How to Manage Pests
UC Pest Management Guidelines
Pathogen: Pseudomonas syringae pv. tomato
(Reviewed 12/13, updated 12/13)
In this Guideline:
Bacterial speck appears as dark brown to black lesions of various sizes and shapes on leaves, fruit, and stems. Tissue adjacent to the lesions is initially yellow. Leaf lesions are frequently concentrated near margins, causing extensive marginal necrosis (tissue death). Lesions on immature fruit are slightly raised and small, varying in size from tiny flecks to 0.125 inch (3 mm) in diameter and cause raised black spots on mature fruit. Fruit lesions are superficial, seldom penetrating more than a few cells deep.
Comments on the Disease
The bacteria survive in soil, in debris from diseased plants, and on seeds. Infection is favored by cool, moist weather. The pathogen is spread by splashing rain or sprinkler irrigation. Disease progress is stopped during hot weather. In severe cases, infected plants are stunted, which may result in a delay in fruit maturity and yield reduction.
Cultural controls and copper spray generally provide adequate control of bacterial speck in early planting.
There are two races in California: Race 0 and Race 1. Many varieties are resistant against Race 0 but none currently possess resistance against Race 1, which is the predominant race throughout the state.
Organically Acceptable Methods
Cultural control and some copper formulations are acceptable for use on organically certified produce.
Monitoring and Treatment Decisions
Copper-containing bactericides provide partial disease control. Timing is critical. Apply before rainfall and repeat at 10- to 14-day intervals when cool and moist conditions prevail. Copper is strictly a protectant and must be applied before an infection period occurs. One or two treatments are usually enough to protect tomatoes during the most susceptible stages of growth. Spraying can stop when temperatures move into the 90°F range.
Resistance or partial resistance to copper is common. This is somewhat overcome by combining copper with mancozeb.
UC IPM Pest Management Guidelines: Tomato
R. M. Davis, Plant Pathology, UC Davis