What causes spruce branches to drop their needles?

Question

I have a spruce tree that has a problem. Every year, some branches suddenly drop all of their green needles and die. I would like to prevent this, but I don't know what the cause is. What causes this and how do I prevent it?

Are there symptoms before the needles drop off? Can you please post a photo or two of the tree, showing an infected area before and after needle drop... — Mike Perry, Oct 18 '11 at 02:53
I could take a before picture, but I cut off the after. I haven't noticed any symptoms. — J. Musser, Oct 20 '11 at 01:15
Have a read of this: Needle Drop on Spruce & browse the results of this web search (1st page contains a lot of useful information): Spruce Dropping Needles — Mike Perry, Oct 20 '11 at 15:48
What time of year do they drop? And is it just light-green new growth that drops needles, or whole branches back to the trunk, or... — Ed Staub, Dec 02 '11 at 00:11
@Ed Staub Normally they die during the period after the new growth ripens and before it cools down at the end of the year. The whole branch just dies right up to the trunk. — J. Musser, Dec 04 '11 at 02:38

score 4 · Accepted Answer · edited May 23 '13 at 14:06

RUST vesicular OF NEEDLES (Chrisomyxa spp.)

fungal parasite

Symptoms: Yellowing of needles younger during the summer, for a portion or in their entirety. Subsequently emerge from the needles attached vesicles elongated, finger-like white or orange to rust, which would break with ease emitting abundant spores. Following the loss of the needles.

PREVENTION: If the vesicles are white, the spores can infect rhododendrons, resulting in the appearance of typical rust, and then ritoornare to infect the fir. Provide deleting or moving the rhododendrons from the immediate vicinity of the plants fir attacked.

CARE: Remove infected branches, dealing with specific products only in case of massive infestation.

What causes spruce branches to drop their needles?

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