Yellow Leaves on Pin Oaks

Chlorotic Oak Tree

If you have a pin oak with pale green or yellow leaves, it is most likely suffering from a condition called Iron Chlorosis. Basically, this is an iron deficiency caused from a lack of usable iron in the soil. Iron Chlorosis causes the leaves of affected trees to turn yellow and prematurely drop from the tree. If left untreated, over time the condition can lead to branch die back, and, eventually, death of the tree. The condition is treatable, however.

The Utah State University Extension Office has a handy treatment table here: http://extension.usu.edu/forestry/HomeTown/care_irontable1a.htm