Common scab or corkey scab

Common scab or corkey scabStreptomyces scabies


  • Corkiness of the tuber periderm is the characteristics symptoms.
  • 1/4 inch into the tuber surface are russette appearance.
  • Slightly pitted on the infected tuber. Light brown to dark brown lesion appears on the infected tuber.
  •  Affected tissue will attract insects.


Identification of pathogen:

Mode of spread and survival:
  • It attacks cabbage, carrot, egg plant, onion, radish, spinach and turnip.
  • The causal organism perpetuates in soil and infects the crop every year.
  • Infected potato tubers serve as the main source of long distance spread of the disease.
  • The pathogen may survive passage through digestive tract of animals and hence it may spread with farm yard manure.



  • Only scab free seed potatoes should be planted as this will help in checking the spread of the inoculum and infection to be subsequent crop.
  • Infection of the seed tubers can be removed by 1.5hrs dip in mercuric chloride 0.1% solution or by 2h dip in 1 part formaldehyde in 240 parts of water.
  • This disease can be reduced by soil application of PCNB at the time of planting. Four to six years crop roation with alfalfa satisfactory under irrigated conditions.
  • The disease incidence can be effectively reduced by green manuring the fields before planting potatoes.
  • Common scab is severe in alkaline soil and application of alkaline fertilizers like calcium ammonium nitrate should be avoided.
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