Question
The leave of my oak tree are covered in a white cottony  fuzz. It falls off and some floats around When you put in between your fingers it is sticky like syrup/honey substance.  Is it harmful to the tree - if so, treatment??

Answer
Sounds like an insect called Cottony aphid. Aphids suck the plant juices and secrete a substance called Honey dew which is high in sugar content and sticky. Cottony aphids also produce a waxy material that is white and fluffy.

IF the tree is small and can be sprayed I would go ahead and spray the tree -foliage and branches with an insecticide called Orthene. IF the tree is large I would treat the soil around the tree with an insecticide called Bayer Advanced Tree and Shrub Insect control and the roots will carry the insecticide to the foliage and twigs killing the insects as they feed on the plant juices. This will protect the tree for the season.
Here is a web link to this product check with your local garden type store for it or the Orthene.

http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect