Pholiota / Yellow-Cap Fungus

There was no notable Pholiota disease activity this year. Pholiota spp. were detected at only two locations near Anchorage in 2024, compared to 16 ground detections in 2023. No research grade observations of Pholiota were submitted to iNaturalist this year.

Many Pholiota occurrences have been mapped on aspen, birch, black spruce, and willow in Southcentral and Interior Alaska (see Detection Map) but most have not been identified to species. Pholiota mushrooms are most common at the base of trembling aspen, but usually these trees have no symptoms until they uproot or snap near the root collar. Mushrooms collected from  live Sitka spruce and western hemlock trees near Juneau were molecularly confirmed to be Pholiota (99% sequence match to Pholiota aurivella) in 2020.

The fruiting body is an annual mushroom, typically produced in clusters. The fungus is called the yellow-cap fungus or the scaly-cap mushroom. The upper surface of the mushroom cap is yellow-brown and usually scaly and/or sticky. Young specimens may be flagrantly scaly while older specimens may become sticky and lose their scales. Gills on the lower surface are yellow at first, later turning brown. The stem (i.e., stipe) may or may not have a ring and may be scaly. Mushrooms may develop at the base of the tree or on the stem, particularly at wounds. Incipient wood decay appears as light yellowish areas in the heartwood. Wood with advanced decay is yellow-white with yellow or yellow-brown streaks. Thin strands of yellow-brown mycelium, occur along the grain. If the strands of mycelium are pulled from the wood, irregular channels, resembling insect tunnels, remain.

Pholiota species cause a white rot of wood in live trees, typically invading through wounds. Mushrooms on a living tree indicate extensive decay. Some species are root rot fungi while others cause stem decay. Several Pholiota species have been reported to cause butt and trunk rot of trembling aspen throughout its range in North America. There are many species of Pholiota found in Alaska, only some are capable of decaying live trees. For exact determination of any specific specimen, a key for Pholiota must be used (available here). Managers can reduce effects of wood decay fungi by limiting tree ages through shorter rotations and by reducing trunk wounds. 

Smith, Alexander H.; Hesler, L. R. 1968. The North American species of Pholiota. New York, NY: Hafner Publishing Company. 349 p. Available here.