Guide

Look closerPlants

Witches' brooms: dense twig clusters on tree branches

December to March

Witches' brooms are dense clusters of many short twigs growing from one spot on a tree branch. Mites, fungi, phytoplasmas, mistletoe, or a bud mutation can cause them, and on trees like hackberry they are easiest to spot once the leaves are down.

Why this time of year

With the leaves off, brooms that leaves can hide in summer stand out in bare crowns. On hackberry, the damage is most noticeable in the winter months when leaves are absent.

How to notice it

  1. Standing on the ground, scan the crowns of bare deciduous trees for a tight bunch of short twigs all growing from one spot on a branch.
  2. Check hackberry trees, where brooms are especially common. Maple, willow, cherry, pine, and spruce can carry them too.
  3. Count the brooms on one tree. A bud mutation usually makes just one broom on a tree, while brooms caused by living things can be one or many, scattered through the tree.
  4. Look from the ground only. There is no need to climb, and no need to break a broom off.

Try this with kids: Stand under a bare tree and look up. Can you find a spot where lots of little twigs grow out of one place, like a broom? How many brooms can you count on that one tree?

Word to know: “Phytoplasma”: a tiny bacteria-like organism.

Safety

  • Look from the ground; do not climb trees or reach up to pull brooms down.

Sources

  • hyg.ipm.illinois.eduIllinois Extension: dense clustering of shoots from a single point; caused by insects, fungi, viruses, or phytoplasmas depending on host; especially common on hackberry; 'most noticeable in the winter months when leaves are absent'; rarely threatens tree health. (Certificate error in WebFetch; read via curl -k.)
  • yardandgarden.extension.iastate.eduIowa State Extension: hackberry brooms easy to spot with no leaves; cause not known with certainty.
  • yardandgarden.extension.iastate.eduIowa State Extension: hosts include hackberry, maple, willow, pine, spruce; causes fungi, phytoplasmas (bacterial-like organisms), mites, aphids, mistletoe; usually just one broom per tree when the cause is a genetic mutation.
  • extension.psu.eduPenn State Extension: dense twiggy mass from a single bud or shoot; environmental/organism or spontaneous genetic mutation; may grow for many years.
  • extension.psu.eduPenn State Extension: hackberry broom, many short twigs close together from a swelling; powdery mildew plus eriophyid mite.
  • extension.umd.eduUniversity of Maryland Extension: causes fungi, viruses, phytoplasmas, eriophyid mites, mistletoe, environmental damage, mutation; Taphrina fungi cause witches' broom of cherry. (Read via curl -k.)
  • apps.extension.umn.eduUniversity of Minnesota Extension: hackberry witches' broom damage most noticeable after leaves have fallen.

Checked against these sources on November 3, 2026.

In the guide for December, January, February, March

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