Potato Scab - Frequently Asked Questions

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 What is potato scab?
Common Scab of potatoes is a bacterial disease. Symptoms include tan to dark brown, rough-textured lesions on the tuber surface. Scab is typically introduced into the soil by infected tubers, and will survive indefinitely in the soil. Common scab is most severe in warm, quick-drying soils and increases through a pH range of 5.2 to 8.0.

What is the economic impact of potato scab?
Common Scab is a cosmetic disease, with no effect on yield. Scab is more of a problem in table potatoes than in processing potatoes, as scab lesions are restricted to the tuber surface and peeling removes the problem. Severe scab can reduce the quantity of useable product, as more peeling is required.

Will soil amendments reduce scab incidence and severity?
It is theoretically possible to adjust soil pH to outside the pathogen’s preferred range. In reality, the quantity of amendment required to accomplish a change in pH is considerable and cost prohibitive. If the necessary adjustments were accomplished, the potato crop itself would be outside of its preferred range and yields may suffer.

What can I do to control scab?
Scab cannot be eliminated but incidence and severity can be reduced through a combination of practices.

  • Avoid introducing scab into soil by planting scab-free or treated seed.
  • Rotate to other crops for 3-4 years between potato crops.
  • Avoid susceptible crops in the rotation (root crops).
  • Green manuring (rye, millet, oat) has been reported to reduce the incidence of scab.
  • Maintain adequate soil moisture during the time of tuber formation and growth (tuber initiation starts 4-6 weeks after planting).
  • Plant more resistant cultivars.
What cultivars of potato are less likely to develop scab?
No cultivar of potato is resistant to common scab.

Potato TypeSusceptible
Moderately Resistant
RedAC Peregrine
Red Pontiac
Cal Red
Cherry Red
Dark Red  Norland
Red Cloud
Red Ruby
WhiteCal White
Irish Cobbler
AC Ptarmigan
YellowYukon Gold
Island Sunshine
RussetRanger RussetGold Rush
Russet Norkotah
Russet Burbank

Prepared by Robert Spencer, Ag-Info Centre, Alberta Agriculture & Forestry

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This information published to the web on June 2, 2003.
Last Reviewed/Revised on December 13, 2016.