Question
I live in Northern California, the San Francisco Bay Area.  I have lived in this house for 25 yrs.  One of my large oak trees has started dripping a very sticky sap.  It also did this last year.  I can see that 2 large limbs are dead and need to be pruned.  I can see some length wise splits in the bark.  What is the average life of an oak?  I would hate to lose this tree.  Can you tell me why it is dripping the sap?  

Thank you very much.

Answer
Sounds like either an insect called an aphid or a scale insect. Both suck the plant juice from the foliage and twigs and secrete a substance called honeydew which is high in sugar content and sticky. Control the sucking insects and the sap will stop dripping. Apply an insecticide to the soil around the tree. Treat with  an insecticide called Bayer Advanced Tree and Shrub Insect control. The roots will absorb the insecticide and transport it to the foliage and when the insect suck the plant juice they are killed. Check with your local nursery for this insecticide. Here is a web link to more information on this product.  http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html

Oaks are long lived 100+ years. I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb of fertilizer per inch of trunk diameter scattered around the tree and watered in good. Do this now and again in the spring. Fertilize just before a rain storm and you will not have to water.