One popular inquiry I receive during the winter months concerns odd growths on conifer trees, especially fir and spruce. These are called witch's brooms. They are a form of fasiculation or plant cancer. They may have the appearance of a small tree growing inside a large one, or a ball of twigs. Either way, they comprise a bundle of twigs with short internodes.
A series of causes may be identified: most of which kill the terminal bud of the affected branch. Fungal infections, mite attacks, dwarf mistletoe or even environmental conditions may all result in the formation of this curiosity on a variety of leafy trees or conifers. In our spruce and fir it is almost always the Dwarf Mistletoe (shown) to blame.
This tiny parasite produces no chlorophyll. Rather it is a true parasite, living off the avails of healthy trees. Usually, the host trees continue growing, but with the brooms attached.
Does anybody have a picture of a witch's broom they would like to share?
Dwarf Mistletoe (Arceuthobium pusillum) Photo by Sean Blaney
witch's-broom, Photo by Marian Munro
A series of causes may be identified: most of which kill the terminal bud of the affected branch. Fungal infections, mite attacks, dwarf mistletoe or even environmental conditions may all result in the formation of this curiosity on a variety of leafy trees or conifers. In our spruce and fir it is almost always the Dwarf Mistletoe (shown) to blame.
This tiny parasite produces no chlorophyll. Rather it is a true parasite, living off the avails of healthy trees. Usually, the host trees continue growing, but with the brooms attached.
Does anybody have a picture of a witch's broom they would like to share?
Dwarf Mistletoe (Arceuthobium pusillum) Photo by Sean Blaneywitch's-broom, Photo by Marian Munro
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