Magnolia Tree problem

My magnolia tree (about 30 years old) appears to be diseased. The branches are covered with this solf white cotton-like substance and it keeps continually dripping this sticky sap. What is this and what can I do about it?

 

Sounds as if it may be Magnolia scale.

http://images.google.com/images?q=m...1I7SUNA_en-GB&um=1&ie=UTF-8&sa=N&hl=en&tab=wi



http://www.ca.uky.edu/entomology/entfacts/ef431.asp

 

Thanks Silver Surfer for a prompt reply. I googled further of Magnolia Scale and that's exactly what it is. Now to the task of trying to rid of it. Sounds challenging.