Bacterial Canker of Greenhouse Tomatoes

Bacterial canker (caused by Clavibacter michiganensis pv. michiganensis) is a disease of tomatoes that shows up occasionally in BC greenhouses. It is important to watch for early signs of the disease, get a proper diagnosis, and take immediate action if it is found in your greenhouse.

Bacterial Canker Symptoms:

Seedlings – If infected during the seedling stage, lesions may develop. These are cream-to-white, raised blisters or pustules on leaves and stems, which resemble oedema (a physiological condition).

Plants – Infected tomato plants begin to wilt, possibly just the lower leaves or just above the portion of the stem that is infected. It may appear that leaflets on only one side of a leaf are affected. Light yellow to brown streaks may or may not be seen on the stems (Figure 1). When affected stems are split open lengthwise, a thin, yellow to reddish-brown discolouration of the vascular tissue may be observed. Wilted leaves may also have marginal necrosis (brown, dead tissue) (Figure 2.) As the disease progresses, more wilting and leaf necrosis develop. Light streaks on stems darken with age. The pith in infected stems turns dry, brown and mealy.

	Figure 1. Greenhouse tomato infected with bacterial canker showing brown streak on stem and vascular discolouration.
	Figure 2.  Greenhouse tomato leaves with bacterial canker showing marginal leaf necrosis.
	Figure 3. Field tomato infected with bacterial canker showing wilting and death of lower leaves. Photo courtesy D. Cuppels, Agriculture & Agri-Food Canada

Fruit – Infected fruit may have yellowing or browning in its vascular tissue, may have a marbled appearance, or may be symptomless. A reported diagnostic feature of bacterial canker is the formation of fruit spots bordered by a distinct white halo on green fruit called “bird’s-eye” cankers (Figure 4). Although this symptom is helpful for visual identification, it is not likely to be observed in the early stages. DO NOT rely on this halo symptom to tell you if you have bacterial canker.

Figure 4.  "Bird's-eye" cankers on tomato fruit. Photo courtesy D. Cuppels, Agriculture & Agri-Food Canada

If you suspect you have the disease:

• Immediately send plants with symptoms for diagnosis to The BCMAL Plant Diagnostic Laboratory (1767 Angus Campbell Road, Abbotsford). Refer to the Plant Lab Webpage for submission forms, instructions and fees.

Once bacterial canker is confirmed:

Immediately:

• Remove infected plants and adjacent plants carefully.
• Place infected plants in plastic bags to reduce spread and remove from greenhouse.
• Do not reuse sawdust or bags from any infected plants.
• Disinfect pruning tools promptly.
• Wash hands well and change clothing after infected plants are removed (wash clothing before wearing them again).
• Limit the traffic in the areas where infected plants were found. Work with plants in the infected area last or assign certain workers to this area.
• Monitor the crop carefully for disease. Pay close attention to plants in the proximity of the initial outbreak.
• Applying a copper fungicide to the area of outbreak will help to reduce the disease, however preventative applications of copper-containing fungicides have not been effective in controlling the disease in field studies and are not recommended.

Prevention for the following growing season:

• Thoroughly clean the greenhouse after harvest. Remove plant material, clean all greenhouse surfaces, and disinfect irrigation lines. Refer to the BCMAL Factsheet “Greenhouse Vegetable Crop Clean-up” for details.
• Buy seed/transplants from a reputable source.
• Examine transplants before planting. Plant only healthy seedlings.
• Reduce possible sources of soil or moisture contamination.
• Install a foot bath with a disinfectant at the greenhouse entrance.
• Disinfect pruning equipment.

Ministry of Agriculture and Lands
Abbotsford Agriculture Centre
1767 Angus Campbell Road
Abbotsford BC V3G 2M3
Phone: (604) 556-3001
Fax: (604) 556-3030

July 2006

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