Question
I planted 3 blue spruce a couple years ago. The eastern-most tree is rusted from top to center, and I assume it is actually dead. What would cause this?

Answer
It sounds like only one tree is impacted, and that the impact is in upper half only.

This therefore isolates the impact, making soil or moisture related issues somewhat less likely.

I would suggest that it is likely caused by an insect, possibly the white pine weevil.  

The white pine weevil will attack various species pines and spruce trees.  Symptoms of the white pine weevil are typically a dead or dying central leader.   There will often be a wilted, droopy and curled central leader.

There are also other possible insects, some bark beetles which kill the top.  For them you may see spruce pitch oozing from the bark at the base of the red needles.  

Depending upon how much of the leader is dead, will determine if the tree can be saved.  

If the top is dead, you will not be able to save the dead portion. You can verify if it is dead by taking a small branch/twig which appears dead and see if the wood is dry and brittle or if it is soft and flexible (this will depend upon how long it has been dead).

If it is dead you will need to remove and destroy the dead portion.  

Depending upon how much of the tree this is, will determine if you can save the tree (would have to be 20-25% dead maximum).  

If a fairly small portion is dead (less than 20-25%), cut off the dead portion and one of the side branches will become dominant and form a new central leader.  That is if you are willing to wait as it will take several years and look somewhat unsightly at the beginning.

If when you check the limb for health, it appears soft, flexible and still not dry, then you can try treating with Onyx or Merit.  This treatment should kill the insects, and the tree may recover.  You will however need to keep a close eye on the tree, and if it continues to die then you may still need to remove at minimum the dead portion.  

If you do find the wood to be dead, dry and brittle, then at minimum the deadwood must be removed and destroyed.  If it is a significant portion of the tree, more than 20-25% then the whole tree may have to go.

If you have pictures please send.

Thanks.