How to Manage Pests

UC Pest Management Guidelines

Pale, watersoaked leaf tissue surrounding brown lesions on pepper leaves caused by Xanthomonas campestris p.v. vesicatoria, eventually turn brown.


Bacterial Spot

Scientific name: Xanthomonas campestris pv. vesicatoria

(Reviewed 12/09, updated 12/09)

In this Guideline:


Bacterial spot appears as spots that form on leaves, stems, and fruit. Leaf spots first appear as small, angular spots on the undersurface of the leaf. The spots, which are about 0.25 inch in diameter, are initially water-soaked and later turn brown. Elongated raised cankers form on the stems. Fruit spots are circular, brown, and raised with a cracked, roughened, and wartlike surface.


The bacterium is seedborne and can occur within the seed or on the seed surface. The pathogen is disseminated with seed or on transplants. Bacterial spot is a relatively minor disease that is favored by high relative humidity and free moisture on the surface of the plant. Symptoms develop 5 to 15 days after inoculation and develop most rapidly at temperatures of 68°F or above. The bacteria do not survive in soil after the infected plant residue decomposes. Some strains of the bacteria favor pepper, others favor tomato, and others are equally pathogenic on both tomato and pepper.


Use indexed pathogen-negative seed, treated seed, or disease-free transplants. Rotate out of peppers for at least 1 year. Use furrow or drip irrigation instead of overhead irrigation. Treatment with copper spray is justified only under high pressure as might occur with sprinkler irrigations. Resistance to copper is known to occur in California populations of this pathogen.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460


S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis
K. V. Subbarao, USDA Research Station, Salinas

Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis

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