Xanthomonas Bacterial Spot
Bacterial spot caused by Xanthomonas campestris pv. vesicatora (Xcv) is present wherever tomato and peppers are grown. In general, Xanthomonas pathovars have narrow host ranges. Xcv consists of different strains that vary in their pathogenicity to tomato, pepper, and nightshade. Xanthomonad pathogens from tomato and pepper hosts are complex. At least three strains specific for tomato have been described. Other strains are specific to pepper and still others are pathogenic to both pepper and tomato. Pepper cultivars are available with resistance to bacterial spot, however they are usually resistant to specific races (strains) of Xcv. Effective control of Xcv with resistant varieties requires knowing what races of the pathogen are likely to be present.
Xcv affects all aboveground plant parts. On leaves, the spots are generally brown, circular, and watersoaked. Bacterial spot lesions do not have concentric zones or a prominent halo. Fruit lesions are balck and may be scablike or sunken. When conditions are optimal for disease development, spots can coalesce to form long, dark streaks. A general yellowing may appear on foliage with many lesions giving the plants a scorched appearance, and the plants may exhibit severe epinasty.
Xcv is seed-borne and as a little as 0.01 % of infected seed can result in an epidemic. Disease development is favored by temperatures between 80° and 90° F and by heavy rainfall. The bacterium is spread by wind-driven rain, workers, farm machinery, and aerosols. It penetrates through stomates and wounds created by insects, wind-blown sand, and tools.
- Buy certified seed from a reputable source or use seed treatments to reduce transmission.
- Sanitation and environmental manipulation are important disease management principles.
- Produce disease free transplants by raising transplants in an area where production does not occur.
- Inspect all purchased transplants carefully and if transplants originate in southern states they should be certified.
- Rotate fields to avoid carryover on volunteers or crop residue. Use at least a one year rotation to crops that are not hosts.
- Keep fields free from volunteers, weeds, and cull piles.
- Avoid working in fields when bacterial diseases are present and the fields are wet.
- In general, bacterial diseases of field crops are difficult to control with pesticides. When a significant amount of disease is present, pesticides are usually not effective.
For Current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the New England Vegetable Management Guide website.
Diseases
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