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Velvet-Top Fungus/Cowpie Fungus/Dyer's Polypore (Phaeolus schweinitzii)

Trees Affected

Common: Most conifers, notably Douglas fir and Sitka spruce along the coast

Summary

Phaeolus schweinitizii Fresh Fruiting Body. Source: American Mycological Association
Phaeolus schweinitzii is a widespread fungus that causes heart rot in many conifers and plays an important role in maintaining soil quality. The spores of this pathogen enter trees through fine root tips in the soil, growing into progressively larger roots and eventually into the main stem of its host tree. Since Phaeolus schweinitzii is confined to heartwood, it does not directly affect tree vigor, but does affect its host’s structural integrity. Despite its potential for creating hazard trees, this fungus is also an important part of the ecosystems it inhabits, since the kind of decay it leaves behind contributes to soil conditions that promote conifer root health and nutrient acquisition. Signs and symptoms of this fungus include layered, cushion-like yellow to brown fruiting bodies, trunk swelling near the base of the tree, and cubical brown rot in the heartwood. Although this fungus can infect trees of any age, extensive decay is primarily associated with older trees.

Local Distribution

Widespread across region.

Management Strategies

Avoiding root injury can somewhat reduce the likelihood of infection with Phaeolus schweinitzii. However, given how common this fungus is across the northern hemisphere and given that it serves an important ecological function, total avoidance is both unlikely and undesirable. However, the structural damage caused by Phaeolus schweinitzii can be estimated by coring the tree and assessing how much brown rot is present within the bole. If the affected tree is in an area with significant human traffic, removal may be necessary for public safety. If the affected tree is in an area where it is unlikely to damage property or people, management strategies include shorter harvest rotations for timber, or taking no action and recognizing that this fungus has an overall positive impact on forest health.

Pests and Pathogens with Similar Symptoms

Fomitopsis pinicola: This fungus also produces a cubical brown rot, but enters through aboveground wounds. Fomitopsis pinicola fruiting bodies are perennial conks with a smooth white underside and a reddish-brown top.

Laricifomes officinalis: This fungus produces a cubical brown rot, but enters through branch stubs much higher up on the tree. The fruiting bodies of Laricifomes officinalis are perennial light-colored hoof-shaped conks, often located at the base of branch stubs high up on the trunks of old-growth conifers.

Further Reading

Disease description, management, and additional resources:

https://www.caforestpestcouncil.org/root-diseases