Diseases of Potatoes: Bacterial

Bacterial Ring Rot | Bacterial Soft Rot | Blackleg | Common Scab

Bacterial Ring Rot
Clavibacter michiganensis subsp. Sepedonicus

What to look for?
Typical of late stage Bacterial Ring Rot particularly in susceptible cultivars such as Norland and Warba are wilted stems in August. Early to late August is the best time. Ring rot bacteria must pass from the old tuber via stems to the new formed tubers.

Photo: Evans

Picture description
Wilted stems; late August.

Photo: Evans

Picture description
A stem squeeze (spurge) is very important as a diagnostic technique in the absence of tuber symptoms.

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Management strategy
Plant disease-free seed tubers and follow strict sanitation procedures.

See Understanding Bacterial Ring Rot in Potatoes (Agdex 258/635-5) and Bacterial Ring Rot of Potato - Some Key Questions for more information on control of this disease.

Bacterial Soft Rot
Erwinia carotovora

What to look for?
Common under wet storage conditions, several species of bacteria may cause this condition including blackleg; potatoes are unsuitable for seed or market and are only fit for starch processing.

Photo: Evans

Picture description
Superficial lenticel infection damage on the tuber.

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Management strategy
Plant certified potatoes in well drained soils. Dig only when soil has cooled and if washing them change wash water frequently before packing. Do not wash seed potatoes.

Blackleg
Erwinia atroseptica

What to look for?

Photo: Evans	Picture description Infected stems show up with a distinct black rot.	Photo: Evans	Picture description Blackleg rotted tuber starting at the stolon end.
Photo: Evans	Picture description Blackleg on a recently planted tuber in late June.

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Management strategy
As for soft rot control, plant seed as free of blackleg as possible. Warm seed pieces 10 - 14 days before cutting or preferably plant whole seed. Follow a 3 - 4 year crop rotation and allow tubers to mature before harvest.

Common Scab
Streptomyces scabies

What to look for?
Some cultivars such as Norkotah are almost immune to scab - Fresh Market Potato Cultivar Demonstration: Disease Resistance has a list of other cultivars that have resistance to scab.

Photo: Evans

Picture description
Lesions on tuber (Warba).

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Management strategy
Avoid use of manure and use crop rotations of less than 3 years.

Potato Scab - Frequently Asked Questions

More information about bacterial diseases of potatoes can be found at Pest Management - Diseases - Bacterial. This is part of the Guide to Commercial Potato Production on the Canadian Prairies.

Photographs and information assembled and prepared for ARD by Dr. Ieaun R. Evans Agri-Trend Agrology Ltd.

For more information about the content of this document, contact Ron Howard.
This document is maintained by Shelley Barkley.
This information published to the web on November 20, 2003.
Last Reviewed/Revised on January 11, 2011.