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Broom Gall Mite

Pest

Broom gall mite is a tiny pest that causes abnormal, dense growths on the stems of Scotch broom plants. These growths, known as galls, can weaken the plant and ruin its natural shape over time.

Symptoms by part

Stems

Look for dense, tangled clusters of stunted twigs and buds that resemble a small broom or a bird nest. These galls are often woody and can range from the size of a marble to a golf ball.

Causes

  • The microscopic mite Aceria genistae feeding on the meristematic tissue of the plant.
  • Wind currents carrying the mites from nearby infested plants to healthy ones.
  • The presence of existing infested broom plants in the immediate vicinity.

Could be confused with

  • Witches broom caused by fungi · Fungal witches broom often shows signs of powdery or fuzzy growth on the stems, whereas mite galls are strictly woody and lack fungal spores.
  • Normal plant growth · Normal growth is symmetrical and follows the plant's natural branching pattern, while galls are chaotic, dense, and lack proper leaf development.

Treatment

  1. Prune away all visible galls during the dormant season to remove the mite population before they become active.
  2. Sterilize your pruning shears with rubbing alcohol between every single cut to prevent moving mites to healthy branches.
  3. Dispose of all pruned material by burning it or sealing it in a bag for trash collection, never composting it.

Without chemicals

  • Physical removal of galls by pruning is the most effective method.
  • Ensure proper plant spacing to reduce the likelihood of windborne mites landing on neighboring plants.

Chemical options

  • Sulfur, apply as a spray to the foliage during the early stages of the warm growing season to deter mite movement, follow the label.

Preventing it

  • Inspect new plants thoroughly for any signs of abnormal growth before bringing them into your garden.
  • Remove and destroy any wild or neglected broom plants nearby that show signs of infestation.
  • Keep plants healthy with appropriate watering and soil conditions to help them withstand minor infestations.

Season

The warm growing season, when the mites are most active and migrating between shoots.

Spread risk

Moderate

Severity

Moderate

When to act

Act as soon as you spot the first galls to prevent the infestation from spreading to the rest of the plant. If the plant is heavily covered in galls, it is best to remove and replace it entirely.

Think it's Broom Gall Mite?

This guide covers the general picture. Pocket Botanist looks at your actual plant from a photo and tells you what's really going on, how serious it is, and what to try first. Identification and a health check are free.

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Questions people ask

Can I just prune the galls off and leave the plant?
Yes, if the infestation is light, pruning the galls and disposing of them properly can save the plant.
Will the galls go away on their own?
No, the galls are permanent woody structures and will not disappear without physical removal.
Are these mites harmful to other plants in my garden?
Broom gall mites are highly host specific and generally only affect broom species.

Plants it affects

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This guide was generated with AI and is general information, not horticultural advice. Read about how we build these guides.