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Bacterial canker of tomato

Quick facts

  • Bacterial canker is primarily important on tomato.
  • This bacterial disease is suspected to be seedborne, and can survive in solanaceous weeds and decaying plant tissue.
  • Disease symptoms can look different in the field than in high tunnels.
  • Bacterial canker can persist in the soil for a long time, so focus on prevention.
  • Transplant production is the key time to manage bacterial canker.

How to tell bacterial canker from other issues

Stem canker from bacterial canker of tomato
  • Symptoms vary with age of plant, type of infection, environment and other factors. This disease can be difficult to diagnose based on symptoms alone. 
  • Confirm diagnosis by sending a plant sample to the UMN Plant Disease Clinic.


  • Small, white, raised spots may form on leaves.
  • Leaf edge discoloration and wilting. 
  • Seedling completely wilts and dies.


Leaf infection of bacterial canker
  • Yellow to tan patches form between veins. Edges of leaf turn brown, with a yellow border.
  • Veins on the leaves and petioles can become dark and sunken.This symptom does not always show up.
  • Lower leaves wilt, often only on one side. 
  • Entire plant may collapse and die.


Internal stem discoloration caused by bacterial canker.
  • Brown streaks can be seen in the vascular system when the stem is cut open.
  • Stem splits, forming long, brown cankers.
  • Yellow sticky fluid may emerge from cut stem when squeezed.


Fruit infection of bacterial canker
  • Fruit may have small (1/4 inch), raised, white spots with tan or brown centers (called bird's eye spot). 
  • Fruit surface may appear netted or marbled.


Wilt caused by bacterial canker
  • The disease is caused by the bacterial pathogen Clavibacter michiganensis subspecies michiganensis.
  • Warm temperatures (75 to 90°F), high moisture or relative humidity encourage disease development and spread.
  • Infected seed or transplants spread the bacterial canker pathogen long distances and introduce it to new areas.
  • The disease easily spreads between seedlings in a transplant production greenhouse through growers' hands, equipment, and during pruning and trellising of plants. One infected seed can result in many infected transplants, through which the disease can become established in high tunnels or fields.
  • Transplants may be infected yet not initially show symptoms. In the field, infected transplants often die and secondary spread is limited or of little economic impact.  In tunnels or greenhouses, the disease easily spreads between transplants and between older plants through practices like pruning and staking. This can result in severe symptoms and yield loss.
  • The pathogen survives up to three years on non-decomposed tomato plant debris and can survive for several months on stakes and equipment, thereby readily infecting tomatoes planted in the same tunnel the following season.

Managing bacterial canker in home gardens

Look for leaves with spotting, especially during periods of wet, humid weather. Remove leaves with symptoms.

Cultural controls

  • Plant tomatoes where no tomatoes, potatoes, peppers or eggplants have been for the past 3-4 years.
  • If starting your own seeds, choose seeds from a reputable supplier
  • If buying transplants, inspect transplants and choose plants without spots or discoloration
  • Keep tomato leaves as dry as possible. Water with drip irrigation or a soaker hose. Water in the morning so leaves dry quickly in the sun.
  • Space plants so that air flows between them. Staking or caging tomato plants helps, though make sure to clean and sanitize tomato stakes and cages each year.
  • Remove or bury plants at the end of the season

Managing bacterial canker on farms


Authors: Marissa Schuh, horticulture IPM Extension educator, Michelle Grabowski and Angela Orshinsky

Reviewed by Natalie Hoidal, Extension educator

Reviewed in 2024

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