Garden Detective

This fungus signals trouble

What's this weird-looking fungus growing out of an acacia tree on Ken Smith’s property in Folsom? It's commonly called artist's conk, and it's not pretty.
What's this weird-looking fungus growing out of an acacia tree on Ken Smith’s property in Folsom? It's commonly called artist's conk, and it's not pretty.

Q: I have noticed that I have a large fungus growing on the base of my blackwood acacia. The tree is about 11 years old and is 18 inches at the base, and about 30 feet tall and wide. I have not noticed any issues with the tree as of yet, but am worried about this newish fungal growth. I have not been able to find this specific growth online, so I am not sure if it might be “Ammillari” fungus or not. I know the fungus growth is relatively new as I had placed a new plant near the tree that got its fronds stuck in the white section of the growth.

There is only one such protrusion from the trunk at the base of the tree and it is about 4 inches in depth (trunk to outside) and about 6 inches across of widest point. It also extends downward into a small hallow in the tree. I am currently worried it might destroy the tree and would like to know your opinions and anyway to take care of this. I have resisted so far to taking the fungus out but would like your input.

Ken Smith, Folsom

A: Based on the photographs you provided, your acacia tree appears to have been invaded by Ganoderma applanatum, commonly known as artist’s conk, according to UC master gardener Rachel Tooker.

This is a fungus that is found in a wide variety of landscape and forest trees, including acacia, alder, ash, birch, citrus, elm, eucalyptus, fir, magnolia, maple, mulberry, oak, pepper tree, pine, poplar, sweet gum, sycamore, tulip tree and willow. The fungus reproduces by airborne spores. It can also spread through root grafting.

The first visible sign of infection is often the formation of semi-circular, fan-shaped fruiting bodies – called “conks” – at the base of the tree. The conks can range in size from 2 to 30 inches wide and 1 to 8 inches thick. Typically, the conks are found near ground level, but columns of decaying wood can extend as far as 15 feet above and below the visible conk.

The upper surface of conks are brown and the lower surface is white. The fungus gets its name because the white undersurface can be written on or scratched. These abrasions then turn dark brown. Artists have used this habit to make a variety of decorative items.

The fungus invades trees through wounds and causes white rot of the sapwood and heartwood in roots and trunks. Unfortunately, by the time the fruiting body becomes visible, it is too late to reverse the infection.

Removing the conk will not slow the rate of decay. It will continue to progress through the tree and form new fruiting bodies.

Depending on the overall health of the tree, the decay can progress quickly, significantly reducing wood strength and making the tree quite hazardous. Trunks and limbs will become unable to support their own weight and can fall with little to no warning, especially when stressed by wind, heavy rain, or other conditions.

If you observe a conk on a tree in your home landscape, you may want to have your tree inspected by a licensed arborist who can determine if the tree is hazardous and my need to be trimmed, cabled, braced or removed.

For more information, consult UC IPM Pest Note, Wood Decay Fungi in Landscape Trees, Publication 74109, which can be downloaded at

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