Tomato Bacterial Canker

Tomato Bacterial Canker

Author: Matthew DeBacco

Reviewed by: Shuresh Ghimire, Ph.D.
Associate Extension Educator
Extension Vegetable Specialist

Date of Publication: 

Introduction

Tomato bacterial canker is caused by the bacterium Clavibacter michiganensis subsp. michiganensis (Cmm). It is the most destructive disease of tomatoes in our region.  The disease can substantially reduce yield, especially when it severely affects leaves early in the growing season, leading to wilted and stunted plants, delayed fruit maturity, cankers, and characteristic bird's eye spots on fruits.  The impact on fruit quality is significant, causing disfigurement that reduces marketability, particularly for the fresh market. This can lead to significant yield losses, especially in greenhouses and high tunnel production. 

hand holding a tomato leaf attached to a plant. The top of the leaves have light streaking.
Wilting of leaves that may be unilateral and the formation of light streaks up and down the outside of the leaf midrib, petiole and stem are symptoms of bacterial canker. The streaks may open to form cankers. Photo Credit: University of Florida.

the inside of a tomato stem with lots of browning.
Bacterial canker of tomato: brown streaks in the vascular system when cut lengthwise. Stem cankers, which are splitting and browning of the stem, may develop, particularly in fields. The pith (center of the stem) can become discolored, grainy or pitted. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org.

ripe red tomato with small yellow raised spots
Bacterial canker symptoms on a ripe fruit. Photo Credit: Cornell University.

top image is green cherry tomato with raised bumps still on the branch. bottom left image is individual green tomato with raised white spots. bottom right image is an unclose view of those spots under a microscope.
Bacterial canker of tomato: Symptoms on fruit appear as raised, white spots with tan or brown centers surrounded by a white halo, resembling a bird's eye, also known as "bird's eye spot". Photo Credit: Rubio, I. et al. (2021). Current knowledge and future challenges. Plant Disease, 105(5), 1096–1113.

browning leaves on a tomato plant
Bacterial canker of tomato causes necrosis (browning) at the leaf margins, often with a yellow border and upward curling. Photo Credit: D. Egel, Purdue University.

Symptoms

Leaves: Initial small, dark spots may develop into larger areas of browning or scorching along the margins, often with a yellow halo. Leaves may wilt, curl upwards, and eventually die.  There may be one side of the leaflet exhibiting wiltingwhich may be more commonly seen in greenhouses. Yellow to tan patches may form between veins, with brown edges and a yellow border, and veins can become dark and sunken, though this is not always visible. 

Stems: Cankers or lesions may form with brown streaks in the vascular system, which are evident when cut open, and stem splits may form long, brown cankers. Yellow, sticky fluid may emerge when squeezed, indicating infection.   

Fruits: Small (1/4” diameter), raised, dark brown lesions surrounded by a white halo, known as "bird's eye spots," andreducing marketability. 

Host Crops: Solanaceae family (Tomatoes, Peppers, Eggplant) 

Identification of Disease

Tomato bacterial canker affects tomato plants by inducing wilting, defoliation, desiccation, skin cankers, and reduced fruit yield and quality, ultimately leading to plant death. Research suggests that Cmm enters the tomato through natural openings, wounds (roots, stem, or fruits), or from infected seeds, multiplying in the cells responsible for water transport and producing a slimy biofilm that aids in colonization and movement. Symptoms can develop in approximately a week under favorable conditions, such as temperatures between 77°F - 86°F. 

Not to be Confused with:

Bacterial Speck- Smaller spots and not systemic 

 

Management

At this time there are no known tomato varieties with resistance to bacterial canker. 

 

Cultural:

  • Rotate out of tomatoes for at least 2 years
  • Plant certified pathogen-free seed stock 
  • Do not save seeds from infected plants 
  • Hot water seed treatment (122F for 25min.) 
  • Disinfect stakes before reusing 
  • Avoid working in fields when plants are wet 
  • Clean pruning tools and any plant supports 

            Chemical:

            • Use copper or streptomycin on plants before transplanting 
            • Chemicals by themselves are not sufficient to control the disease once it is established 
            • See  New England Vegetable Managment Guide for a more comprehensive list of sray products 

                 

                References

                Cornell University. (n.d.). Bacterial canker. Cornell Vegetables. https://www.vegetables.cornell.edu/pest-management/disease-factsheets/bacterial-canker/ 

                 Egel, D. S. (2018, May 17). Tomato bacterial diseases: Bacterial canker. Vegetable Crops Hotline. https://vegcropshotline.org/article/tomato-bacterial-diseases-bacterial-canker/ 

                Rubio, I., Motisi, N., Audeguin, L., Bertrand, M., Chastagner, A., Deberdt, P., Husson, O., Loiseau, M., Marie, L., Merlin, I., Meyer, J.-B., Pruvost, O., & Vallance, J. (2021). Bacterial canker of tomato: Current knowledge and future challenges. Plant Disease, 105(5), 1096–1113. https://doi.org/10.1094/PDIS-08-20-1732-FE 

                University of California Agriculture and Natural Resources. (n.d.). Bacterial canker. UC IPM Online. https://ipm.ucanr.edu/agriculture/tomato/bacterial-canker/ 

                University of Florida, Institute of Food and Agricultural Sciences. (n.d.). Bacterial canker. U-Scout: Tomato. Retrieved July 2, 2025, from https://plantpath.ifas.ufl.edu/u-scout/tomato/bacterial-canker.html 

                University of Minnesota Extension. (n.d.). Bacterial canker of tomato. https://extension.umn.edu/disease-management/bacterial-canker-tomato 

                 

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