Ring rot

Ring rot (C. michiganensis ssp. sepedonicus) is a quarantine disease, which causes tuber rotting of potatoes. It is found in parts of North America and is also established in northern and eastern Europe.

Symptoms
Tuber symptoms can been seen when tubers are cut across the heel end (where the tuber was attached to the stolon). In the early stages the tissues around the vascular ring appear glassy and water soaked. As infection progresses the vascular ring becomes discoloured and a soft cheeselike rot develops around the vascular ring (hence the name “ring” rot). If a cut tuber is squeezed a cheese-like ooze emerges. External symptoms are not common but in severe cases the skin of the potato may crack and ooze can emerge from the heel end and eyes, causing soil to adhere.

Wilting symptoms may occur late in the season and are often masked by the natural senescence of the crop. Symptom expression occurs at different rates in different varieties and is affected by temperature and other environmental conditions. Some varieties hardly ever express symptoms.

Prevention
Plant only certified seed potatoes. Avoid using table stock for seed or importing seed from other areas for planting. Disinfect knives frequently while cutting seed pieces, to avoid spreading any disease that might be present but unnoticed. Bury cull piles and control volunteer potatoes. Clean and disinfect storage bins between crops and pressure-wash equipment to avoid spreading ring rot or other diseases.