Hypoxylon canker is caused by an opportunistic fungi, (hypoxylon antropunctatum) attacking primarily drought stressed trees and it will finish the kill. Hypoxylon is unable to cause disease in healthy trees but is quick to colonize weakened or dying bark and wood. Hypoxylon canker is a fungus that causes cankers and death of oak and other hardwood trees. The disease is common in here in Texas Hill Country, 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. Hypoxylon canker is a tree disease appearing as a necrotic (dead) lesion on limbs, branches and trunks of affected trees.