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Inonotus weirii

EPPO code



Inonotus weirii

Common names

English names: Laminated butt rot, yellow ring rot
Nordic names: Gul ringråd (DK)

Major host plants

Inonotus weirii could possibly infect many conifer species in Europe. The fungus has been identified in different ‘forms’ related to their respective hosts.


Inonotus weirii occurs in patches or centres of infection mostly as root rot. The disease can kill seedlings 1-2 years old, but the disease is usually not noticed before the stand reaches 10-20 years of age. Above ground, symptoms only become apparent when the root system is in an advanced stage of deterioration. Infected trees show reduced height growth, thinning of the foliage and sometimes a poor crop of smaller cones. Major roots decay and break close to the root collar. Wind-throw of living trees is common, even before crown symptoms are visible.

In advanced stages, the wood breaks down in a yellow, laminated, pitted rot. Brown, crust-like sporophores with a broad to narrow, white to cream, sterile margin may form on the underside of decayed stems and roots. In living trees, the infection will not usually extend more than 2-4 m up the trunk.

Inonotus weirii. Courtesy of EPPO

See more pictures on EPPO´s website


The disease is native in North America, Japan, China and far-east Russia.

A map can be downloaded from EPPO's website. See instructions here.


Infection occurs when roots of healthy trees grow in contact with infected roots. After initial contact with a living root, the mycelium grows on the bark, extending only 1-5 mm into the surrounding soil. The mycelium penetrates into the root tissue via healthy or injured bark. Although highly variable, the average annual radial extension of infection centres is about 20-40 cm. The fungus can persist in roots and stumps for 50 or more years. Sporophores are formed periodically on decayed wood, but spores are probably unimportant in spreading the disease. No conidia have been reported.

Major pathway(s)

Natural dispersal occurs slowly only over short root-to-root distances. Movement is most likely to occur by transport of infected coniferous logs or bark.

Detection and inspection

Observation with a hand lens will reveal characteristically long, brown setal hyphae between the laminated sheets of decayed wood. The fungus shall be identified in laboratory.

Pest status and importance

I. weirii causes a serious disease, affecting all trees between 6 years and rotation age, causing root decay leading to direct mortality or accelerated wind-throw. I. weirii is absent in the EPPO region, and establishment of the fungus could lead to substantial economic losses especially in Nordic countries.

Source of information

See further information here:

Author: Jorma Rautapää
Editor: Dorthe Vestergaard