altering species mixtures (Cruickshank et al, 1997); hence the timing and magnitude of impacts could differ from those in natural stands.…”

Transcriptome of an Armillaria root disease pathogen reveals candidate genes involved in host substrate utilization at the host–pathogen interface

“…, ; Cruickshank ; Cruickshank et al. ; Morrison ). Thus, effective management strategies are needed to reduce the large impact of A. solidipes on diverse forest hosts across wide ranges of the Northern Hemisphere (Filip et al.…”