I live in Multnomah County, in a Portland Neighborhood. 

I planted 2 columnar apple trees in 2015 a Golden Scent (dwarf) and a North Pole (Red). Both trees have done well until this year.  The Golden Scent has turned yellow and brown and I don't know why.  The North Pole is fine.  This is the first year I have fertilized my apples (I have 2 espaliered apples as well).  I used Dr Earth (5-5-2) Natural Wonder Organic & Natural Fruit Tree Fertillizer and followed the directions. 

Any clue as to why this has happened?  All 3 other trees are looking great.  I have photos that I will include.