Scab
Steptomyces scabies
Pathogen
Bacterium
Hosts
Carrots
Symptoms
Horizontal blackened, corky lesions on the root surface which can be either raised or sunken. These can arise in areas where lateral roots develop or where roots are punctured.
There are no visible symptoms on plant leaves.
Can also be a problem on other root crops such as potatoes, swedes, turnips, radish and beetroot.
Development
An organism related to bacteria but like fungi produces mycelium which can invade roots.
The scabs produce spores which exist as part of the soil microflora.
Favourable factors
Hot, dry summers on light sandy alkaline soils.
Importance
Does not adversely affect crop yield but does impact on quality and marketability.
Control
Irrigation
Avoid applying lime to scab infested fields before sowing.
Rotation with non-root crops may help.
Carrot scab (Photo T. Lacey)
Close up of carrot Photo T. Lacey)
