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Gardening in Gwinnett: Mistletoe can be potentially harmful to trees

Since the most of the leaves have fallen off of the deciduous trees for winter, growths of the mistletoe plant are quite visible in trees, such as oak, Bradford pear, birch, walnut and zelkova, amongst others, throughout the area.

Mistletoe is commonly used in Christmas decorations. An old Christmas custom is that any two people who meet under a hanging piece of mistletoe are obliged to kiss.

Despite its folklore, mistletoe is a parasitic plant that is detrimental to the health of the trees it infests. Mistletoes are either male or female; only the females produce fruit. The berries are small, sticky, white in color and 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 known as haustoria that grows into the tree's vascular system and feeds on the water and nutrients. The parasite prefers smaller branches 1/2 to 3/4 inches in diameter.

The plant has succulent stems with oval-shaped leaves. In time the plants can grow up to several feet in diameter. 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 been weakened by environmental stresses, such as drought or construction activity, or suffering from another pest problem as well as any tree that has a heavy infestation of mistletoe will eventually loose vigor, decline and could potentially die.

The question arises: what should be done if a tree is infested with mistletoe? There are several control methods, which should be done by trained professionals in most cases. One of the important things to do is to remove the mistletoe before it produces berries and spreads to other parts of the trees or to other trees. The procedure of mechanically pruning out infected branches is one of the most effective ways of control.

The earlier the pruning is done, the better to remove the mistletoe before it becomes 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 to completely remove the embedded haustoria. If the mistletoe is growing out of the main trunk or a major limb and can not 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 and then secure it with rope or twine. The mistletoe will eventually die, but this may take a few months or even years.

Another method of control is the use of the chemical plant growth regulator Ethephon, sold under the trade name Florel. The chemical is applied to dormant host trees causing the shoots and leaves to eventually fall off. The control is temporary because it will eventually resprout and eventually the chemical will need to be reapplied at least once, maybe more, before the mistletoe is completely destroyed.

The chemical Florel is highly toxic and acidic, and only licensed professional can apply it. 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 Web site at: www.georgiaarborist.org or you can contact the Extension office.