Any idea what would cause a tree limb to grow like this?

[woodman]

I have watched this tree over the last few years and wonder what the heck the reason why this limb would grow like this. It is a tight ball of growth that just gets bigger each year. It now is about two or three times the size of a basketball now. Whenever I get near it, it catches my attention and it is just a head scratcher to me.

[KFhunter]

atrazine


just kidding,  I don't know 

cool though

[MtnMuley]

Mistletoe

[KFhunter]

Mistletoe

bingo!


http://www.na.fs.fed.us/spfo/pubs/fidls/d_fir/dmistletoe.htm

[woodman]

I am always amazed at the sheer mountain of knowledge on this site. You guys are genius. Thank you so much for taking the time to give the answer that I really did not think that I would get

[MtnMuley]

Although it looks cool, it's very detrimental to the health of firs. The spores will burst, spreading the disease to the whole stand of trees.

[KFhunter]

I learned about it in FFA and AG science years ago - I'd forgotten 


but now that mtnmuley fingered it...if it's your stand of trees I'd cut it out. 

[ghosthunter]

http://ext.nrs.wsu.edu/forestryext/foresthealth/notes/dwarfmistletoe.htm

[runamuk]

Witches broom
http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/witches-broom.aspx

highly coveted when it is a mutation that can be reproduced ..... not always caused by disease.....they are very cool and if you wanna harvest it you might find a buyer...google a little.... might be worth a buck or two