Because oak trees are usually shade trees, when they get distressed, they become susceptible to the oak disease, hypoxylon canker. The specific species of this fungus is called Hypoxylon atropunctatum. It’s common in Texas due to the fact that Live Oak, Red Oak, Blackjack Oak and Post Oak are common types of trees that make up a significant portion of the urban tree population. It appears on trees that are easily stressed or intolerant to environmental changes.
The disease first shows up as a light brown or tan area that is dry or dusty when disturbed. This is called the asexual phase of the hypoxylon canker. These are the spores of the fungus. They can travel far distances in wind-driven currents. When these infections first develop, the bark becomes paper thin on the surface of the cankers and flakes off, exposing a brown fungal patch. Within a few weeks, the light brown dusty area turns a silvery-gray color with scattered black spots – we call this the sexual stage. The canker, at this point, is hard to the touch.
Hypoxylon atropunctatum is generally a weak parasite and will cause no problems to healthy trees. The tree can defend itself from the canker with normal defense mechanisms. The canker appears rapidly on the exterior of weak or dead limbs. The organism lives harmlessly in the outer bark tissue and aids the tree in quickly shedding or discarding the limbs. If the hypoxylon canker appears on limbs or branches, it’s not considered lethal. It’s often removed by getting rid of the dying or dead limbs.
When the disease appears on the main trunk or the stem of a tree, then the tree is dying or nearly dead. It is rare for a tree to recover from hypoxylon canker if it appears on the trunk or stem. Why? The main trunk carries moisture and nutrients up the tree. The outer layer of the trunk, under the bark, is only a few cell layers thick and constitutes a tree’s current growth ring. The canker on this part of the tree means that there’s something seriously wrong with the main transport system. The tree is not able to sustain itself and dies.
Hypoxylon canker does not spread from tree to tree as is commonly believed. The fungus already lives in the outer bark of most healthy Oak trees. It should be noted that any portion of a tree where Hypoxylon Canker appears, the wood will dry out quickly. It becomes brittle and dangerous.
There is really no cure for Hypoxylon Canker. Removing dead and weak limbs, as well as maintaining overall tree health, will be the best way to deal with the problem. You should make sure that you’re doing the following to avoid this problem from getting out of hand:
- Regularly and aggressively provide deep root fertilization for your tree.
- Prune trees to eliminate any weak, dying or dead limbs.
- Avoid injury to the trunk and limbs of the tree.
- Avoid reductions or additions of soil in a tree’s root zone. This keeps the bark tissue from breaking down.
If you suspect your tree has Hypoxylon Canker, please contact us at 512-341-8888. We will be happy to help treat your tree. Remember, we don’t diagnose tree diseases, but we can prune and help improve the health of your tree.