Protect Potatoes from Ring Rot

By Scout Nelson

Cody Molnar, SDSU Extension Horticulture Plant Pathology Field Specialist, along with Connie Tande and Madalyn Shires, highlighted the risks of bacterial ring rot, one of the most damaging diseases affecting potatoes and seed potatoes. The disease is caused by Clavibacter michiganensis subsp. sepedonicus and mainly affects stored tubers, though it can also harm crops in the field.

A recent sample from Northern South Dakota showed black lines beneath the surface of stored potatoes. After diagnostic testing, the potatoes tested positive for bacterial ring rot. This case shows why quick identification and laboratory testing are important for potato growers.

The disease often starts with black or brown lines just below the potato skin. As infection grows, the lines become wider, and the tuber begins to rot from the inside. During storage, infected potatoes may spoil large batches of potatoes and reduce harvest value. In the field, infected plants may show wilting, yellow leaves, leaf rolling, and dieback. Some infected plants may not show clear symptoms.

Ring rot is difficult to identify because it can look like other potato problems. Similar issues include Potato Leafroll Virus, Potato Virus Y, Verticillium Wilt, Charcoal Rot, and freezing damage in stored potatoes. Proper testing helps growers choose the right management steps.

The disease spreads through infected potatoes and contaminated surfaces. Bacteria can survive on tools, containers, storage bins, and farm equipment. It may also remain on decaying plant material in the field. Because of this, sanitation is one of the best prevention methods.

There are no effective pesticides for bacterial ring rot and no known resistant potato varieties. Growers should use certified disease-free seed potatoes and never plant infected tubers. Tools and equipment should be cleaned with soap and water. Disinfectants such as bleach or alcohol may help remove remaining bacteria.

Fields with past infection should be rotated to non-solanaceous crops such as broccoli or squash for at least two years. Clean seed, crop rotation, sanitation, and early diagnosis remain the best ways to protect potato crops from bacterial ring rot.

Photo Credit: gettyimages-npantos