Xmas Countdown Xmas Stories

The magic of mistletoe

Tis' the season to be jolly, and to be on the lookout for pests that can affect the overall health of your trees! Mistletoe is one of the classic Xmas decorations shrouded with tradition and myth, from the health of trees to the obligatory kiss beneath and those "poisonous" berries. Maybe with a bit of Xmas cheer, we can debunk and clarify mistletoe facts from fiction. Although it is unclear where the myths of mistletoe begin exactly, its lore is said to originate with ancient druid tribes in pre-christian Europe where European mistletoe, Viscum album, if taken from oak trees, had special powers, including boosting male fertility and ending barrenness in animals. In a Norse belief, it was an arrow made of mistletoe that was able to kill Baldr, the Norse god of light, and the lesser known brother of Thor. Although one would believe, with such a mythical heritage, that the word mistletoe would have great meaning, it loosely translates from Greek, meaning "a twig with droppings," most likely stemming from the fact that the plant is spread primarily by birds. Think about that the next time you are waiting for a kiss from your special someone!

American mistletoe, Phoradendron serotinum, is considered a parasitic plant that can thrive in dozens of species of trees. The plant is considered parasitic due to its unique ability to "trick" a host tree into feeding it nutrients and water. Mistletoe is spread in many different ways, including gravity and wind, but primarily by birds that eat the fruit. Many things must happen for mistletoe to be able to grow in the canopy of a tree. The tree branch that the berry lands upon must be the correct diameter, fast growing and have thin bark. For this reason, along with the lack of sunlight, infection of very old branches in the canopy of trees is rare. Infection more often takes place in the outer-edges of the tree canopy on new limbs. Generally, the tallest trees, or those that are standing alone, are more likely to become infected. Although mistletoe is present all year, it is usually only noticed in the fall and winter, after the leaves begin to fall.
Mistletoe has the innate ability to commandeer water and nutrients from the host tree. If given the chance, the first thing that the plant does is insert root-like structures, called haustorium, into and under, anchoring the plant to the tree. These haustoria work their way beneath the bark, and into the vascular tissue of the host tree. Here, they steal nutrients (the Latin translation of Phoradendron literally means "tree thief") from the tree and continue to grow. Generally a tree is capable of protecting itself from wounds and other invasive damage by a process called compartmentalization, which seals the area from receiving water and nutrients. Mistletoe however, "tricks" the tree into not recognizing that it is a pest by secreting hormones and enzymes to prevent the tree from undergoing compartmentalization, thus continuing its supply of water. Once established, and therefore visible from the ground, mistletoe is capable of manufacturing its own food through photosynthesis though it continues to steal water from the tree, often in very large quantities. In times of drought, trees that are infected with large amounts of mistletoe can die due to this theft of water. Mistletoe can also cause girdling of branches, causing them to die and eventually fall off. This can also lead to structural damage within the tree, causing branch failure.
Although mistletoe is considered a mild hazard to a host tree, it also is a beneficial organism that supports a vast array of wildlife, primarily birds. Many of our common favorites rely on mistletoe: mockingbirds, bluebirds, yellow-bellied sapsuckers, both red-bellied and pileated woodpeckers, and cedar wax-wings, just to name a few. These birds eat the berries from the plant and then deposit them elsewhere in their waste. This source of food for birds is especially important during times of drought. While birds can eat the berries, it is not recommended for humans or pets to consume any part of the plant. In a study by the poison control center over four years, 92 people across the US were reported to have ingested bits of the plants, including berries and leaves. Of these 92, only 12% reported any symptoms from the plant, most commonly gastrointestinal distress. Many of the myths and rumors of the toxicity of the plant most likely stem from the concentration of different chemicals in the plants when used as a tea or medication. While not so poisonous, the plant does contain calcium oxalate crystals, a major component of human kidney stones. These crystals, known as raphides, act as mechanical defense to ward off animals, and humans, causing pain in the mouth and throat of the consumer.
Controlling mistletoe is most simply accomplished by removing the green part of the plant or to correctly prune off the infected branch. Although this does not actually kill the plant, it hedges off the water stealing capabilities for a while. The only problem with this is that the plants are often located many feet off of the ground, so it may prove impossible for the homeowner to accomplish this. Remember, mistletoe alone will not cause the tree to die; it can only be one of many contributing factors. Whether or not Burl Ives' famous line "Ho ho the mistletoe, hung where you can see. Somebody waits for you, kiss her once for me..." will actually work, well that's still up in the air.