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DALY: Despite folklore, mistletoe can be harmful to trees

Since most of the leaves have fallen off deciduous trees, mistletoe infestations are now visible. The plant is sometimes used in Christmas decorations. An old Christmas custom exists that when two people who meet under a hanging piece of mistletoe are obliged to kiss. It began centuries ago in Scandinavian countries. When two enemies met beneath the mistletoe in a forest, they would lay down their weapons. They would not attack each other until the following day. Despite its folklore, mistletoe is a parasitic plant that is detrimental to trees.

Mistletoe plants are either male or female. Only the females produce fruit. The berries are small, sticky and are white in color. They appear from October to January. Birds feed on the berries and excrete the seeds on to tree limbs. The birds can consume the berries without harm, but the fruit, as well as the rest of the plant, is highly toxic to people. After the mistletoe seed germinates, it develops a root-like structure that penetrates into the tree.

Trees in good health normally can tolerate small infestations of mistletoe. Individual branches with the parasitic plant may weaken and eventually die. However, trees that have suffered environmental stresses, such as drought and construction damage, or afflicted with another pest infestation, can decline and die as a result of the mistletoe.

The question arises: What should be done if a tree is infested with mistletoe? One of the important things to do is to remove the mistletoe before it produces berries and spreads to other parts of the tree or to other trees. The procedure of mechanically pruning out infected branches is one of the most effective ways of controlling it. Remove the infected branches back to where they begin on the tree or back to lateral branches. Cut at least one foot below the point of infection. If the mistletoe is growing out of the main trunk or a major limb and cannot be pruned, cut it back flush to the stem or trunk. Then wrap the area with a few layers of black polyethylene plastic to keep light out. Secure it with rope or twine. The mistletoe will eventually die. However, this may take several months.

Special chemicals are sometimes used to control mistletoe. They are highly toxic, and only licensed pesticide applicators can apply it. They are applied to dormant host trees causing the shoots and leaves of the mistletoe to fall off. The control is temporary. It will eventually re-sprout, and the chemicals will need to be re-applied one or more times before the mistletoe is destroyed.

For the removal of mistletoe from large trees, only trained professionals should attempt the task. Specialized equipment and expertise are required for the safe, effective control of this parasitic plant. You should consult with a certified arborist first to determine the exact extent of the infestation and its impact on the tree. A list of certified arborists and tree care companies can be found through the Georgia Arborist Association website at www.georgiaarborist.org.

Timothy Daly is an Agricultural and Natural Resource Extension Agent with Gwinnett County. He can be contacted at 678-377-4010 or tdaly@uga.edu.