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Dwarf mistletoe: Fun to kiss under, but deadly to northern MN Trees

Drawing courtesy: Washington Post
A sprig of Mistletoe has been fraught with meaning for thousands of years, becoming wildly popular during Victorian times. As author Washington Irving wrote about the plant in 1820: “the mistletoe, with its white berries, hung up, to the imminent peril of all the pretty housemaids.”

Mistletoe, a symbol of fertility, life, friendship and love, typically dangles from doorways during Christmas time, inspiring plenty of smooching! 

The dark side of Mistletoe

But as Utah State University Forest Pathologist and Professor Fred Baker points out, at least in our state, Eastern spruce dwarf mistletoe plays a much more sinister role. It is actually a disease that kills trees quickly, with most trees dying within 20 years.
Stand of black spruce trees infested with dwarf mistletoe.
The plant creates "witches brooms" in the branches.
Photo: Brian Anderson

Deadly to northern Minnesota trees...

Many stands of black spruce in northern Minnesota suffer from this fungal pathogen

The dwarf mistletoe disrupts a tree’s physiology in many ways. The most common sign is the formation of a witches’ broom, a clump of small, weak branches arising from one point on a larger branch. 

In this process, the disease diverts the tree’s nutrients to the broom and “starves” the rest of the tree. Ultimately, the tree will die because it’s unable to process the lipids it needs to survive. 

Mistletoe is called a hemi-parasite, "hemi" meaning the plant gets some of its energy from the sun (photosynthesis) and the rest--water and nutrients--is extracted from the tree. 
The reddish sprigs are mistletoe sprouting from the branch.

Yes, it actually shoots its seeds in the air!

Mistletoe spreads by seed. 

In an article he wrote for MyMinnesota Woods, Professor Baker explains just how this dwarf variety spreads: 

"When seeds disperse, dwarf mistletoes are unique because they can shoot their seeds up to 55 feet from a diseased tree! These seeds are covered with a sticky substance that attaches to a nearby spruce needle.  During summer rainfall, this sticky substance rehydrates, and the seeds slide closer to the twig, where it germinates the following spring." 

When mistletoe seed lands on a suitable host, it sends out roots that penetrate the tree.

Baker continues: "Although dwarf mistletoe can shoot seeds up to 55 feet, most only go a few feet. This results in a spread rate of about 2.4 feet per year through a forest stand. Research indicates that spread from large trees and small trees is about the same. Slightly more than half the spruce stands in Minnesota are thought to be infected with dwarf mistletoe." 

How to get rid of dwarf mistletoe

Getting rid of this mistletoe parasite is challenging since not all infected trees show outward signs like growths of vegetation (witches' brooms). 

Baker suggests that removing all spruce trees during a timber harvest could minimize the risks of mistletoe infecting a future stand. Because if you kill the tree, the mistletoe dies, too.

Where did the name 'mistletoe' come from?

There are more than 1,000 varieties of mistletoe throughout the world. They don't all shoot their seeds up into the air--in the case of many of these plants, the whitish semi-translucent berries fall and stick to whatever they land on. Since birds love the berries, they excrete the seeds high up in the branches...spreading mistletoe to the tree's lower branches.  

According to Smithsonian magazine, "the English word for the plant is derived from a defunct Anglo-Saxon dialect. Apparently, having noticed that mistletoe often sprouts from bird droppings on tree branches, the words for dung—“mistel”—and twig—“tan”— were conjoined, and the mashup 'misteltan' evolved over time into 'mistletoe.'"

So the next time you spot a sprig of mistletoe, remember this plant has a deadly nature. And oh, did we mention? The berries are poisonous, too!  

(Not a good idea to eat them, and they can be poisonous particularly to dogs and cats.)
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Resources

Learn how to identify this plant and how to manage it.
Dwarf mistletoe

Author: Gail Hudson, Extension Communications

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