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Blueberry witches' broom

Quick facts

  • Witches' broom is caused by a rust fungus that infects both blueberry bushes and fir trees.
  • This disease causes clusters of small branches known as witches' brooms to form at the base of the plant.
  • Branches with witches' broom have small leaves and spongy, reddish bark.
  • Witches' broom is most common on blueberries in northern Minnesota planted near fir trees.
  • Since blueberry plants can’t be cured of this disease, dig up and dispose of infected plants.

How to identify witches’ broom

Symptoms on blueberries

  • Clusters of small branches form at the base of the plant.
  • Infected branches have small leaves.
  • Infected shoots have spongy, reddish bark instead of normal  green bark.

Symptoms on fir trees

  • Individual needles turn yellow.
  • Infected needles have rows of tiny white tubes. These release powdery yellow-to-orange fungal spores.
  • Infected needles often fall off.
Witches' broom
Swollen stems
Fir needle rust

How does witches’ broom survive and spread?

  • Witches' broom is caused by the rust fungus Pucciniastrum goeppertianum.
  • This fungus spends half of it’s cycle on blueberry plants and half of its life cycle on fir trees.
  • Spores are produced on infected fir needles.
  • These spores are carried by wind and infect nearby blueberry plants.
  • The fungus grows into the bark of the blueberry plants.
  • The whole blueberry plant becomes infected.
  • The fungus lives in the blueberry plant for many years.
  • Each spring, spores are produced on the blueberry witches' broom.
  • These spores then infect fir trees.

How to manage witches’ broom

  • Do not plant blueberry plants within 500 yards of fir trees.
  • It’s not possible to cure an infected blueberry plant.

Remove infected plants

  • Fungicides can’t cure the plant or prevent new infections.
  • Pruning out witches’ brooms will reduce the symptoms of the disease only for a short time. The fungus will remain in the bark of the plant and new witches’ brooms will form.
  • Infected blueberry plants should be dug up and burned, buried or composted.

Michelle Grabowski

Reviewed in 2024

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