Symptoms of soft rot include rotted tissues that are wet, cream to tan in color, and soft. Rot begins on the tuber surface and progresses inward. Infected tissues are sharply delineated from healthy tissue by dark brown or black margins. Shallow necrotic spots on the tubers result from infections. Rotting tissue is usually odorless in the early stages of decay, but develops a foul odor as secondary organisms invade infected tissue. Plants with blackleg are stunted and have a stiff, erect growth habit. Foliage becomes chlorotic and the leaflets tend to roll upward at the margins. Stems of infected plants exhibit an inky black decay. The base of the stem is often completely rotted. In relatively dry soil, only the pith may show blackening. Tuber symptoms for blackleg are similar to those of soft rot.
Life cycle
Bacterial soft rot and blackleg infections are favored by high soil moisture and high temperatures. The bacteria are carried in and on seed pieces, in soil, and in water. It can also be spread by insects and enter growth cracks or any injury. During and after harvest, soft rot is favored by immature tubers, adverse temperatures, mechanical damage, and free water on tuber surfaces.
Solutions
Avoid planting in extremely wet soil, provide good drainage, and do not overirrigate. Use high quality, pathogen-free tubers for seed and avoid excessive hilling when planting. Avoid excessive soil moisture before harvest to reduce infection; harvest mature tubers with well-set skins and avoid mechanical injury. Use clean water to wash potatoes and avoid water films on tuber surfaces during storage. Eliminate cull piles and potato volunteers in rotation crops. Avoid susceptible varieties.
