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Witches’ Brooms

If you’ve ever seen a tree or shrub that looks like its growth has gone haywire in one particular spot, you may have come across a phenomenon called Witches’ Broom.  Witches’ Broom is defined as an “abnormal brush-like cluster of dwarfed, weak shoots arising at or near the same point.” This deformed mass of twigs and branches occurs in response to pathogens and insect pests (mites, aphids, nematodes, fungi, viruses, bacteria and phytoplasmas (parasitical bacteria)) as well as stressful environmental conditions.

Susceptible plants include alder, serviceberry, birch, cherry, elm, fir, hackberry, honey locust, juniper, red cedar, mulberry, oak, ash, willow and spruce, among others. Often Witches’ Brooms are relatively small — a foot or so in diameter. The one pictured required multiple years of growth to reach its current size.  Most Witches’ Brooms are not fatal, just disfiguring.

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6 responses

  1. Alice

    It might be disfiguring, but the broom on the top is very interesting looking! I’ll be curiously looking out for one.

    November 26, 2021 at 8:43 am

  2. diane bartholomew

    witches brooms make very interesting indoor decor, au natural or painted!

    November 26, 2021 at 8:53 am

  3. Rachel

    Highbush blueberries are the alternate host for the pathogen that causes witches broom in balsam fir. This is a problem for those of us in the North where Fir is abundant. While the blueberries can deal with the broom for a several -or even many-years and still be productive, eventually it kills them or just makes them unproductive. I’m starting to grow more raspberries now that most of my highbush blueberries have succumbed.

    November 26, 2021 at 10:19 am

    • Jean Clark Townsend

      The same thing happened to us. When I think “witches’s broom” I always think “blueberries.”

      November 27, 2021 at 6:05 pm

  4. Pat Nelson

    On my property, I’ve had witches broom on a highbush blueberry and a winterberry. The blueberry is in the shade under some hemlocks, so it never fruited anyway, and it migt have died by now. The winterberry is quite close to some birches.

    November 26, 2021 at 2:27 pm

  5. There is SO MUCH witches’ broom on the spruce on Isle au Haut. I didn’t know the connection to high bush blueberries. I wonder if you can cut it out, or if it is systemic.

    November 26, 2021 at 9:02 pm

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