Ring rot of potato identification & organic treatment
Clavibacter sepedonicus
How to identify ring rot of potato
A quarantine-significant potato bacterium that plugs the vascular ring inside the tuber with a cheesy, cream-colored rot, usually spread from infected seed potatoes rather than the field.
Symptoms
- Wilting and yellowing of leaflet margins that can resemble other wilts above ground
- Cutting a tuber near the stem end reveals a cheesy, cream-to-yellow rot following the vascular ring just under the skin
- Squeezing an infected tuber can push out a cheesy ooze from the ring
- Foliar symptoms are often mild or absent even with significant tuber infection
Host crops
Potato.
How it spreads
Spreads almost entirely through infected seed potatoes and contaminated cutting knives/equipment used during seed-piece cutting; does not spread readily through soil alone.
Favorable conditions
Symptoms can develop at any point in storage or the growing season once the bacterium is introduced via infected seed.
Progression
- Seed-borne introduction (Planting infected seed pieces) — Bacteria are already inside the seed tuber, often symptomless.
- Vascular colonization (During the growing season) — Ring rot develops inside daughter tubers.
- Storage rot (In storage) — Cheesy vascular rot becomes more visible and can invite secondary soft rot.
Organic treatment for ring rot of potato
- 1. Destroy infected seed lots and equipment · high effort
There is no in-season cure; remove and destroy any lot showing ring rot symptoms and thoroughly disinfect cutting equipment with a labeled disinfectant.
When: Immediately at diagnosis
- 2. Do not replant tubers from a symptomatic lot · low effort
Source certified seed potatoes for the next planting instead of saving tubers.
When: Next season planning
Prevention
- Always plant certified, disease-free seed potatoes; this is the single most effective prevention step.
- Disinfect seed-cutting knives frequently, ideally between every seed lot.
- Avoid storing symptomatic and healthy tubers together.
Easy to confuse with
Fusarium dry rot (dry, powdery, not cheesy vascular ring), Bacterial soft rot (whole-tuber mush, not confined to the vascular ring).