Pest Management - Diseases - Bacterial

Return to the Guide to Commercial Potato Production on the Canadian Prairies..

Potato plants are susceptible to a wide variety of diseases that can severely reduce yield, quality and storability of tubers. Diseases can occur in the field or in storage and are caused by infectious bacteria, fungi, viruses and other related organisms.

Most infectious potato diseases can be controlled using certified seed, proper sanitary practices, crop rotation, and pesticides. The following are the most serious diseases of potatoes in the Prairies. Consult your provincial Guide to Crop Protection for a list of chemicals registered for control of potato diseases.

Bacterial Ring Rot

Bacterial ring rot is a highly infectious disease caused by the bacterium Clavibacter michiganensis, formerly known as Corynebacterium sepedonicum. This disease can cause serious losses and is a designated pest in provincial Plant Disease Acts. The Canadian Food Inspection Agency has a zero tolerance for bacterial ring rot in seed potatoes.

Internal symptoms of bacterial ring rot Courtesy of Manitoba Agriculture, Food and Rural Initiatives

Foliar symptoms of the disease vary with the potato variety. Symptoms are not always expressed or may be masked by other stresses on the plant. Ring rot may cause wilting of the lower leaves. Leaves on infected plants yellow and the outer edges may roll up and later become brown and brittle. The lower stem of infected plants will exude a milky ooze when cut and squeezed. Tuber symptoms are noticeable as a cheesy cream-colored liquid that oozes from the vascular ring when tubers are cut at the stem end and squeezed. As the rot progresses, the vascular ring breaks away from the rest of the tuber. Secondary rot organisms may also infect the tubers and make it difficult to distinguish the ring rot symptoms. Severely infected tubers turn dark brown or black and completely rot away inside.

During seed cutting, bacteria from infected tubers are smeared on the cutting knives, consequently healthy seed pieces become infected. Ring rot bacteria can survive for five years in dried potato stems and for two years on dry burlap, plastic or plywood surfaces. The bacteria however, live only a short time in soil and are normally killed between fall and winter if all plant debris is ploughed down. Ring rot bacteria can over-winter in infected tubers that survive the winter in the field or in cull piles.

Control strategies:

• Plant certified seed
• Thoroughly clean and disinfect equipment, tools, trucks and storages with a quaternary ammonium disinfectant (see Sanitation, Handling and Storage of Seed Lots), or limit movement of machinery and personnel between operations (especially seed)
• Dispose of any crops infected with ring rot
• Dispose of mildly infected crops by processing out-of-field rather than out-of-storage
• Sprout inhibit infected potatoes, so they will not grow
• Plant crops other than sugar beets after potatoes
• Plough under infected potato debris or unharvested potatoes prior to winter
• Allow at least one year before replanting potatoes in an infested field
• Dispose of all used potato sacks or bags
• Destroy cull piles by freezing or burying

• Prior to planting, warm seed tubers to approximately the same temperature as the soil, to reduce condensation on the tubers, which promotes rot
• Clean and disinfect seed cutters, handling equipment, and trucks
• Minimize mechanical damage during harvesting, handling, and packing operations
• Avoid frost injury and properly dry frozen tubers in storage. (See section 3.9.4 Special Storage Problems).
• Use clean water that is changed often or chlorinated during washing operations
• Remove potato cull piles, discarded vegetables and plant refuse from fields and storage
• Control other tuber diseases
• Prevent condensation water from forming on tubers by ensuring that cold tubers are ventilated with cool air.

• Plant blackleg-free, certified seed
• Clean and disinfect seed cutters, handling equipment, and trucks
• Plant in warm soil
• Prevent stem damage during cultivation, roguing and harvesting
• Rogue diseased potato plants, ensuring they do not come into contact with other plants in the field (see section 6.3.2 Disease Prevention, Roguing and Insect and Irrigation Management).

• Plant disease-free seed into non-infested soil
• Beginning at tuber initiation, maintain high soil moisture for 4-6 weeks
• Increase time between potato crops to 3-4 years
• Plant early, harvest early
• Plant less susceptible cultivars such as Russet Burbank

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