Bacterial canker identification & organic treatment
Clavibacter michiganensis subsp. michiganensis
How to identify bacterial canker
A systemic tomato bacterium that moves inside the plant's vascular system, causing one-sided wilting, stem cankers, and a telltale 'bird's-eye' spot on fruit.
Symptoms
- Wilting and curling of leaflet margins, often starting on one side of the plant
- Leaves turn brown and dry but tend to stay attached to the stem
- Streaked, cracked cankers on stems that ooze bacterial slime when cut
- Small, flat white-centered spots with a dark ring ('bird's-eye spot') on fruit
Host crops
Tomato.
How it spreads
Seedborne, moves within a plant through the vascular system, and spreads plant-to-plant via pruning tools, contaminated stakes, and splashing water.
Favorable conditions
Warm, humid weather favors spread; the bacterium survives in dry plant debris for a year or more.
Progression
- Systemic infection (From infected seed/transplant) — No visible symptoms initially; bacteria move through the vascular system.
- One-sided wilt (Fruiting stage) — Leaflets curl and brown on one side of a stem or plant.
- Canker and fruit spotting (As disease advances) — Stem cankers form; fruit shows bird's-eye spotting.
Organic treatment for bacterial canker
- 1. Remove and destroy infected plants · high effort
Pull whole plants showing one-sided wilt or cankers; do not compost, and disinfect tools used on them.
When: Immediately at diagnosis
- 2. Sanitize tools and stakes between plants · low effort
Dip pruning shears in a 10% bleach or alcohol solution between every plant when canker is suspected in a planting.
When: Ongoing once seen
Prevention
- Use certified pathogen-free seed; this disease travels almost entirely on seed and transplants.
- Rotate out of tomato ground for at least 3 years after an outbreak.
- Avoid handling wet plants, especially when pruning or staking.
- Discard, don't compost, cankered debris.
Easy to confuse with
Fusarium/verticillium wilt (no bird's-eye fruit spot, no bacterial ooze), Bacterial spot (spots only, no systemic wilt).