Bacterial spot is caused by four species of Xanthomonas and occurs worldwide wherever tomatoes or peppers are grown. Bacterial spot causes leaf and fruit spots, which leads to defoliation, sun-scalded fruit, and yield loss. Due to diversity within the bacterial spot pathogens, the disease can occur at different temperatures and is a threat to tomato production worldwide. Disease development is favored by temperatures of 75 to 86 ℉ and high precipitation. In North Carolina, it is more prevalent in seasons with high precipitation and less prevalent during dry years.

Bacterial spot symptoms on field tomatoes caused by Xanthomonas perforans.

Inga Meadows

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Bacterial spot symptoms on field tomatoes caused by Xanthomonas perforans.

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Bacterial spot leaf lesions caused by Xanthomonas euvesicatoria on pepper seedlings.

NC State University Plant Disease and Insect Clinic

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Bacterial spot leaf lesions caused by Xanthomonas euvesicatoria on pepper seedlings.

NC State University Plant Disease and Insect Clinic

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The disease is caused by four species of Xanthomonas (X. euvesicatoria, X. gardneri, X. perforans, and X. vesicatoria). In North Carolina, X. perforans is the predominant species associated with bacterial spot on tomato and X. euvesicatoria is the predominant species associated with the disease on pepper. All four bacteria are strictly aerobic, gram-negative rods with a long whip-like flagellum (tail) that allows them to move in water, which allows them to invade wet plant tissue and cause infection.

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.

View this brief video to help you identify bacterial spot of tomato!

Bacterial spot on pepper leaf

Inga Meadows

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Bacterial spot on pepper leaf

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Water-soaked lesions of bacterial spot on pepper

Inga Meadows

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Water-soaked lesions of bacterial spot on pepper

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Bacterial spot leaf lesions caused by Xanthomonas perforans on greenhouse tomatoes.

Amanda Strayer-Scherer

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Bacterial spot leaf lesions caused by Xanthomonas perforans on greenhouse tomatoes.

Amanda Strayer-Scherer

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Bacterial spot leaf lesions caused by Xanthomonas perforans on greenhouse tomatoes.

Amanda Strayer-Scherer

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Bacterial spot leaf lesions caused by Xanthomonas perforans on greenhouse tomatoes.

Amanda Strayer-Scherer

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Bacterial spot on tomato leaf.

Inga Meadows

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Bacterial spot on tomato leaf.

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Fruit, petiole, and stem lesions of bacterial spot caused by Xanthomonas perforans.

Amanda Strayer-Scherer

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Fruit, petiole, and stem lesions of bacterial spot caused by Xanthomonas perforans.

Amanda Strayer-Scherer

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Fruit lesions of bacterial spot caused by Xanthomonas perforans.

Amanda Strayer-Scherer

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Fruit lesions of bacterial spot caused by Xanthomonas perforans.

Amanda Strayer-Scherer

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Bacterial spot on tomato fruit and petioles.

Inga Meadows

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Bacterial spot on tomato fruit and petioles.

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Bacterial spot leaf lesions caused by Xanthomonas euvesicatoria on pepper.

NC State University Plant Disease and Insect Clinic

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Bacterial spot leaf lesions caused by Xanthomonas euvesicatoria on pepper.

NC State University Plant Disease and Insect Clinic

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Bacteria oozing/streaming from diseased pepper tissue.

Inga Meadows

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Bacteria oozing/streaming from diseased pepper tissue.

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Infected plant tissue such as seeds, transplants, tomato and pepper volunteers, and crop debris are all potential sources of bacterial spot inoculum. In North Carolina, most disease outbreaks can be traced to contaminated seeds or diseased transplants. Disease development is favored by temperatures of 75 to 86℉, and high precipitation and humidity. The pathogens can invade the plant through natural openings (e.g. stomata and hydathodes) and wounds.

Bacteria can move within fields by wind-driven rain, irrigation droplets, aerosols, and the handling of wet plants. The longer the plants are wet, infection is more likely to occur. After initial infection, the disease can spread rapidly throughout an entire field or greenhouse. The bacterial spot pathogens can be recovered from non-symptomatic plants as early as one week at distances of up to 4 m from symptomatic plants. In the greenhouse, the disease can spread up to 2 m to neighboring plants from symptomatic plants within three weeks due to overhead irrigation.

Bacterial spot leaf lesions caused by Xanthomonas perforans on greenhouse tomatoes.

Amanda Strayer-Scherer

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Bacterial spot leaf lesions caused by Xanthomonas perforans on greenhouse tomatoes.

Amanda Strayer-Scherer

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Management of the disease focuses on preventive control measures throughout the season. Once a field becomes infested, bacterial spot is difficult to control, especially under conducive disease conditions. Therefore, preventative control measures are very important. Losses can be reduced by adopting the following management strategies:

• 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. For specific instructions and recommendations please consult the Southeastern US Vegetable Crop Handbook.
• 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 to a non-solanaceous crop 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.

Several fungicides are labeled for use on tomato and pepper to manage bacterial spot (Table 1). All products provide the best control if applied preventatively; there are no curative products for bacterial spot management. For the latest fungicide recommendations for southern blight of tomato and pepper, see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents—always read and follow fungicide labels.

Organic growers should follow the general disease management recommendations above in addition to the products listed below to obtain adequate control of bacterial spot. All products listed are OMRI-approved at the time of this publication. Always check the label for current restrictions.

Home owners should use the general disease management recommendations listed above. Some of the products listed above may be available for home owners to use.

• The NC State Plant Disease and Insect Clinic provides diagnostics and control recommendations
• The NC State Extension Plant Pathology Portal provides information on crop disease management
• The Southeastern US Vegetable Crop Handbook provides information on vegetable disease management

This disease factsheet was prepared by the Meadows Plant Pathology Lab.

Funding for updating this factsheet comes from the United States Department of Agriculture (USDA)-National Instiute of Food and Agriculture (NIFA) (2017-70006-27141).