Question
Hi, can you help me. I live in Melbourne Australia and my mature oak has just in the last 2 months developed a black tar weeping from the middle of the trunk.  It seems to be getting worse and I want to save the tree as it is a beautiful mature oak.  I suspect some sort of fungi but don't know much about these or how to treat it.

Answer
Maree:
I suspect that this seepage may be due to an injury or opening in the bark. The opening may have been caused by an insect (borer) or perhaps a microorganism that entered through an opening/wound. If it is an insect or disease organism, maintaining good fertilization and adequate water is the best.  Trees, if care for in these areas can withstand a lot of "attacks" and still persist for many years.  There is an insecticide (if the cause is indeed an insect) that can be applied to the soil and is taken up into the tree.  The product is called Bayer Advanced Tree and Shrub Insect Control.  It is a liquid that needs to be diluted first.

If you wish, you can take and send me a closeup photo of this area.  I have an entomologist next door to me and I can show them to maybe give you an idea.  If possible, hold a ruler or some common small object next to the opening so I can have an idea of the size/shape.  Be sure to review your photo on your computer to be sure it is in focus before sending.  In the meantime, using your computer, look at "borer damage on trees" in "Google Images" for a photo that may match your tree.

Regards
Steve