Scab in Carrots
Scab in Carrots

Casual Agent

Scab is caused by Streptomyces scabies, a bacterial pathogen that is present in soils where potato is the predominant crop. Other root crops such as beets, turnips, parsnips, radishes, and carrots may be affected if grown in these soils.


S. scabies can cause a variety of symptoms on root crops including both pitted and raised lesions on the root portion of the plant . There are no symptoms displayed aboveground.

Disease Cycle

S. scabies causes infections when the air temperature reaches 80O F. It is unusual bacterium in that is has filamentous growth, similar to fungi. The filaments can break off, forming survival structures in plant debris in the soil. S. scabies infects the plants by growing in between and through the plant cells of the host.


  • Use tolerant or resistant cultivars when available.
  • Use certified, disease-free seed.
  • Rotate Crops. Implementing crop rotation between potatoes, carrot, radishes, and turnips with non-susceptible crops such as corn, alfalfa, and small grains.