Mistletoe is a parasite that weakens the tree a little but is not a major threat, although it is unsightly. There is not a good product labeled for use on mistletoe. If the mistletoe is on the outer limbs, you may want to prune it out. Cut the limb off two or three feet below the mistletoe whenever possible to make sure and get all of this pesky plant's parts growing within the limb. This however is often not practical and in a heavy infestation will leave you with almost no tree left!
I see it for sale during the Christmas holiday season so there is probably a market for it, although maybe not a big one. I think folks just pick it out of the tree and then sell it. Keep in mind that the small white berries are poisonous.
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