Xanthomonas black rot of vegetable brassicas

Black rot is an important bacterial disease of vegetable brassicas. These pages summarise the latest information on the symptoms and management of this disease relevant to UK growers.

This information was last updated in 2023.

An important disease of brassicas

Black rot (Xanthomonas campestris pv. campestris) can cause complete crop loss in vegetable brassicas . More commonly under UK conditions it causes significant reductions in marketable yield particularly in autumn and winter crops.

In addition to direct yield losses the disease also leads to increased labour costs as a result of additional time needed for trimming and harvesting. This can result in crops being abandoned.

Key points

• Black rot of brassicas is caused by the bacterium Xanthomonas campestris campestris.
• Symptoms are most commonly seen as yellow or necrotic V-shaped lesions with blackened veins.
• Infested seeds are the primary source of inoculum and means of long-distance dissemination.
• Local plant-to-plant spread is mainly via water-splash or aerosols from rain or irrigation.
• Rapid spread during plant-raising means that low levels of seed infestation can result in significant disease levels in field crops.

Recommendations for brassica growers

• Confirm that brassica seed has been tested for Xanthomonas to an appropriate standard.
• Request information from seed suppliers on the effective tolerance standards applied (e.g. number of seeds tested).
• Check that transplant suppliers only use tested seed and have appropriate hygiene policies.
• Don't dip transplants before planting.
• Clean and disinfect machinery and equipment, clothing and footwear when moving between crops.
• Post-harvest cultivations should aim to encourage rapid breakdown of crop residues.
• Use a non-brassica break for two years after field outbreaks of black rot.

Recommendations for brassica plant-raisers

• Confirm that all brassica seed coming on to the unit has been tested for Xanthomonas to an appropriate standard.
• Request information from seed suppliers on the effective tolerance standards applied (e.g. number of seeds tested).
• Module trays should be cleaned and disinfected before each use.
• Clean and disinfect sowing equipment before each new batch of seed.
• Clean and disinfect glasshouses/bays before each batch of transplants.
• Separate batches of plants grown from different seed lots as much as possible.
• Minimise the use of overhead irrigation.
• Consider the use of sub-irrigation systems.
• Clean and disinfect equipment between batches.
• Don't water transplants in stillages.

Symptoms and biology

Find out more about the symptoms of this disease and how to identify it, as well as its epidemiology.

Prevention and control

Black rot is very difficult to control once disease has become established in a crop and symptoms are widespread. The best means of control is prevention through the use of clean seed and transplants.