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UC Pest Management Guidelines

Bacterial ring rot symptoms in tubers.


Bacterial Ring Rot

Pathogen: Clavibacter michiganensis subsp. sepedonicus

(Reviewed 8/07, updated 8/07)

In this Guideline:


Foliar symptoms of bacterial ring rot generally appear at mid-season or later. Yellow areas develop on leaf margins or between veins and later turn brown, giving the leaves a burned appearance. Plants with advanced symptoms show vascular discoloration and milky, viscous bacteria may be forced from cut stems. In tubers, symptoms may occur before harvest or in storage. Rot begins as a brown necrosis in the vascular ring and progresses to surface. Cracks may appear on surfaces of tubers, which are frequently nothing more than hollow shells.


The bacterial ring rot bacterium overwinters in infected tubers. It does not live freely in the soil, but it can survive for long periods as a dried slime on harvesting and grading machinery, sacks, etc. A wound is required for infection and spread occurs most commonly when seed is cut.


Use only certified seed tubers, rotate out of potatoes at least one year, and follow strict sanitation procedures when cutting seed. Periodically disinfect cutting tools in a 1% solution of calcium hypochlorite. Use of whole-drop seed will minimize spread. Cup-type planters will spread the pathogen less than pick-type.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
R. M. Davis, Plant Pathology, UC Davis
J. Nuñez, UC Cooperative Extension, Kern Co.
B. J. Aegerter, UC Cooperative Extension, San Joaquin Co.
Acknowledgment for contributions to the disease section:
C. Smart, Plant Pathology, UC Davis

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