Annosus/Heterobasidion Root & Butt Rot

Heterobasidion occidentale conk on Sitka spruce.
Heterobasidion occidentale conk at the base of Sitka spruce.

Heterobasidion occidentale sp. nov. Otrosina & Garbelotto

Heterobasidion occidentale (formerly known as the spruce-type of  Heterobasidion annosum) causes root and butt rot in old-growth western hemlock and Sitka spruce forests in Southeast Alaska. In conjunction with the change of the pathogen name, the disease name has changed to Heterobasidion root and butt rot.

Disease Impacts & Forest Management

This pathogen does not typically kill trees. In Alaska, it has only been detected in Southeast Alaska, where disease incidence and severity are apparently unaffected by management activities. Elsewhere in the world, spores of the fungus are known to readily infect fresh stump surfaces, such as those found in clearcuts or thinned stands prompting management intervention.

Stringy white rot decay of Heterbasidion occidentale.
Stringy white rot decay of Heterbasidion occidentale.

Studies in managed stands in Southeast Alaska indicate limited stump infection and survival of the fungus. Reasons for limited stump infection may be related to high rainfall and low temperatures in Alaska’s coastal forests hindering infection by spores. It has also been proposed that other fungi, such as Armillaria species, are antagonistic to Heterobasidion occidentale in Alaska. The high rate of heart rot in old-growth hemlock that was attributed to H. annosum by Kimmey in 1956 by examining the appearance of wood decay should probably be reevaluated using modern genetic methods.

Links & Resources

Heterobasidion occidentale factsheet from Natural Resources Canada. Available here

Annosus Root Disease of Western Conifers Forest Insect Disease Leaflet 172, revised 2000. Available here.

Table 4 from Kimmey 1956 with fungal decays of conifer hosts in SE Alaska
Table 4 from Kimmey 1956 showing the relative contribution
of decay fungi to decay incidence. Heterobasidion occidentale
is listed as Fomes annosus.

Shaw III, Charles G. 1989. Is Heterobasidion annosum Poorly Adapted to Incite Disease in Cool, Wet Environments? In: Otrosina, William J.; Scharpf, Robert F., technical coordinators. 1989. Proceedings of the symposium on research and management of annosus root disease (Heterobasidion annosum) in western North America; April 18-21, 1989; Monterey, CA. Gen. Tech. Rep. PSW-GTR-116. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; p.101-104. Available here.

Content compiled by Southeast Alaska Forest Pathologist Robin Mulvey, robin.mulvey@usda.gov.
 

Contact us    Forest Health Protection Homepag