Diseases of tree bark cause oozing patches and dead sections of bark called cankers. These areas can occur on the limbs, branches and trunk of the affected tree. Insects and other diseases can attack the tree through the cankers, which can cause the tree to weaken or die. Few chemical treatments are effective for tree bark diseases.
Local county extension offices can provide assistance with identifying a disease. They can also take samples of healthy and diseased tissues for a laboratory analysis to determine the causal agent.
Eutypella parasitica fungus causes cankers on deciduous saplings or small trees. The cankers may contain black spores. A beige mat of fungal tissue grows under the affected bark. As thick callus tissue grows over infected tissue, the canker begins to resemble the back of a cobra's head. Larger cankers cause deformities in the limbs of affected trees. The wood under the canker is decayed and weakens the tree, which may break in strong winds.
Nectria Cinnabrina Cankers
The fungus Nectria cinnabrina causes elongated cankers on injured or weakened deciduous trees. Bright salmon pink fungal bodies followed by tiny red spores grow in diseased or dead bark. Affected areas may appear reddish from a distance due to the presence of the fungal bodies and spores, which is why the disease is also called coral spot Nectria. The spores turn into a slimy mass when wet and can be spread by water or insects. Nectria cinnabrina cankers can cause affected limbs and branches to die.
The fungus Fusarium circinnatum causes pitch cankers on the branches and trunks of pine trees. The slightly sunken cankers ooze heavy amounts of pitch and soak the wood underneath the bark, which remains on the canker.
Pruning off infected branches may prevent the spread of disease to other parts of the tree. Pitch cankers can slow and stunt the growth of trees. In some cases, they can girdle the trunk or exposed roots, killing the tree.
Long shallow cankers on smaller limbs of deciduous trees are caused by the fungus Valsa ambiens. Grayish to white spores that resembles pimples grow in the tissue of the canker. Infected trees usually do not die unless they are weakened by extremely cold temperatures or a long drought.