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Witches’ Broom

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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