What is the black smooge on our tree?
Your tree is suffering from a condition known as 'slime flux'. The causal factor is typically a wound of some sort that could be the result of insect activity, mechanical damage, or simply a split in the bark resulting from temperature or moisture fluctuations. The wound will allow a bacteria of some kind to get into the vascular system of the tree. The infection will then cause the sap to ferment and bubble out of the wound. The fermented sap will frequently attract lots of insects and in your case, apparently encouraged the formation of a mold known as 'sooty mold'. The mold does not hurt the tree and it appears from your photo that the tree has already isolated the wound and stopped the flow.