Hypoxylon Canker of Oaks

The Texas Hill Country is known for its beautiful live oak, red oak and even post oak and blackjack oak species. These trees seem to thrive here with little trouble except from people and nature. People affect these trees by building houses, driveways or yards around these fine trees and nature affects them by the drought we are currently in now. Droughts put these trees under significant stress and this stress sets the tree up for the possibility of disease infection. Besides oak wilt we have another problem disease of these oaks called Hypoxylon canker caused by the disease organism Hypoxylon atropunctatum. This disease is found everywhere in abundance but it is not a problem for healthy trees. Stressed trees unfortunately are susceptible to this fungus through wounds and then the disease grows easily in the sapwood. The first symptoms are yellowing and wilting of leaves, and death of top branches of the tree. The fungus is capable of spreading over 3 feet in all directions in a single year from the infection point. Hypoxylon canker is characterized by the large pieces of bark that fall from the tree as it dies because the disease works on the cambium layers that hold the bark in place. Underneath the bark are the fruiting structures of the fungus that are dusty brown spores. These blow from tree to tree to spread the disease further to weak, drought stressed trees.
Before you think all your oaks are going to die please be assured that this disease is not that widespread in our beautiful oaks but it is more of a problem in droughts. Watering all trees but especially oaks in our landscapes a little more this summer will help prevent the stress and consequently the disease.