Ash Tree Bolete

We’ve been receiving multiple samples and questions about the Ash Tree Bolete.  We are proud to have Professor Emeritus Tom Weber from University of Nebraska – Omaha as an Extension Master Gardener share his insights with this particular fungi.

The first organism on the list of ash tree associates, good or evil, that pops up in most people’s minds is the emerald ash borer.  What would be number two?  Based on questions to the county extension office the “Ash Tree Bolete” (Boletinellus merulioides aka Gyrodon merulioides) is the clear number two.  As the name implies this mushroom is found on the ground under ash trees, both white and green ash.  It is common here in summer and fall.

As you can see in the photo, this mushroom has a cap that is brown on top and yellow on the underside, which is covered with angular tubes rather than the gills more commonly seen on mushrooms. The caps are typically two to six inches across. The short, stubby, off-center stem often results in clusters of this mushroom hidden in the grass.

The vegetative part of the fungus, the mycelium, is associated with the roots of the ash tree in a symbiotic relationship.  The fungus obtains carbohydrates from the tree and in turn helps the tree roots absorb nutrients from the soil.  The Ash Tree Bolete also has a relationship with the leafcurl ash aphid.  The mycelium forms little knots of tissue that surround and protect the aphid and in exchange the fungus gets nutrients from the aphid’s honeydew.

Is the Ash Tree Bolete edible you ask?  The answer is a bit complicated.  In mushroom ID books you will see it rated as edible, edible but not recommended, edible but not desirable, bad, etc.  It does not produce a toxin, so in that sense it is edible.  Descriptions of taste also vary tremendously from mild to acidic and unpleasant with a peculiar consistency.  Some say removing the tube layer helps make them more palatable.  Michael Kuo, in his book 100 Edible Mushrooms says “No amount of cleaning, drying, or seasoning will do anything to cover this mushroom’s uncanny resemblance to a Brillo pad.  …  The spongy consistency, the dirty-metal taste of it, and even the odd aftertaste it leaves in your mouth …” strongly suggests that the Ash Tree Bolete may not be a mushroom you want to sample.

If the presence of the Ash Tree Bolete in your lawn bothers you, just picking and tossing the mushrooms out is the best solution.  Fungicide applications will have little effect.

Scott Evans
Scott Evans is a horticulture assistant with Nebraska Extension in Douglas-Sarpy Counties. A certified arborist through International Society of Arboirculture and Nebraska Arborist Association. Scott is also Tree Risk Assessment Qualified through ISA. Scott co-leads the Master Gardener program in Douglas & Sarpy counties. Along with volunteer management he provides his expertise with disease and insect identification, lawn and landscape weed management, plant health, and I.P.M. practices. He also enjoys growing many houseplants ranging from African violets to cacti and succulents. Scott has two Bachelors of Science, one in Biology (emphasis in Botany, Ecology and Environmental Science) and second in Environmental Geology from Northwest Missouri State University. He earned his Master of Agriculture from the University of Nebraska-Lincoln.

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