What is this mushroom on my tree? Is it harmful?

Julie Hudak’s oak tree has a yellow fungus-looking growth at the base of the tree. It’s about 10 years old and its companion tree doesn’t seem to have the same problems. Previously she’s seen mushrooms growing out of the base where the mulch and the oak tree touch. Is this a problem?

While many fungi and other microbes in the garden aren’t worrisome, unfortunately, this one is. April Rose, Urban Forest Health Coordinator for the City of Austin, tells us: “There are fungi that are just normal leaf spots and no big deal, as well as fungal bodies that grow on dead tissue that is localized (like an old pruning wound) vs. spreading root rots like ganoderma, like shelf fungus.”

The organic matter around the base of this tree is great mulch, but it’s touching the tree, which isn’t good. Also, it appears as if the tree was planted too deeply.

Fungal growths such as these, at the base of the tree, are known as shelf fungi, and they indicate a tree in decline.

Another red flag here is all the leaves sprouting from low on the trunk; an indicator that the tree is stressed and trying to grow from any possible place in order to survive. This tree is struggling for numerous environmental reasons, so it’s more susceptible to invasion by pests.

I’d recommend having a certified arborist take a look at the tree, to determine its overall health, and to see if there’s anything that can be done. But shelf fungi are not something that can be treated, so most likely, the tree will need to be replaced.