VIDEO: Witchesโ broom sounds like something for Halloween, but for trees, it is not part of a costume. The broom, a dense mass of branches, is the result of dwarf mistletoe, a parasitic plant impacting Montana forests.
โA lot of times infected trees look really green and healthy, but it’s actually just the mistletoe, the parasitic plant,โ said Amy Gannon, who runs the Forest Pest Management Program for the Montana Department of Natural Resources & Conservation (DNRC).
Every species of Montana conifer, except Ponderosa pine, has been targeted by its own specific mistletoe. The infection starts small, then grows for years, or even decades, slowly choking the tree beneath it.
โThey have to have a living host and they draw the nutrients from the host tree,โ Gannon said. โThat’s robbing the tree of all the nutrients, and the rest of the tree is dying. So, the top of that tree is dying.โ
As the infection progresses, the parasite becomes more and more visible. As hormonal changes occur in the tree, witchesโ brooms grow large, protruding out in heavy, dense clusters. The infection spreads, attacking more than one tree in a stand.
โIt’s important to recognize that these plants are raining seeds down on the understory,โ Gannon said. โThey shoot seeds, and they can go 20, 30 feet, and then they’ll stick on the understory.โ
