Potato Scab - Frequently Asked Questions

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.

Potato Type	Susceptible	Moderately Resistant
Red	AC Peregrine Red Pontiac Sangre	Cal Red Cherry Red Chieftain Caribe Dark Red  Norland Norland Nordonna Red Cloud Red Ruby Viking
White	Cal White Shepody Irish Cobbler	AC Ptarmigan Eramosa Kennebec Superior
Yellow	Yukon Gold Bintje	Adora Agata Albina Dali Island Sunshine Penta Provento Sante
Russet	Ranger Russet	Gold Rush Russet Norkotah Russet Burbank

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