Tomato (Solanum lycopersicum)-Bacterial Spot

Cause Xanthomonas vesicatoria (formerly X. campestris pv. vesicatoria) is a bacterium that overwinters in plant refuse for up to 2 years and can be seedborne. The bacterium infects solanceous weeds such as black nightshade and ground cherry; some strains also infect pepper. Disease may be spread in the field or greenhouse by water (rain, irrigation), insects, equipment, and animals. Temperatures between 75°F and 86°F with a high relative humidity promote disease. Water in the form of dew, rain, or sprinkler irrigation is important for spread.

Symptoms Small, semi-circular areas, which have a water-soaked appearance first appear on leaves. Initial leaf spots enlarge, turn dark brown, and are commonly irregular in shape. Small blisters can develop on fruit, and will eventually take on a brown, scabby appearance. Leaf spots can grow together, turning much on the leaf brown. Stems and petioles may exhibit dark streaks. Defoliation, stunting, and reductions in yield result from severe infections.

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 (1 part 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 3-year field rotation.
  • Eradicate solanaceous weeds such as nightshades and volunteer tomatoes.
  • Do not handle plants or work fields when they are wet.
  • Incorporate infected crop residues to hasten decomposition.

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.
  • Actigard 50WG (Group PO1) at 0.33 to 0.75 oz/A beginning within one week of transplanting or emergence. Preharvest interval is 14 days. 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.
  • LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Gave fair control when used alone in studies by North Carolina State University. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
  • Previsto (Group M1) at 1 to 2 quarts/A on 5- to 10-day intervals. 48-hr reentry. O

Biological control

  • Double Nickel LC at 0.5 to 4.5 pints/A on 3- to 10-day intervals. Gave poor control when used alone in studies by North Carolina State University. Can be applied the day of harvest. 4-hr reentry. O
  • Serenade Opti at 14 to 20 oz/A on 2- to 7-day intervals. Applications can be made up to and the day of harvest. 4-hr reentry. O
  • Stargus at 2 to 4 quarts/A plus a nonionic surfactant on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O

References Koike, S.T., Gladders, P., and Paulus A.O. 2007. Vegetable Diseases: A Color Handbook. St. Paul. MN: APS Press.

Meadows, I.M., and Sharpe, S.R. 2018. Evaluation of conventional and organic pesticides for control of bacterial spot on fresh market tomatoes, 2017. Plant Disease Management Reports 12:V110.