There are several bacterial diseases of solanaceous crops. Three bacterial diseases, including bacterial canker (Clavibacter michiganensis subsp. michiganensis), bacterial spot (Xanthomonas campestris pv. vesicatoria), and bacterial speck (Pseudomonas syringe pv. tomato), are the most important, particularly on tomatoes, in Illinois.
Symptoms
Bacterial spot
The bacterium Xanthomonas campestris pv. vesicatoria, can seriously limit the yield of tomato and pepper crops. Distinct symptoms occur on pepper and tomato fruit, leaves, and seedlings and on pepper stems. Young leaves and fruit are more susceptible than older tissues. Pepper leaf lesions are usually dark green, water-soaked, not noticeably raised, and up to 1/8 or 1/4 inch in diameter. Later, these lesions develop dead, pale yellow centers with dark brown borders. Spotted leaves may turn yellow and fall at any time during the season. When lesions are numerous, entire leaves may drop off while still green. Fruit spots are blisterlike, roughly circular, and up to 1/4 inch in diameter, with a cracked, roughened, or wartlike appearance. Tomato leaf spots appear as small (1/8-inch-diameter), water-soaked, translucent lesions that later turn brownish black and may have a yellow halo. The lesions are somewhat irregular and appear greasy on the upper leaf surface, with a translucent center and a black margin. The centers of the lesions dry out and frequently tear. Only a few spots may cause a leaflet to turn yellow, wither, and drop prematurely. Spots on green fruit first appear as small, black, raised pimples surrounded by a narrow, water-soaked border. As they age, spots are slightly raised, superficial, and up to 1/3 inch in diameter, with lobed margins and water-soaked borders. Eventually the raised center sinks, forming a brownish black crater, which usually does not penetrate the seed cavity.
Bacterial speck
The bacterium Pseudomonas syringae pv. tomato causes foliar symptoms on tomato that are virtually identical to that of bacterial spot. Bacterial spot and speck can be differentiated by the symptoms they cause on immature fruit. Bacterial speck appears as black, slightly sunken stippling, which eventually results in lesions less than 1/16 inch in diameter. With both diseases, only immature fruit are infected.
Life Cycle
Both pathogens are introduced to production areas by contaminated seed and transplants and are spread by splashing rain and equipment moving through the field. Overhead irrigation; frequent, warm, driving rains; and long dew periods favor severe outbreaks of bacterial spot. The optimum temperature for infection is between 75 and 86 F. Bacterial speck is favored by similar but cooler conditions (65 to 75 F).
Management
Bacterial canker
Plant pathogen-free seeds and transplants. Seed-borne bacteria can be eradicated by seed treatment with acetic acid or hot water. Sterilized soil, potting mix, and pots or flats should be used in greenhouse operations. Clippers and pruning tools should be disinfested between plantings and rows, respectively. If stakes are to be reused, they should be steamed or washed with a 1% beach solution. After harvest, incorporate plant debris into soil to encourage the decomposition of debris. Crop rotation with a non-host is effective in reducing disease incidence.Applicaitons of effectvie bactericides are recommended.
Bacterial spot and bacterial speck
Once established in seedbeds and production fields, bacterial spot isdifficult to control. Plant certified, pathogen-free seed or transplants. Resistant varieties are available. Do not grow susceptible hosts in the same field more than once every two or three years and avoid excessive nitrogen fertilization. Limit the use of overhead irrigation and avoid cultivating, harvesting, or otherwise handling plants when they are wet. Where feasible, cleanly plow under or collect and burn crop debris immediately after harvest. Where bacterial spot or speck has been identified, apply a recommended bactericide after transplanting and continue until the first formed fruits are one-third their final size. Alternate or tank-mix with a suggested fungicide to improve control and maintain protection from other diseases.