Bacterial canker of tomato

Pathogen

The bacteria Clavibacter michiganensis subspecies michiganensis.

Identification

Signs and symptoms

Symptoms vary with age of plant, type of infection, environment and other factors. This disease can be difficult to diagnose based on symptoms alone. Confirm diagnosis by sending a plant sample to the UMN Plant Disease Clinic.

Seedlings

• Small, white, raised spots may form on leaves
• Seedling completely wilts and dies

Leaves

• Yellow to tan patches form between veins
• Edges of leaf turn brown, with a yellow border
• Dark, sunken veins on leaves and petioles
• Wilt on lower leaves, often on one side only
• Entire plant may collapse and die

Stem

• Brown streaks can be seen in the vascular system when the stem is cut open
• Stem splits forming long, brown cankers
• Yellow sticky fluid may emerge from cut stem when squeezed

Fruit

• Small (1/4 inch), creamy, white spots with tan or brown centers on fruit (bird eye spot)
• Fruit surface may appear netted or marbled

Environment

• Warm temperatures (75 to 90°F)
• High moisture or relative humidity

Biology and disease cycle

The bacterial canker pathogen is spread long distances and introduced to new areas through infected seed or transplants. The disease easily spreads between seedlings in a transplant production greenhouse through workers' hands, equipment, and pruning and clipping of transplants, so one infected seed can potentially result in many infected transplants, through which the disease can become established in high tunnels or fields. Transplants may be infected yet not initially show symptoms. In the field, infected transplants often die and secondary spread is limited or of little economic impact. However, in tunnels or greenhouses, the disease easily spreads between transplants and between older plants through practices like pruning and staking and can result in severe symptoms and yield loss. The pathogen survives up to three years on non-decomposed tomato plant debris and can survive for several months on stakes and equipment, thereby readily infecting tomatoes planted in the same tunnel the following season.

Management

Resistant varieties

There are currently no tomato varieties with resistance to bacterial canker.

Cultural control

• Plant certified pathogen-free seed from a reputable supplier.
• Do not save seed from infected plants.
• Treat any saved seed prior to planting.
  • Soak seeds in a solution of 1 part germicidal bleach to 4 parts water for 1 minute. Rinse in water for 5 minutes OR soak seed in 122°F water for 25 minutes.
  • Neither method will completely eliminate the pathogen, so the seedling should be carefully monitored for symptoms.
• Purchase healthy transplants from a reputable grower. Avoid transplants that have been pruned or cut back as this procedure easily spreads the bacterial pathogen.
• Disinfest tools and equipment between seasons with a commercial greenhouse sanitizer according to label instructions or by soaking in a solution of 1 part germicidal bleach to 9 parts water for 1 to 5 minutes.
• Discard strings and wooden stakes. These materials cannot be cleaned because they are naturally porous, making it difficult for the sanitizer to reach the bacteria inside.
• Avoid working in fields when the foliage is wet with rain, irrigation, or dew.
• Use a commercial greenhouse sanitizer or a 1:9 solution of bleach to water, to regularly clean pruning tools. To be efficient when pruning, have two pruners and alternate between them between plants to allow proper soaking time.
• In greenhouse or high tunnel production, promptly bag and remove infected plants, including roots to prevent spread.
• Remove and/or plow in remaining plant debris immediately after harvest to encourage decomposition.
• Infected plant debris can be composted on site. The pathogen will be killed if the compost heats up and all plant parts are completely broken down.
• Rotate away from tomato and related crops for two to three years.
• Control weeds in the solanaceae family, like nightshades, as well as volunteer tomatoes or peppers during the rotation.

Chemical control

There are very few chemical options for managing bacterial canker. Visit the Midwestern Vegetable Production Guide for a current list of treatment options.