Fungus on oak Trees #167603 - Ask Extension


Fungus on oak Trees #167603

Asked February 21, 2014, 10:11 AM EST

We have a a-lot of oak trees in our woods area, they have a black looking fungus on them, then the bark falls off,  it did not shed its leaves this fall or winter and the trees seem to die quick, it seems like its spreading,  we have lost at least 30 trees some young and some mature, how can we stop this?

Johnson County Texas

Expert Response

From your description my best guess is Hypoxylon canker.  Hypoxylon canker is a fungus that causes cankers and death of oak and other hardwood trees.  The disease is common in East Texas and all across the southern United States.  Relatively healthy trees are not invaded by the fungus, but the hypoxylon fungus will readily infect the sapwood of a tree that has been damaged, stressed, or weakened.  Natural and man-caused factors that can weaken a tree include defoliation by insects or leaf fungi, saturated soil, fill dirt, soil compaction, excavation in the root zone of the tree, removal of top soil under the tree, disease, herbicide injury, drought, heat, nutrient deficiencies, competition or overcrowding, and other factors.  The hypoxylon fungus is considered a weak pathogen in that it is not aggressive enough to invade healthy trees.  In addition to the hypoxylon fungus, weakened and stressed trees may become susceptible to a host of other insect and disease pests.     Hypoxylon canker activity usually increases when prolonged drought occurs.  When drought stresses trees, the fungus is able to take advantage of these weakened trees.  The moisture content of living wood in live, healthy trees is typically 120% - 160%.  It is difficult for hypoxylon canker to develop in wood that has a normal moisture content.  However, any of the factors listed above could weaken or stress trees causing the moisture content of the wood to reach levels low enough for the hypoxylon fungus to develop.  When this happens, the fungus becomes active in the tree and invades and decays the sapwood causing the tree to die.  Once hypoxylon actively infects a tree, the tree will likely die.     An early indication that hypoxylon canker may be invading a tree is a noticeable thinning of the crown.  Also, the crown may exhibit branch dieback.  As the fungus develops, small sections of bark will slough from the trunk and branches and collect at the base of the tree.  Where the bark has sloughed off, tan, olive green, or reddish-brown, powdery spores can be seen.  Different tree species that are infected with hypoxylon canker will produce the different colors of spores.  By the time the spores become visible, the tree is dead.  In four to eight weeks, these tan areas will turn dark brown to black and become hard.  They have the appearance of solidified tar.  After several months, the areas will become a silver-gray color.     Once the fungus invades the tree, the sapwood begins to rapidly decay.  Dark decay lines can be seen running through the wood.  Trees that have died from hypoxylon canker and are located in an area where they could fall on structures, roads, fences, powerlines, etc., should be removed as soon as possible.     There is no known control for hypoxylon canker other than maintaining tree vigor.   
Zach Davis Replied February 25, 2014, 4:16 PM EST

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