Bacterial blight of coriander

Bacterial blight is an important disease of coriander. These pages summarise the latest information relevant to UK growers, including the symptoms and biology of the disease, and available methods of control.

This information was last updated in 2023.

An important disease of coriander

Coriander (Coriandrum sativum) is one of the major field-grown herb crops in the UK and it is grown at high densities for fresh leaf production. Bacterial blight or leaf spot has been a recurring problem on field-grown crops and can also occur in pot-grown production.

The disease was first seen in the UK in 1967, but was not formally reported in scientific literature until 1980.

Key points

• Bacterial blight of coriander is caused by Pseudomonas syringae Coriandricola (Psc).
• Brown angular leaf spots with water-soaked margins and yellow haloes coalesce to form larger blighted areas.
• The primary source of inoculum is seed.
• Local plant-to-plant spread is mainly via water-splash or aerosols from rain or irrigation.

Recommendations for growers

• Confirm that seed has been tested for Psc and meets the minimum recommended health standard of <0.03% with a test sensitivity of 900 CFU.
• Clean/disinfect drilling equipment between seed lots.
• Do not enter crops when wet.
• Minimise the movement of machinery and people within and between crops.
• Clean and disinfect machinery and equipment, clothing and footwear when moving between crops.
• Incorporate or destroy crop debris as soon as possible after harvesting.
• Do not grow crops in the same field more than once every two years.
• Be aware of the potential for cross-infection with parsley.
• Inspect parsley for signs of bacterial disease - do not assume that leaf spots on parsley are caused by Septoria.

Recommendations for seed suppliers

• Take precautions to avoid cross-contamination between seed lots via dust/debris.
• Vacuum, clean and disinfect machinery, storage areas/bins between seed lots.
• Test seed prior to cleaning and
• To ensure accuracy, it is important that samples for seed testing are obtained according to the International Rules for Seed Testing.
• Discard or hot-water treat seed lots with infection levels >0.03%.
• Re-test treated seed.
• Process/clean the cleanest seed first.
• Consider applying a more stringent seed health standard for seed used for seed crops.
• Consider hot-water treatment of seed used for seed-crops regardless of health status.
• Consider testing parsley seed for Pseudomonas syringae pv. coriandricola.

Symptoms and biology

Find out more about the symptoms and biology of this key disease.

Prevention and control

Coriander bacterial blight is very difficult to control once disease has become established in a crop and symptoms are widespread. The most effective way to manage the disease is to use ‘clean’ seed which has been tested and shown to meet minimum seed health standards.

Author

Dr Steven J. Roberts, Plant Health Solutions Ltd., Warwick, UK.