Fungus Infections of Trees are Often Fatal

Fungi on trees may indicate infection

Brian Jervis: Ask a Master Gardener

Saturday, January 23, 2016

Q: There are mushrooms growing from the bark of my oak tree. What should I do about this? Gene, Tulsa

A: Mushrooms are a part of a fungus, which is used for reproduction called a “fruiting body.” It is usually only a small part of the overall fungus. These may be on trunks, limbs or extend up from underground roots. Some have the usual mushroom shape, while others form a saucer-like structure extending from the bark. These are often referred to as “conchs” or shelf fungi.

When present on the trunk of a tree, or on the roots of a tree, it implies that the tree has a significant infection, which most often is fatal. Generally, there is no chemical treatment effective for an infection such as this. Good general care of the tree in terms of water and nutrition is the only recommendation.

The usual story is of the tree having experienced a wound due to weather damage, lawn equipment and root damage related to excavation or severe stress due to environmental factors such as drought.

With the right condition and the right fungus, an infection can occur. Fungi have chemicals that are able to break down and feed on the wood, eventually causing a generalized infection. Most trees die of this, but it may take a few years.

As the infection spreads, evidence of general decline in the tree may be seen. Leaves are smaller and annual stem growth is shortened. Leaves often turn fall colors and drop prematurely in the fall. As the infection spreads, the limbs in the top of the tree usually die first. Later, supporting structure of limbs, trunk and roots are greatly weakened. They then become a hazard to you and your property when a wind storm develops.

It is best to start thinking about the removal and replacement of a tree once mushrooms develop and tree decline is observed. This should be done by an ISA-certified arborist. A list of those certified in our area may be found on the website treesaregood.com.

There is a common fungal infection of trees in our area that is worth mentioning. It is called hypoxylon canker (HC). It occurs especially in oaks but may infect many others.

HC is unlike other fungi in that heat and drought stress allows it to infect oaks. This type of stress reduces immunity and the fungus, which is normally wide-spread in nature, invades the tree. The terrible hot and dry summers we had in 2011-12 caused enough stress that many oaks developed this disease.

This fungus does not produce mushrooms, but it does produce massive amounts of grey to brown to black spores, which lift bark from the trees. The first indication that HC is present is often loose bark and powdery residue. When this is found in oaks, or any tree, considerations for removal of the tree should be made.

Garden tips

§  Even though there may be adequate moisture in the ground, it is normal for evergreen broadleaved shrubs to appear “wilted” during extreme cold. This is rapidly reversible after the temperatures warm. This is a way some plants have in dealing with the cold.

§  Try to keep fallen leaves off newly seeded fescue. Fescue is capable of growing roots in winter unless the ground gets extremely cold. A good root system will help fescue to better tolerate the heat next summer. To grow roots, the grass needs sunlight.