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Mistletoe: Friend or Foe

posted Nov 16, 2010, 10:37 AM by Bob Whitney   [ updated Nov 16, 2010, 10:45 AM ]
Talking about mistletoe (Pharadendron sp.) this time of year usually reminds you of the Christmas season, presents, stealing a kiss, etc. but unfortunately that is all the pleasurable thoughts most have of mistletoe because it is a parasite for trees all the rest of the year.

A parasite is an organism that derives its survival from another living entity in this case mistletoe is the parasite and trees are the living entity on which it must survive.  In this area we see most of the mistletoe on American elm, cedar elm, hackberry and blackjack oak.  For some reason these trees seem to be easy hosts for mistletoe to grow in.  Mistletoe is dependent on the host tree for all water and dissolved minerals.  It is however, a chlorophyll containing plant which manufactures the sugars and starches needed in its growth and development.  

Mistletoe stems bear conspicuous green, leathery leaves which persist for several seasons.  Nutrients and water are supplied from an absorbing system called haustoria which develops in the bark and wood of the host tree.  Flowers are born in the leaf axil and produce the familiar, nearly clear, whitish berries in late fall and winter.  These berries are very poisonous to humans so don’t let children play with mistletoe.

Within the tough outer coat of the berry is a single seed which is embedded in a sticky pulp.  Birds feed on this sticky pulp and discard the seeds which stick to their bills, feet or other parts of the body.  In this way the seeds are carried to other trees or other branches of the same tree and deposited on the bark.  When conditions are right the seeds germinate sending root-like structures into the host plant and another parasite is developed.

There are no sure fire ways to control mistletoe.  (Click for a difficult but possible partial control) You can break it off but it will eventually grow back.  It is recommended that you cut a limb at least 12 inches down the limb from the mistletoe to insure that you get all the roots.  This of course could really make your tree look bare if you take all the mistletoe out.  There are no chemical controls that are currently effective.  Weed or brush killers are not recommended because they can move the chemical into the tree through the mistletoe. Mistletoe seldom kills a tree but it can weaken a tree so that it becomes infected with other tree diseases.  Having said this, the potential that mistletoe will severely harm a tree is minimal.
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