Mistletoe: There’s Nothing Romantic About It

Mistletoe may be good for those desiring a kiss but not so much for your trees…

We see a lot of mistletoe around here. Unfortunately, that doesn’t mean that love and lingering holiday cheer are in the air, but rather, that the seeds propagating the parasite are soon to be airborne. (And watch out: Mistletoe seeds are ejected from the plant at speeds of up to 60 mph!) It’s something to be aware of as mistletoe is detrimental to the health of your trees.

mistletoe
Note the abnormal branch growth of the witches broom on this fir. Photo by Cephas via Wikimedia Commons

North Idaho is home to a handful of dwarf mistletoes that are specific to our native trees. Larch, Douglas fir, ponderosa and lodgepole pines are all primary host species. In our work, we have seen it most often in larch and Douglas fir.

What does mistletoe look like? It’s most easily spotted when the infection is full-blown and affected limbs have witch-broomed in response. A witches broom is a mass of chaotic branch growth that appears as a dense clump in your otherwise well-formed conifer. The witches broom is a response to the mistletoe but not the mistletoe itself.

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Larch dwarf mistletoe shoots begin to sprout in the spring eventually forming clusters of shoots as seen in this plant. Photo courtesy of the USDA Forest Service Archive

Mistletoe is hard to detect early on. For several years, no outward symptoms may be apparent. This is known as a latent infection. After several years, though, scaly shoots emerge. However, since they are only two inches tall and are likely hidden in the canopy of the tree, most property owners don’t notice the early stages of mistletoe infection. Thus, we are often called in to treat more heavily infected trees that have had many years to spread the parasite to surrounding trees. This makes mistletoe eradication difficult.

Mistletoe harms trees in numerous ways. For one, as a parasite, it takes water and nutrients from the tree for its own growth, leaving the tree weaker and more susceptible to other insect and fungal invaders. Infected trees grow slowly, and heavy witch-broomed limbs are prone to breakage due to their weight. Mistletoe often leads to tree death. It also creates a fire hazard. All of this means that a mistletoe infested tree is a hazardous tree.

Our approach to mistletoe treatment is to first assess the tree to determine if the tree is a candidate for pruning or removal. If the infection isn’t too severe, pruning of witches brooms and less affected limbs will be undertaken. Healthy looking limbs adjacent to infected ones may also be removed in case infection is latent. Pruning in subsequent years may be necessary to catch future outbreaks. And pruning is best undertaken in the early spring or late fall when pollen and seeds are not being released from the mistletoe. We don’t want to inadvertently spread more infection.

One last thing to consider is that mistletoe does have its uses. Various birds and forest animals use witch-broomed limbs for cover and as nesting sites. We once found ourselves in a tree, dodging a group of flying squirrels leaping to safety. There is something to be said for leaving an infected tree alone if it is not a direct hazard to you and the health of your forest.

If you have concerns about mistletoe, give us a call for an assessment. And for more information, there are several helpful publications online: