Question
Hello,and thanks so much for taking my question.  I have a pin oak trunk size about 35" dia.  I found a small hole about 3 ft off the ground.  The hole is about 2" dia, it was ozzing what I think is slime flux...foamy and yeast oder.  I cleaned out the hole and the ozzing is slowing down some.  Should I just leave the hole alone?  And if the ozzing does stop should I fill the hole? I am worred bugs will bore in the hole?  Thanks for you time.

JOE

Answer
Slime flux is a common problem on oaks and that sounds like what is going on with your tree.  There is no need to do anything to the tree except leave it alone.  

The flux occurs where there is some type of wound or crack in the tree.  Bacteria enter through the wound and are reproducing within the tree.  Since there is little oxygen in the tree, the bacteria undergo anaerobic respiration (fermentation).  The biproducts of this process are gas (hence the foam) and alcohol (yeasty odor).  

These bacteria are not really causing harm to the tree.  However, trying to treat the problem by drilling drain holes or filling the hole can cause problems.  Usually the flux is seasonal (spring and fall) although you may see staining throughout the year.  Often, the flux sites will naturally heal over several years and flux will no longer be visible.  

It is likely that you will see insects near the flux sites.  Flies, wasps and bees are highly attracted to the fruity odor.  To prevent the insects from visiting the sites, you can spray the flux area off with the hose.  It may be helpful to use a product such as a bleach solution (1 part household bleach, 9 parts water) to clean the area.  Again, this is only if the flux or insects bother you and it is not required.

Boring insects are not likely to be attracted to the flux.  If borers should attack the tree, it is usually because the tree is under environmental stress or stress from a plant pathogen.  To help alleviate stress, you should water 1-2 times a week during periods of drought.  It is important to water the tree deeply so that the water penetrates the root zone.  This means that you should leave the hose on a slow drip or light flow under the tree canopy for a while so that the water can be absorbed.  Watering the surface for a few minutes does not achieve deep watering.  You should also fertilize the tree as appropriate.  If you have not had a recent soil test, this would be advised to help guide you in the nutritional needs of the tree.  Lastly, avoid further problems by preventing mechanical injury (lawn mower rubbing is most common), proper pruning and removing dead branches.