Bacterial Canker — Permaculture Database

Overview

Bacterial canker of tomato and related crops is caused primarily by Clavibacter michiganensis subsp. michiganensis. It is a systemic vascular disease that can devastate greenhouse and field tomato crops. The bacterium spreads on seed, transplants, tools, and splashing water. It survives in plant debris and can infect through wounds from pruning, staking, or insect feeding. Once in the vascular system, it moves systemically and is difficult to eradicate from a planting.

Symptoms

Early signs include wilting of leaflets on one side of a leaf or plant, yellowing, and marginal leaf burn. Stems may show light brown vascular discoloration when split open. Fruit can develop raised white spots with dark centers (bird's-eye spots). Open cankers on stems and petioles ooze under humid conditions. Seedlings may collapse; older plants decline slowly with progressive wilt. Symptoms can resemble other wilts, so vascular streaking and bird's-eye fruit spots help distinguish canker.

Environmental Conditions

Cool

Prevention

Plant only certified disease-free seed and transplants. Hot-water or approved seed treatments reduce seedborne inoculum when done carefully. Practice strict tool sanitation during pruning and suckering. Space plants for good airflow and water at the soil line to limit splash. Remove nightshade weeds that can harbor the bacterium. Rotate solanaceous crops and avoid returning tomato to the same greenhouse bay without sanitation after a canker year.

Management

Roguing infected plants immediately and bag them for disposal rather than composting. Disinfect pruning tools between plants. Avoid working tomatoes when foliage is wet. Copper sprays offer limited suppression of surface spread but will not cure systemic infection. In greenhouses, remove heavily contaminated media and sanitize benches, stakes, and clips. After an outbreak, rotate out of tomato and related solanaceous crops and thoroughly clean up debris before the next cycle.