Bacterial canker on tomatoes

Tue. Mar. 8, 2016

Click below to listen to my Garden Bite radio show:  Bacterial canker on tomatoes

My recent Yard and Garden newsletter from the University of Minnesota Extension highlights a disease that infiltrated northern gardens last year.  Bacterial canker is caused by the bacteria Clavibacter michiganensis

bacterial canker on tomato leaf
bacterial canker on tomato leaf

This bacterial pathogen is capable of infecting tomatoes and peppers, both in the Nightshade family.  In tomato, when disease is mild, the pathogen causes browning of leaf edges and fruit spots. When disease is severe, the stem cracks and becomes discolored. Leaves wilt and the entire plant may collapse and die.

bacterial canker stem

This disease is difficult to control once established, so prevention is an important management tool. Bacterial canker can be brought into the garden on infected tomato seed or transplants. The bacteria can be attached to the outside of the seed coat or carried within the seed. Infected transplants and seeds rarely show obvious symptoms of infection.  For prevention start with healthy seeds or transplants, that means buying from a reputable supplier.

There are a couple of treatments you can do at home with seed.  Actually any seed can be bleach treated.  Make a solution with one part bleach to four parts water. Add a few drops of dish soap. Add seed and allow it to sit for one minute, stirring occasionally. Make sure all sides are coated.  Pour the solution through a cheesecloth and rinse under cool water for 5 minutes.  You can plant directly or dry the seed and store it.

Hot water treatment
Soak seed in 100°F water for 10 minutes, then 122°F water for 25 minutes. Rinse in cool water for 5 minutes.

If you had bacterial canker [taken from U of MN extension]:

  • Any infected plants should be buried at the site or composted on site.
  • Throw away wooden stakes, twine, bamboo or other structures made of natural material used in the garden. These are difficult to clean because they have many pores for the bacteria to hide in.
  • Tools, metal tomato cages or other equipment made out of metal or smooth material can be cleaned with a 1:9 solution of bleach and water.


  • Remove all soil and plant debris from tools and trellises.
  • Mix 1 cup bleach with 9 cups water.
  • Wearing water proof gloves wash all tools and equipment with the bleach solution.
  • Rinse with clean water and dry before storing.
  • Do not save seed from infected plants.
  • Avoid planting tomatoes or peppers at that spot for 3 years.

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