Our young orange tree (planted in the spring) has been healthy but growing slowly. I’ve noticed light blue spots on the leaves, as if it had been sprinkled with kool-aid and it evaporated, but otherwise it seemed to be doing well so I ignored it. 

We recently fertilized all of our fruit trees with citrus tree fertilizer, and they all perked up except for the orange tree. Its leaves are starting to yellow. 

Any ideas on what is going on or how I can help it?  I live on the east coast of Florida.