Mistletoe: Is the Christmas plant friend or foe?

Mistletoe may be a welcome holiday sight when hung over a doorway if a loved one is near, but, it can be an unwelcome intruder when found in your trees, said a Texas A&M AgriLife Extension Service horticulturist.

“Mistletoe is a hemiparasite – a semi-parasitic plant,” said Allison Watkins Schwarz, AgriLife Extension horticulturist for Tom Green County. “It makes its food from photosynthesis, but the roots grow into the host tree, sucking water and minerals out from the sap.”

In other words, you likely do not want to see mistletoe growing on your favorite shade tree or prized ornamental. Because once it inhabits the tree, it can survive as long as the tree lives, meaning some mistletoe alive today may still be around in 100 years.

The plant has been used across various cultures throughout history for everything from warding off demons from entering a doorway to protecting babies from fairies stealing them from their cribs in the night.

And although it is called the kissing plant, its name may have originated from Old English for the words for twig and dung. How’s that to get you in the romantic holiday spirit?

The issues with mistletoe

One type of mistletoe commonly used as decoration over the holidays is in the family Phoradendron, which appropriately translates to “thief of the tree” in Greek.

Schwarz explained that mistletoe causes tree stress and can make a tree more susceptible to diseases and insects. Although unlikely to kill a healthy tree, it can cause limbs to die and can be especially hard on trees during drought.

As birds eat the mistletoe berries, they spread the seed from limb to limb and tree to tree through their feces. The seeds are exceptionally sticky and may also hitchhike on birds’ feet and beaks.

Certain species of mistletoe can also shoot out their own seeds at speeds around 60 mph once the berry bursts like an overfilled water balloon.

Although birds and wildlife eat the berries, they aren’t something you want your family members, including pets, to ingest, because some mistletoe is poisonous. So, it is always wise to use care when handling the plant. Different parts of the plant and different species have varying levels of toxicity.

Identifying mistletoe in nature

Mistletoe is most easily spotted in winter when many of the host trees lose their leaves to reveal clusters of the evergreen mass. The spherical shape can be as large as several feet across.

Since birds like to perch in the tops of high trees, mistletoe is most often found in mature trees near the crown. A tree branch may be enlarged where the plant has attached itself.

In Texas, the type found on trees typically has white berries in clusters. Although mistletoe in this region is typically found on deciduous trees such as oak and mesquite, the plant’s 1,000-plus species around the world have adapted to survive on everything from cacti to pines.

A friend to forests, pollinators and woodland creatures

Mistletoe plays a positive role in many woodland and range ecosystems. For example, its white flowers provide nectar and pollen for native bees and honeybees. There are also several types of butterflies and moths that rely solely on mistletoe species as host plants for their caterpillars.

Birds and squirrels will eat the berries, and deer and porcupines will eat the plant itself, especially during times of food scarcity.

Many animals nest in clumps of mistletoe, especially when the plant causes its host tree to form witches’ brooms, which are dense masses of distorted branches. Mistletoe and the corresponding witches’ brooms are used for shelter by tree squirrels, flying squirrels and a variety of birds, from tiny chickadees to raptors like Cooper’s hawks.

The damage done to trees by mistletoe can also provide homes for cavity-nesting species of birds, bats, insects and small mammals.

Should you remove the plant?

“Even if you remove mistletoe from a tree, the root-like structure remains embedded in the tree, meaning it will grow back,” Schwarz said.

No herbicide can kill mistletoe without harming the tree, but one plant growth regulator called ethephon, Florel Fruit Eliminator, is registered in the U.S. to control the growth of mistletoe on deciduous trees, she said.

The only way to eliminate mistletoe from a tree is to prune the branch it is on. Keep in mind that it takes two to three years to mature, so the sooner you can remove the infected branch the better you can control the spread. And the smaller the branch that must be removed, the less stress on the tree.

“In most well-maintained landscapes, there may be mistletoe here or there but it’s probably not something to worry about too much,” Schwarz said.

The stress from over-pruning could be more damaging than the mistletoe itself, she said, and offered these tips if you do decide to prune:

• Light pruning can be done any time of the year, but more significant pruning is best done in the winter when the tree is dormant.
• Prune no more than one-third of a tree’s canopy.
• Dead branches can be removed at any time.
• To avoid spreading oak wilt, oak trees should not be pruned from February to June. December and January are the ideal time to prune oaks, just make sure the cut wood is not transported to other areas as oak wilt disease and unwanted pests can then spread.
• Paint the areas where the tree has been cut to protect the tree.

For more information, visit Forest Health: Mistletoe by Texas A&M Forest Service.