Oak Tree ailment?

  Hi, I found the following Q+A online, which may help you. Q: Sticky sap is dropping from our oak tree and it is turning the deck black. It can be washed off but within days it is covered again. Is this something I can prevent? A: Your oak tree isn't shedding sap, you have an aphid problem. The black stuff on your deck is called "sooty mold" which is the waste that the aphids release after sucking the juices from your oak trees leaves. In other words this sap is the "poop" of the aphid. After a while the sticky excrement develops a black mold and this is what you are seeing on your deck. The only way to keep this from happening is to keep washing off the deck on a weekly basis or treat the oak tree for aphids, if it isn't too big for you to do yourself. Any approved insecticide for the control of aphids will work. Liquid "Sevin" is ideal for this. I can almost bet that you also have an ant problem on your tree also. The ants feed on this excrement that the aphids release. Get rid of the aphids and your sooty mold problem will be gone too. Hope this answers your question.   Best wishes!

the only thing (living thing) we have an abundance of this year is snails.  Tiny ones, medium size ones, large ones, white stripey and brown.  They are everywhere, climbing in trees, shrubs, garden gate posts even the glass doors, house fascia and terraces.  Even in England I have never seen so many snails!!  Not sure what snail poo look likes:-) but don't think they have infiltrated the old oak. Thanks for the response though fellini

Sounds like the droppings of some sort of caterpillar to me and there's not a lot you can do about a mature tree, however take heart because the oak serves as a refuge for a huge number of critters without a lot of damage being done. The tannins will go in one end of the pest and out of the other and the blue stains are as a result of a reaction with iron in the stone

given this stuff was dropping like rain that would need to be an awful lot of caterpillars!  Haven't seen any but then the tree is very large and as growing on a slope the base alone is 10 feet above eye level (apart from when we venture up the slope, obviously).  The tree has a  large dead limb so maybe something to do with that?  Dead wood attracting something?  We have now got permission to remove the dead limb but given its position on a slope but overhanging garden and close to house, finding someone qualified and with the right equipment to deal with it is proving difficult.  At least it sounds as though the plants dying are not as a result of whatever is dropping from tree.  Maybe young Harry is cocking his leg a little higher than we thought :-)

http://www.treehelp.com/trees/oak/species-oak-iandd.asp