Bacterial Ring Rot — Permaculture Database

Overview

Bacterial ring rot is a serious quarantine disease of potato caused by Clavibacter michiganensis subsp. sepedonicus. It is primarily seed-tuber transmitted and can devastate seed and commercial potato production. The bacterium survives in infected tubers, on contaminated equipment, and in storage. Very little inoculum can spread through a seed lot during cutting and handling. Because of its regulatory importance, suspected cases should be confirmed through official testing rather than assumed from symptoms alone.

Symptoms

Foliage may wilt, yellow, and roll upward, often starting with lower leaves. Vascular tissue in stems can show creamy discoloration. In tubers, a yellowish ring forms in the vascular ring; as the disease advances the ring softens and the tissue breaks down, sometimes with cheese-like ooze when tubers are squeezed. Mild infections may show little foliage symptom yet still contaminate seed. Symptoms can resemble other wilts and soft rots, so laboratory confirmation matters for seed lots.

Environmental Conditions

Variable

Prevention

Buy certified seed potatoes every year from reputable programs. Sanitize cutting knives frequently if you must cut seed; better yet, plant whole small seed when practical. Keep farm and garden equipment used on potatoes separate from other tools when possible after an outbreak. Eliminate volunteer potatoes. Never move suspect tubers into clean storage. Report unusual vascular ring symptoms to extension or seed certification staff in commercial settings.

Management

There is no field cure. Destroy infected lots according to local seed-potato regulations. Thoroughly clean and disinfect cutters, graders, storage walls, and containers before handling healthy seed. Do not save seed from suspect fields. Plant only certified seed from programs that test for ring rot. After a confirmed outbreak, follow official sanitation and rotation guidance before returning potato to the same equipment stream or storage.