Using Mistletoe to Diagnose Tree Health

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The holiday season is upon us and gathering with loved ones is one of the ways to celebrate. The age-old tradition of hanging a bundle of mistletoe in a doorway to inspire unsuspecting couples or individuals to kiss is still practiced to this day. What you may not realize is that the mistletoe plants around the world are hemiparasites, meaning they “root” into a host plant for water, nutrients, and support, but have the ability to also make their own sugars through photosynthesis. This means when you see a mistletoe plant on a tree, you are observing a weakened, unhealthy tree.

North American Mistletoe

European settlers brought the kissing practice with them, where they used the mistletoes native to Europe in the tradition. North America’s mistletoe is a good surrogate though. The “leaves”, berries and overall form are very reminiscent of the European mistletoes. The species is Phoradendron leucarpum, and is in the same family, Santalaceae, as those in Europe. The second part of the scientific name refers to the white (“leuco”) berries (“carpum”) that the mistletoe has.

The family Santalaceae is full of parasitic plants that have developed the survival strategy of latching on to nearby plants for water and sugars. It may seem “harsh” or “selfish” of these plants, but remember not to ascribe human emotions to plants. They are just getting by!

What’s the Problem

If mistletoe is such a beloved Christmas season tradition, what is the issue?

Birds love to eat the white berries, and it is through birds traveling and leaving their droppings behind that mistletoes spread from canopy to canopy. The berries have a sticky layer around them that helps them stick to the bark of potential host trees. The issue comes when trees are weak and are not able to stop the seed from burrowing its haustoria, similar to roots, into its branch. Usually trees have chemical defenses that stop this from being successful, but if a tree is not healthy, it will not have the energy to create these chemicals.

Mistletoe is a native plant, despite its survival strategy, and it is just taking advantage of a situation. It can become an issue when there are too many mistletoe plants growing on a tree for that tree to support its own growth. It isn’t uncommon to think that your tree is “evergreen” because of how many mistletoe are growing in it. This isn’t good for the health of the host tree though.

What Can You Do?

The dormant season is an excellent time to observe mistletoe in deciduous trees, or trees that drop their leaves in the winter. You can see the globe-like mistletoes seemingly floating in the canopy. Seeing one of two is okay, but if you see more than 50 percent of the canopy full of mistletoe you know you have an unhealthy tree.

There are a few things you can do to help trees live healthy lives. A first step is to remove grass in the immediate root zone and replace it with some kind of organic matter or mulch. This reduces the root competition between the trees and the grass, and reduces the likelihood of you scalping the roots as you mow. The next thing is to reduce walking and driving around the roots of the trees, if you can help it.

Mistletoe is Not Bad

Mistletoe plants are part of the ecosystem and serve as indicators of plant health. Keep an eye out for these plants in your trees and consider giving some extra attention to those trees in your landscape management plan.

Amanda Wilkins is the horticulture agent for North Carolina Cooperative Extension in Lee County.