Beginner

Scientific Name
Clavibacter michiganensis subsp. michiganensis

Identification

• Early (systemic) infections from infected seed or seedlings:
  • Most severe.
  • Cause the plant to wilt, often on only one side.
  • Streaking or open cankers may appear on the stems
  • A light reddish-brown discolouration may be seen in the vascular tissue, just above the soil line.
• Secondary infections:
  • More common, and less severe.
  • Show up later in the season.
  • Leaves develop brown-to-black margins with a thin, yellow border.
  • Leaflet edges usually curl upwards.
• Infected fruit may develop “bird’s-eye” spots- small lesions with light brown centres and a greasy white halo.

Often Confused With
Early Blight
Bacterial Spot

Period of Activity
The time for concern is from plant emergence through to harvest. Warm, wet weather conditions with temperatures of 24- 32°C (75- 90°F) favour the spread of this disease.

Scouting Notes
To confirm bacterial canker, choose representative plants showing early symptoms to send for diagnosis. Submit as much of the plant as is practical, or several plants showing a range of symptoms.

OMAFRA Publication 838, Vegetable Crop Protection Guide, provides information on pest diagnostic services in Ontario.

Thresholds
None established. Fruit lesions can reduce marketability, while defoliation can lead to poor colour development, poor holding or sunscald of fruit.

Advanced

Scientific Name
Clavibacter michiganensis subsp. michiganensis

Identification
Bacterial canker may occur in tomato as a primary (systemic) or secondary (foliar) infection and shows a wide range of symptoms.

Primary infections originate from infected seed or from invasion of the vascular tissue of young seedlings. Symptoms, which may not show up until several weeks after infection, initially appear as wilting and downward turning of the lower leaves. The wilting generally progresses upwards, unless the site of infection is in the upper part of the plant. Wilting is often seen only on one side of the leaf or one side of the plant. Plants may collapse and die, especially if infected at a very early stage. Generally, plants survive but are stunted, showing some or all of the symptoms described here, depending on their environment and stage of growth.

Tomato foliage infected with the canker organism has distinctive black leaf edges with no spotting on the interior of the leaves. Sometimes a thin yellow border is present between the dead leaf margins and healthy tissue.

If an infected stem is cut lengthwise, a light brown discolouration may be present in the vascular tissue, most noticeable at nodes and just above the soil line. As the disease progresses, this turns reddish-brown. Light coloured streaks are often visible on the outside of the stem. These may later darken and break open into cankers. With severe infections, a yellow ooze may exude from a cut stem when it is squeezed.

Fruit may develop relatively small spots with light brown centres, generally surrounded by a greasy white halo (3- 6 mm, 1/8- ¼ in. in diameter). These are known as bird’s-eye spots. With bacterial canker lesions, this white halo generally remains as the fruit ripens, while in the case of bacterial spot, it disappears with time. Bacterial canker may also cause a darkening of the vascular tissue in the fruit. The fruit may show a black peppering at the vascular bundles within the fruit, all the way to the seed. This can result in visible yellowish strands from the stem to the seeds and internal infections in the seed.

With a secondary foliar infection, leaves develop brown-black margins with a thin, yellow (chlorotic) band. Leaflet edges may curl upwards. Fruit may show bird’s-eye spotting, as in a systemic infection. Secondary infections (no vascular system involvement) often have minimal impact on the crop, especially when initiated later in the season.

Often Confused With
Early Blight (Look for the dark concentric rings that indicate early blight.  Early blight lesions enlarge and become angular over time.  No bird’s-eye spotting.)
Bacterial Spot (Bacterial canker and bacterial spot fruit lesions may develop as spots surrounded by a greasy white halo. With bacterial canker, this white halo generally remains as the fruit ripens; in the case of bacterial spot, it disappears with time.)

Biology
Infected seed is probably the major source for primary (systemic) infections. The bacteria can be present on the surface of the seed as well as within the innermost layer of the seed coat. This makes the canker organism harder to eradicate with seed treatments than the spot and speck pathogens.

The organism can also be introduced from infected crop debris, weeds hosts or volunteer tomatoes, and contaminated equipment. Infections spread through splashing water, wind-driven rain and the fine water droplets or aerosols producing during storms. In the field, bacteria transfer by machinery or workers is probably not as significant as in the transplant greenhouse where plant density is high and growth conditions for the bacteria are optimal.

The canker bacteria enter the plant through natural openings and wounds, including root wounds. Pruning or transplant clipping operations can introduce the bacteria directly into the vascular system, resulting in the more serious systemic infections.

Period of Activity
The time for concern is from plant emergence through to harvest. Warm, wet weather conditions with temperatures of 24- 32°C (75- 90°F) favour the spread of this disease.

Scouting Notes
Although bacterial spot and speck can cause lesions on leaf edges in some conditions, often dark brown to black leaf margins are an indication of bacterial canker.  Bacterial canker will not cause leaf spots like bacterial speck or spot, but can be found on the same plant with these diseases.

Early bacterial spot fruit lesions can appear whitish, resembling bacterial canker “bird’s-eye” spots, but only bacterial canker fruit lesions retain the whitish appearance.

To confirm bacterial canker, choose representative plants showing early symptoms to send for diagnosis. Submit as much of the plant as is practical, or several plants showing a range of symptoms.

OMAFRA Publication 838, Vegetable Crop Protection Guide, provides information on pest diagnostic services in Ontario.

Thresholds
None established. Fruit lesions can reduce marketability, while defoliation can lead to poor colour development, poor holding or sunscald of fruit.

Management Notes

• All tomato seed should be disinfected by the supplier, using acid or chlorine treatment.
• Do not plant diseased transplants.
• Keep transplants from different seed lots and different transplant growers separate to avoid cross-contamination. Keep tomato transplants separated from other host crops such as peppers. Areas of potential contact include in the transplant greenhouse, during shipping or holding plants, and in the field.
• Clean and sanitize plant trailer (any equipment used for shipping or holding) between loads.
• Clean and sanitize the transplanter (surfaces that contact plants and trays) between fields and varieties.
• Transplanting crew cleans and sanitizes their hands at every break or changes to new disposable gloves.
• Clean and sanitize equipment that touches the crop between blocks of plants or between fields.
• In processing and unstaked fresh market tomatoes, eliminate hoeing and inter-row cultivating beyond 3 or 4 weeks after transplanting.
• When working with staked plants (pruning, tying), clean and sanitize tools between each plant. Change gloves or clean and sanitize hands every row.
• Crop scouts and other visitors instructed to clean and sanitize hands or wear gloves prior to entering each field. Wearing plastic booties which are changed after each field will also limit the spread of soilborne pathogens from field to field.
• Copper fungicides may slow disease development. Visit ONvegetables.com for up-to-date, research-based spray program recommendations for tomato bacterial disease.
• Experience has shown that if a bacterial disease outbreak can be delayed until after the main fruit set, the crop will be minimally affected. Once the plant has reached a full canopy, a low level of bacterial disease on the foliage can be tolerated. Fruit lesions, which have a major impact on marketable yield, can only be initiated on young green fruit, so control measures used prior to fruiting are most beneficial.