Beginner

Scientific Name
Xanthomonas campestris pv. vesicatoria

Identification

• May produce lesions on all above-ground parts of the plant - leaves, stems, flowers, and fruit
• Only green fruit is susceptible to infection, not red fruit
• Infected fruit develop small, raised, dark spots
• Young fruit lesions may have a white halo, similar to bacterial canker
• Spots increase in size to 3- 5 mm (1/8 - 3/16 in.) in diameter and develop brown corky centres
• Severe infections may cause defoliation

Often Confused With
Bacterial Speck
Bacterial Canker

Period of Activity
Bacterial spot prefers warm temperatures of 24- 30°C (75- 86°F). Abundant rainfall and high humidity aid infection.

Scouting Notes
It is difficult to distinguish bacterial speck and bacterial spot by symptoms on the foliage.  Fruit symptoms are generally diagnostic, based on lesion size and appearance.

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 on foliage 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 spot 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. Tolerance is low in fresh-market or processing tomatoes (wholepack and diced) due to marketability and peeling issues.

Advanced

Scientific Name
Xanthomonas campestris pv. vesicatoria

Identification
The bacterial spot pathogen may produce lesions on all aboveground parts of the plant- leaves, stems, flowers and fruit. It is difficult to reliably distinguish bacterial spot from bacterial speck based on visual symptoms, especially in the early stages.

Initial leaf symptoms are small, circular-to-irregular, dark lesions, which may be surrounded by a yellow halo. The lesions tend to concentrate on the leaf edges and tips and may increase in size to a diameter of 3- 5 mm (1/8- 3/16 in.). Infected leaves may develop a scorched appearance. When spots are numerous, foliage turns yellow and eventually dies, leading to defoliation of the lower portion of the plant.

Lesions on pedicels may cause flower abortion, resulting in lost yield and split sets of fruit.

Fruit lesions are initiated only on green fruit, most likely because infection occurs through fruit hairs, which are present only on immature fruit. On fruit, the first symptoms are small, dark brown-to-black, raised spots. The lesions also may have a white halo, similar to bird’s-eye spotting seen with bacterial canker. As the fruit ages, the white halos disappear. Bacterial spot lesions may increase in size to 4- 6 mm (1/8 - 1/4 in.) in diameter and become brown, greasy-looking and sometimes scabby.

Often Confused With
Bacterial Speck
Bacterial Canker (Bacterial spot fruit lesions may also have a white halo, similar to bird’s-eye spotting seen with bacterial canker. As the fruit ages, the white halos disappear. In contrast, bacterial canker fruit lesions retain the white halo.)

Biology
The major sources of infection for these bacteria are thought to be seed and infected crop debris. They may also be present on volunteer tomato plants and on contaminated equipment and surfaces (farm machinery, racks, greenhouse structures, tools). The bacteria are spread primarily by splashing water and wind-driven rain or mists produced during storms. In the field, spread by equipment or workers is probably of lesser importance than it is in the greenhouse, unless wounds are being opened up at the same time, as in pruning operation or when plants are injured by a cultivator.

Bacteria enter the plant through natural openings (stomates and hydathodes) or wounds caused by wind-driven soil, insects or mechanical damage (handling, wind whipping, high pressure sprayers).

Period of Activity
Bacterial spot prefers warm temperatures of 24- 30°C (75- 86°F). Abundant rainfall and high humidity aid infection. The time for concern is from transplanting through to early flowering and fruit set.

Scouting Notes
It is difficult to distinguish bacterial speck and bacterial spot by symptoms on the foliage.  Fruit symptoms are generally diagnostic, based on lesion size and appearance.

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 spot 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. Tolerance is low in fresh-market or processing tomatoes (wholepack and diced) due to marketability and peeling issues.

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 alone have not shown efficacy against bacterial spot in recent trials. Visit ONvegetables.com for the most 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.