Tomato Bacterial Spot


On tomato, leaf lesions are initially circular and water-soaked and may be surrounded by a faint yellow halo. In general, spots are dark brown to black and circular on leaves and stems. Spots rarely develop to more than 3 mm in diameter. Lesions can coalesce causing a blighted appearance of leaves and a general yellowing may occur on leaves with multiple lesions. Infected pepper leaves drop prematurely; this exposes fruit to the sun and results in sun scalding. Fruit lesions begin as small, slightly raised blisters, which become dark brown, scab-like, and can appear slightly raised as they increase in size.

On leaflets, bacterial spot can be easily confused with the early symptoms of bacterial speck, early blight, gray leaf spot, target spot, or Septoria leaf spot. When Xanthomonas is present, bacteria will ooze (also referred to as bacterial streaming) from infected tissue and can be observed under a light microscope. Bacterial streaming will not be observed in lesions caused by fungal pathogens.

Bacteria survive on plant debris in the soil for one to two years, but will not survive once plant debris is broken down.
Introduction is primarily on infected seed or infected transplants. Even seedlings that do not show symptoms may be infected and will show symptoms later in the growing season.
Bacteria can spread from plant to plant by tools, workers’ hands, or through splashing rain or irrigation water.
Between rotations, the bacteria may survive on tomato or pepper volunteer plants.

Signs and symptoms

  • Tomato leaves have small (<1/8 inch), brown, circular spots surrounded by a yellow halo.
  • The center of the leaf spots often falls out resulting in small holes.
  • Pepper leaves have small (<1/8 inch), brown, circular spots that do not have a yellow halo and centers do not fall out.
  • Small, brown, circular spots may also occur on stems and the fruit calyx.
  • Fruit spots are ¼ inch, slightly raised, brown and scabby.
  • Tomato fruit often have a waxy white halo surrounding the fruit spot.
  • Pepper fruit spots often occur on the stem-end of the fruit.
  • Spots occur on green and red fruit but do not result in rot.

Management

  • The most effective management strategy is the use of pathogen-free certified seeds and disease-free transplants to prevent the introduction of the pathogen into greenhouses and field production areas. Inspect plants very carefully and reject infected transplants- including your own.
  • In the greenhouse, discard trays adjacent to outbreak location to minimize disease spread.
  • Treat seeds with dilute bleach, hydrochloric acid, or hot water to reduce the potential for seedling infection. However, this seed treatment is not recommended for producers that use pelleted seeds as it will remove the pelleted coating from seeds. These treatments may also reduce seed germination. Perform a test treatment on approximately 50 to 100 seeds and check for the effect on germination before treating an entire seed lot. 
  • In transplant production greenhouses, minimize overwatering and handling of seedlings when they are wet.
  • Trays, benches, tools, and greenhouse structures should be washed and sanitized between seedlings crops.
  • Crop rotation should be used to avoid pathogen carryover on volunteers and crop residue. Avoid fields that have been planted with peppers or tomatoes within one year, especially if they had bacterial spot previously.
  • Eliminate solanaceous weeds in and around tomato and pepper production areas.
  • Keep cull piles away from field operations.
  • Do not spray, tie, harvest, or handle wet plants as that can spread the disease.



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