Clavibacter michiganensis pv. michiganensis
Bacterial canker (Clavibacter michiganensis pv. michiganensis) is one of the most destructive tomato diseases in Massachusetts. It can also occur on pepper, but is only economically important on tomato. This disease occurs worldwide and although its occurrence is sporadic, it can cause devestating losses. Bacterial canker is especially severe on transplanted or direct-seeded tomatoes that have been clipped or pruned.
Initial symptoms are the result of primary, systemic infection and first affect the lower leaves causing leaf curling, wilting, chlorosis, and shriveling. Plants infected from seed may die, fail to set fruit, or show no symptoms. In advanced stages, the pathogen spreads throughout the plant and causes poor growth, wilt, and plant death. Foliage throughout the canopy wilts, yellows, turns brown, and collapses. Stems can split resulting in open breaks or cankers and stems break easily. Secondary infections occur from rain splash onto foliage, stems, and fruit. Spots occur on green fruit and are very characteristic: white to yellow spots, 3-4 mm with raised brown centers (“bird’s eye spots”). If infected plants are present, the movement of bacteria from one plant to another during normal watering, handling, and ventilating activities occurs readily.
Sources of inoculum for this disease include seed, infected plant debris, weed hosts, volunteer plants, and contaminated stakes. Bacteria survive in the field as long as there is any infected crop debris. They persist longer in debris on the surface than in buried debris. Secondary spread occurs through splashing water, contaminated tools, workers' hands, and pruning and clipping activities.
Cultural Controls & Prevention:
Prevention is cost-effective. All of these tactics focus on prevention -- ensuring that disease-free plants go out into a “clean” environment. Bacterial canker outbreaks in the field require regular sprays with a copper or copper/maneb mix, with limited success. Prevention strategies are both the least expensive and the most effective way to control bacterial canker.
- Start with certified, disease-free seed or treat seed with hot water, hydrochloric acid, calcium hypochlorite, or other recommended materials. The bacterial canker pathogen can be seed-borne, both on the surface of the seed and under the seed coat.
- Control bacterial populations that may be present on the leaf surface of transplants in the greenhouse. Young transplants may not display symptoms of bacterial diseases. Inspect and remove suspect transplants. Lower the water pressure in irrigation equipment to avoid damaging leaves. Avoid the practice of mowing transplants to regulate transplant height.
- Plant into a clean field. Promptly incorporate crop debris after harvest. Rotate to a non-host crop before returning to tomato and do not allow volunteer tomato or weed hosts to survive. Bacterial canker survives in the field as long as there is any infected crop debris. It lasts longer in debris on the surface than it does in buried debris. Plowing after harvest will help to speed up the decomposition.
- Avoid working in fields when bacterial diseases are present and the fields are wet.
- Rotate tomatoes (and related crops such as potato and eggplant) for 2-3 years to a different field. Setting clean transplants into a field where canker-infected tomato was grown the previous year will result in early infection with canker and reduced yields.
- New fields should, as much as is possible, be located at a distance from last year’s fields -- as far as possible given the choices available on your farm.
- Bacteria on the surface of transplants can be effectively controlled by sprays of copper hydroxide or streptomycin in the greenhouse. Kocide DF, Agri-Strep and Agri-mycin 17, and Dithane F-45 are labeled for greenhouse use on tomato.
- Using bactericide in the greenhouse means a lower volume of chemical is used compared to multiple copper sprays in the field. Check the label carefully for required REI and personal protective equipment.
Chemical Controls & Pesticides:
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.