Cause The bacterium, Clavibacter michiganensis subsp. michiganensis, is carried in or on seed and survives in infected tomato debris, weed hosts, volunteer tomatoes, or on contaminated stakes or equipment. Handling seedlings and normal watering may spread the bacterium in seed flats. In the field, handling or pruning plants, using contaminated equipment, cultivation, and rain or irrigation water may spread the bacterium. Plants may be infected at any growth stage.
Symptoms Early in the disease, leaflets wilt (petioles remain turgid) and edges curl up or turn brown. Lower leaves turn down. It is common for leaflets on one side to wilt while those on the other side of the midrib appear normal. Later, affected leaves become brown, wither, and die. Open cankers may be evident on petioles and/or midribs. Stems may have longitudinal discolored streaks or cankers. Vascular tissue in the stem and petioles almost always is discolored yellowish to reddish brown. Discoloration is most pronounced at the junction of the stem and petiole. If the stem is broken, often the pith can be pulled out of it as a result of the vascular tissue deterioration. Fruit, when infected, have approximately 0.25-inch spots with raised brown centers and white halos. If plants are from infected seed, the entire plant may wilt and die or fail to set fruit. If transplants are infected at clipping, seedlings may not show symptoms until transplanted to the field.
Cultural control
- Use only pathogen-free seed and transplants.
- When producing transplants, use pathogen-free soil and flats. Sterilize flats with boiling water or steam, or disinfect with a 5-min. soak in a bleach solution (1part bleach to 3 parts water). Clean flats to remove all organic matter before treatment.
- Disinfect pruners between plants, or snap off suckers with fingers instead of pruning with a knife.
- Disinfect stakes, trellises, and wires.
- Plant in pathogen-free fields, or use a 4-year field rotation.
- Eradicate solanaceous weeds such as nightshades and volunteer tomatoes.
- Do not plant in fields receiving irrigation or drainage water from severely contaminated fields.
- Do not handle plants when they are wet.
Chemical control
- Seed treatment with sodium hypochlorite. Wrap seed in a cheesecloth bag and soak with agitation 40 min. in 1.05% sodium hypochlorite (1 part household bleach to 5 parts water). Spread out seed and allow to dry. Prepare fresh solution for each batch of seed.
- Agri-Mycin 17 at 200 ppm of streptomycin sulfate. Apply first at the first-true-leaf stage, then at least twice more at 4- to 5-day intervals. Note: Resistance to this product may develop quickly. 12-hr reentry.
- Badge SC (Group M1) at 0.75 to 1.8 pints/A and 0.5 to 1.5 Tbsp/1,000 sq ft in greenhouses on 3- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
- Firewall at 200 ppm beginning when seedlings are in 2-leaf stage and continue on 4- to 5-day intervals until transplanted in the field. 12-hr reentry.
Biological control
- Double Nickel LC at 0.5 to 4.5 pints/A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O