Crown gall

Agrobacterium tumefaciens

A soil bacterium that makes plants grow lumpy, tumor-like galls, usually at the stem base or on the roots, soft at first then hard and woody.

Bacterium Disfiguring Soil-borneSpread in waterSpread on tools & hands Spreads to neighbors

What you'll see

Rounded, irregular, tumor-like galls swell at the crown near soil level or along the roots and stems.
The galls start pale, soft and spongy, then harden, darken and turn corky and woody.
They can range from pea-sized to fist-sized, sometimes clustered together.
A heavily galled young plant may grow weakly and lack vigor, though many plants carry galls with little harm.

Why it happens

A soil bacterium that enters through wounds at the stem base or roots and hijacks the plant’s cells into forming galls. Grafting cuts, transplanting damage, hoeing nicks and insect wounds all let it in.

It follows wounding, so it is worst on freshly planted or grafted stock and in wet ground where the bacterium is plentiful and moves easily.

Treating it

On established woody plants galls are usually harmless and best left alone.
Cut galls out of a valued plant only if you can do so cleanly, disinfecting the blade afterwards.
Dig up and destroy a badly affected young plant that is failing to establish.
Do not replant a susceptible plant in the same spot without improving drainage first.

Keeping it away

Handle roots and stems gently at planting to avoid wounds at the base.
Buy healthy stock and reject any plant with galls at the graft or crown.
Improve drainage, as the bacterium spreads readily in wet soil.
Disinfect knives and secateurs between plants, especially when grafting or taking cuttings.
Avoid careless hoeing and strimming around the stem base.

Who gets it

A very wide range of plants — roses, fruit trees, cane fruit, grapevines and many woody ornamentals.