Xanthomonas Bacterial Spot
Bacterial leaf spot caused by Xanthomonas campestris pv. vesicatora (Xcv) is the most common and most destructive disease of peppers in the Northeast. This disease is present wherever tomato and peppers are grown. There have been six races (pathovars) identified to date. 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 of Xcv. Effective control of Xcv with resistant varieties requires knowing what races of the pathogen are likely to be present.
Bacterial spot lesions do not have concentric zones or a prominent halo. On leaves, the spots are generally brown, circular, and watersoaked. 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 affects all aboveground plant parts and fruit may become heavily infected.
Seed is an important mechanism for survival and dissemination of Xcv. One infested seed in 10,000 may easily result in 100% diseased plants in the field under proper conditions. 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.
Complete crop failure has occurred due to this disease. Marketable yield is reduced both by defoliation and damaged fruit. Defoliation reduces crop productivity and also exposes the fruit to sunscald. Fruit lesions can provide entry points for soft-rotting organisms.
- Buy certified seed from a reputable source or use seed treatments to reduce transmission.
- 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.
- Sanitation and environmental manipulation are important disease management principles.
- Apply appropriate bactericides or combination pesticides. In general, bacterial diseases of field crops are difficult to control with pesticides; copper/mancozeb solutions are most effective.
- 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
Get real-time updates from the field on emerging pests, upcoming meetings, and extension projects on our Facebook page!
