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.

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.  The hypoxylon fungus is  weak pathogen in that  is not aggressive enough to invade healthy trees.

Hypoxylon canker  usually increases when prolonged drought occurslike we have had in Houston.  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 normal moisture content.  However if the  tree is weaken or stressed,  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.