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DALY: Mistletoe can kill trees that have suffered environmental stresses

Since most of the leaves have fallen off deciduous trees, mistletoe infestations are now visible.

The plant is commonly used in Christmas decorations. There is an old Christmas custom that any 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 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 the health of the trees it infests.

Mistletoe plants are either male or female. Only the female ones 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 of it on 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 itself.

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. The sooner it is removed, the better the chances are of preventing it from becoming a major problem.

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 out, 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.

A chemical called Florel is sometimes used to control mistletoe. It is highly toxic and only licensed pesticide applicators can apply it. The chemical is 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 chemical will need to be reapplied one or more times before the mistletoe is completely destroyed.

For the removal of mistletoe from large trees, only trained professionals should attempt the task. Specialized equipment and expertise is 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.