Kelly Jackson
Christian County Extension Office
Mistletoe
Once autumn leaves have fallen, mistletoe becomes highly visible on large trees throughout Kentucky. Phoradendron, the scientific name for this parasitic plant, means tree thief. You can commonly find these small leafy plants on twigs and branches of many hardwood species in the southern two-thirds of the United States. Mistletoes extract water, mineral elements and food from their host tree by way of a parasite nutrient-uptake organ; hence the name, tree thief.
Mistletoes’ use in holiday traditions has roots in pagan times. Its parasitic nature and the fact that it appears to be alive while the host tree appears dead, led some to believe mistletoe mysteriously held the life of the tree during winter. Druids harvested mistletoe in a special rite, never letting the plant touch the ground, then hung it in their homes for good luck.
Our modern-day mistletoe holiday tradition likely originates with a mythological Norse goddess of love and beauty. Frigga, whose son was restored from possible death by mistletoe, was thought to bestow a kiss on anyone walking beneath one. Today, when two people meet under the mistletoe, tradition suggests they must exchange a kiss for good luck.
Phoradendron, the most common mistletoe growing in Kentucky, resembles another species that grows in Europe. It has simple, fleshy green leaves arranged oppositely on the stem. Stems are short and more branched than the host tree, so mistletoe often appears as a spherical bunch of dense vegetation. These bunches may be a foot or two in diameter and are located high in the tree for better sunlight exposure. Mistletoe berries range from white to straw-colored to light red. Birds eat the fruits, reportedly toxic to human and animals, then deposit the seeds onto branches where they germinate and penetrate the host tree.
Since birds tend to roost in open-grown trees, mistletoes do not appear as frequently in forest trees. Generally, they do not cause much damage, although they can be harmful to a tree already under stress.
If mistletoe appears on landscape trees or other trees in the urban forest, the most effective control method is to prune out infected branches as soon as the early infestations become apparent. Infected branches should be removed at their point of origin, or back to large lateral branches. Infected branches need to be cut at least one foot below the point of mistletoe attachment in order to completely remove the embedded roots.
Occasionally, severe pruning may be required to remove heavy mistletoe infestations. However, such pruning may often weaken a tree’s structure and destroys it natural form. In some cases, it may be best to remove severely infested trees, since they are usually a source of seed for mistletoe spread to nearby trees.
Mistletoe infecting a major branch or the trunk where it cannot be pruned may be controlled by cutting off the mistletoe flush with the limb or trunk. The area should then be wrapped with several layers of wide, black polyethylene to exclude light. Use cotton twine or flexible tape to secure the plastic to the limb. Since mistletoe requires light, it will die within a couple of years. It may be necessary to repeat this treatment, especially if the wrapping becomes detached or the mistletoe is not completely killed.
Simply cutting the mistletoe out of an infested tree each winter, even if the wrapping procedure isn’t carried out, will help. Even though the parasite will grown back, spread is reduced because mistletoe must be several years old before it can bloom and produce seeds.
Research conducted in other states indicates that growth regulators, such as ethephon (sold under the trade name Florel), are effective in controlling mistletoe. To be effective, the spray must be applied in the dormant season and thoroughly wet the mistletoe foliage. In some cases, a single application of ethephon effectively controlled the mistletoe, whereas multiple applications of the growth regulator were required for heavily infested trees.