Leafy gall

Leafy gall is a bacterial disease of the stems and roots of many herbaceous plants. Infection with this disease causes dense clusters of distorted leafy shoots.

Leafy gall on wallflower. Image: RHS, Horticultural Science

Quick facts

Common name Leafy gall
Scientific name Rhodococcus fascians
Plants affected Mainly herbaceous plants
Main symptoms Distorted leafy shoots
Caused by Bacterium
Timing Generally summer, but depends on plant affected

What is leafy gall?

Leafy gall is a disease caused by the bacterium Rhodococcus fascians, which enters the plant through wounds in roots or stems and stimulates the plant tissues to grow in a disorganised way, producing dense clusters of distorted, leafy shoots.

The disease is not common and seldom damaging. In gardens, Chrysanthemum, Dahlia, Lathyrus (sweet pea), Nicotiana, Pelargonium (geranium) and strawberries are among the plants most commonly attacked.  Expect this disease in summer.

Symptoms

You may see the following symptoms:

  • dense clusters of distorted leafy shoots, often close to ground level
  • witches broom
  • bud proliferation
  • reduced lateral root development

Control

Non-chemical control

Leafy gall is seldom serious enough to warrant control, but if it is troublesome, carefully sterilise pots, surfaces and tools to help eliminate the bacterium, Rhodococcus fascians. All potentially-contaminated growing media (potting compost) should be destroyed (or sent for council composting).

Chemical control

There are no chemicals available for the control of leafy gall.

Biology

Infection by Rhodococcus fascians (formerly Corynebacterium fascians) has a similar effect to that of crown gall. Instead of galls, the host tissues produce dense clusters of distorted, stunted shoots at ground level. The bacterium disrupts normal plant hormone levels, in particular auxins and cytokinins, causing the symptoms observed.

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