Crown gall
A bacterial disease that forms rough, woody, tumour-like swellings at the base of the stem and on roots of many fruit and ornamental plants.
Also known as: Bacterial gall
Symptoms and identification
Round, rough, corky growths 1 to 5 cm or larger form at the crown, on roots and sometimes on canes and stems. Young galls are pale and soft, and they darken and harden with age. Affected plants grow slowly, look stunted and may wilt in dry spells.
Causes
The bacterium lives in soil for years and enters through wounds from pruning, grafting, insects, frost, cultivation or transplanting. It is often brought in on infected nursery stock.
Organic treatment
There is no cure. Remove and bin heavily galled plants and the soil around the roots. On large trees, prune small galls on branches and disinfect tools after each cut.
Prevention
Buy plants with a clean root and crown, avoid wounding stems at the soil line, disinfect pruning tools, and plant in soil that has not grown susceptible plants before.
Chemical treatment (use with care)
There is no chemical cure for established galls. A biological dip using Agrobacterium radiobacter strain K84 is available in some countries to protect healthy roots before planting.