How to Manage Pests

Pests in Gardens and Landscapes

Bacterial soft rot and blackleg—Erwinia carotovora var. carotovora and E. carotovora var. atroseptica

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


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.

Rotted tissue caused by bacterial soft rot
Rotted tissue caused by bacterial soft rot

Black stem caused by blackleg
Black stem caused by blackleg

Statewide IPM Program, Agriculture and Natural Resources, University of California
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