Question
We have a Red Oak that drops a large amount of sap and leaves a mess on the driveway, vehicles and anything else left under the tree.
There is a Chinese Pistachio on the other side
of our driveway, could this have anything to do with it?  We live in the Zone 8b area.
The sap problem is really bad, and my husband is considering cutting the tree down.  It is about 13 years old, so we don't really want to lose it since it provides great shade.  

Thank you for any information you might be able to provide.

Answer
Sounds like the problem is not with the tree but the tree is infested with an insect called aphids. These soft bodied insects suck the juice out of the leaves of trees (plants) and secrete a substance called honeydew--that is a sugar based liquid that is sticky. Normally a fungus grows on this honeydew called sooty mold--making the leaves appear to turn black. I would suggest you spray the foliage of the tree with an insecticide for aphids--this will stop the "sap" dripping on everything. Check with your local nursery or garden type store and ask for an inseccticde for aphids that can be sprayed on trees. I would ask for a "systemic" type insecticide since it will work better then a regular contact insecticide. Control the aphids and your sap problems will go away.