Question
I have several post oaks on my property. The bark on many of them is turning white looking like ash. The bark is real soft where this is occouring. What exactly is causing this problem? Will these trees die soon? Is there anything I can do to cure the problem?

Answer
Sounds like Hypoxylon canker.

The most obvious early symptom of Hypoxylon is the sloughing off of bark. The bark falls or peels off to expose a dusty- looking brown canker. This early stage of the canker is an active stroma,which bears brown masses called conidia. The one-celled conidia are scattered by the wind and can cause infection to other trees. The active canker soon hardens, changing color to silver or grey and as the sexual stage progresses, begins to produce black spores.
These spores can be spread by rain or insect activity to other branches of the same tree or to other individual trees. Cankers can easily spread 3 feet in one season of growth. Large  Oak trees can die within one or two years of displaying symptoms of infection.

There is no legitimate or effective control for Hypoxylon Canker. The fungus remains active on dead wood, so infected or suspect wood should never be kept or stored. Infected limbs or stems can be pruned out, but use good judgement based on percentage of unaffected canopy. Even after pruning, there is a likelihood of canker spread
and dieback. Trees that have not lost more than 10-15 percent of canopy would benefit from supplemental watering in dry conditions and aeration/fertilization. Avoid root injury and monitor trees closely that have been impacted by construction, soil
compaction or drought stress. It is possible that this fungus could enter fresh pruning cuts and or injury by climbing spikes and could be spread from spikes or pruning tools. Dormant pruning is the
safest way to go on Oak trees.

Trees with extensive Hypoxylon infections are usually beyond repair. Removal of severely infected trees to reduce local sources of inoculum (i.e., infectious spores) is recommended. Careful pruning of branches that have localized infections should help prevent advancement of the fungus within the infected trees. Prevention of infections through avoiding wounds, root damage, etc., and providing adequate moisture via irrigation to susceptible trees during prolonged periods of dry weather is the best method of control. The presence of Hypoxylon cankers is usually an indicator of severe stress and often a warning to take precautions to reduce stresses (if they can be identified and reduced) affecting nearby trees of the same species.


Here is a web link to information on Hypoxylon cankers

http://easttexasgardening.tamu.edu/Homegardens/hypoxylon.html