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Ministry of Agriculture, Food and Rural Affairs

Bacterial Speck

Bacterial speck symptoms on fruit and foliage Bacterial speck fruit lesion – scraped off with fingernail Bacterial speck fruit lesion Bacterial speck symptoms on foliage Bacterial Speck or Spot on Tomato Foliage Bacterial Speck or Spot on Tomato Stem, Sepals, Pedicels Bacterial Speck or Spot on Tomato Foliage
Click to enlarge.

Beginner

Scientific Name
Pseudomonas syringae pv. tomato

Identification

  • Bacterial speck lesions may occur anywhere on the foliage, stems, or fruit.
  • Only green fruit is susceptible to infection, not red fruit.
  • Fruit lesions are small (< 2 mm, 1/12 in. in diameter), black, slightly raised and often surrounded by a narrow green-to-yellow halo
  • Speck lesions on the fruit are usually superficial and can be scraped off
  • Severe infections may cause defoliation

Often Confused With
Bacterial Spot
Young Early Blight

Period of Activity
Bacterial speck favours cooler weather – 18- 24°C (64- 75°F). Abundant rainfall and high humidity aid infection.

Scouting Notes
To confirm bacterial speck 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 for plant disease diagnosis.

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
Pseudomonas syringae pv. tomato

Identification
Bacterial speck lesions may occur anywhere on the foliage, stems or fruit. On leaves, symptoms appear as black specks, usually no more than 2 mm (1/12 in.) in diameter), which are usually surrounded by a yellow halo. Speck lesions sometimes cause distortion of the leaf, as the infection restricts the expansion of leaf tissue. Lesions are often concentrated near leaf edges, and in some cases, leaf margin burn resembling bacterial canker may occur. When numerous, lesions may coalesce, and entire leaflets may die. Severely infected seedlings may become stunted.

Only green fruit less than 3 cm (1 1/5 in.) in diameter is susceptible to infection by the bacterial speck pathogen. Small (less than 1- 3 mm, 1/25- 1/8 in.), slightly raised black specks develop and are often surrounded by a narrow green to yellow halo. Lesions are usually superficial and can be scraped off with a fingernail. Red fruit are not susceptible to infection, likely due to a lack of entry points for bacteria; fruit hairs, which may break and allow bacteria to enter, are only present on young fruit. On fruit previously infected, black lesions remain after ripening.

Often Confused With
Bacterial Spot
Young Early Blight

Biology
Two races of Pseudomonas syringae pv. tomato are present in Ontario, race 0 and race 1. These bacteria produce a number of compounds that help them infect and obtain nutrients from the tomato plant. One of these compounds is the plant-specific toxin coronatine, which is responsible for the yellow halo surrounding leaf lesions and the stunting of young seedlings.

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 or 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 speck favours cooler weather – 18- 24°C (64- 75°F). Abundant rainfall and high humidity aid infection. The organism is inhibited when average daily temperatures exceed 21°C (70°F).

Scouting Notes
To confirm bacterial speck 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.
  • 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.