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Tuesday - November 29, 2011

From: Dripping Springs, TX
Region: Southwest
Topic: Diseases and Disorders, Trees
Title: Large oak with possible Laetiporus fungus
Answered by: Nan Hampton

QUESTION:

We have a huge oak tree in front of our new house. After the first rain this fall a large fungal growth appeared in an old knothole of the tree and I would guess that it is Laetiporus. A neighborhood street was cut just outside of the tree drip line in the last 7-10 years. Construction traffic also recently occurred on the lot, but again outside of the tree's drip line as we fenced off this tree and were very careful of it. Other than that, the tree appears to be very healthy. We watered it some toward the end of this summer, but even without that it looked the healthiest of all the trees throughout this drought. Should we treat the tree in some way to kill this fungus?

ANSWER:

The University of California Davis Integrated Pest Management (IPM) has an article, Wood Decay Fungi in Landscape Trees, that describes (with photos of the fruiting bodies) several types of fungi that grow in and on trees. If your tree really does have the Laetiporus sp., the conks (fruiting bodies) showing on the outside of the tree indicate that there is probably extensive internal damage and that the fungus mycelia have been growing inside for many years. As Michael Kuo says about Laetiporus sulphureus (The Chicken of the Woods):

"The mushrooms do not appear until well after the fungus has attacked the tree; by the time the chickens appear, they are definitely coming home to roost, as far as the tree's health is concerned."

And, from Disease Recommendations for Trees and Shrubs from the University of Michigan Extension Service:

"Fungus invades the roots, trunk and butt of tree through wounds causing a brown cubical rot. First evidence may be the production of a fleshy, yellow shelf fungus on the trunk. However, presence of the fungus suggests considerable rot within and possibility of a hazard tree should be investigated."