Despite the fact that mistletoe remains a popular Christmas decoration with its bright green leaves and white berries, it is a parasite of trees. As a result, mistletoe can harm trees.
Mistletoe also has poisonous properties and should be kept out of the reach of children who may be tempted to eat the berries.
Mistletoe can harm trees in several ways. It gets water, essential elements and some food from its host tree. Chemical signals from mistletoe confuse tree growth and transport systems. Local food supplies are continually used by the parasite. Eventually as more clumps of mistletoe grow, the tree begins to decline. Old, slow growing trees are most susceptible to attack. Mistletoe seldom infests young, vigorous trees.
Every clump of mistletoe is male or female, not both. Only female clumps produce the white to pink colored fruit, which has been traditionally used for hanging to perhaps kiss the suspecting or unsuspecting person who stood beneath it.
Mistletoe is spread mainly by birds. Birds eat the fruit and then seeds pass through the birds and stick to branches. Falling fruit from clumps of mistletoe can stick to limbs below. Once a seed is stuck or lodged on the branch, growth of a new plant can begin.
The seed germinates and grows a root-like stub that pushes against the branch. This modified root works its way into bark openings to the cambium layer. Soon the root of the parasite is well connected to food supplies. Several growing seasons may pass between seed germination and leaf development. During this time the root stub continues to grow and is fed by the tree.
Mistletoe is difficult and in many cases impractical to control due partly to the way it’s connected to the tree. And, mistletoe growing high up in the tree is difficult to reach.
Just breaking away the mistletoe is ineffective because it may redevelop at the point of removal. Systemic herbicides can move through the mistletoe into the tree, injuring the tree. You may have heard of a chemical growth regulator (ethephon) used as a method to control mistletoe but its practicality is questionable.
The most successful method of eliminating this parasite from a tree is through proper branch removal. The entire limb should be pruned at least one foot below the point where the mistletoe is attached.
Once mistletoe has been removed, there is always the chance that additional mistletoe will again find its way to your tree via birds.
More information is available at the following UF/IFAS website. http://solutionsforyourlife.ufl.edu/hot_topics/lawn_and_garden/mistletoe.shtml