Bacterial Stem Rot, Bacterial Root Rot, Bacterial Soft Rot

Erwinia species

These bacterial diseases may affect potato, sweet potato, onions, brassicas, carrots, beans, corn, tomato and more. The first symptom on sweet potato (other plants may be similarly affected) is wilting of one or two branches, though this eventually spreads to the whole plant. There may also be spots on the lower stem, which quickly enlarge into sunken, water soaked lesions. If you cut open the stem there is often internal discoloration. Lesions may also appear on the root, but more often they are internal and look fine on the outside. This disease continues to develop after harvest and spoils the roots in storage.

The bacteria lives in soil and infected plant debris and can be spread on water, feet, tools or infected planting material. It enters the plant through wounds and it is most problematic in warm, wet weather, though it can also occur at other times. The most important control measure is to plant certified disease free plant material. Also avoid injuring plants, which can allow the bacteria into a plant (plant whole seed potatoes, rather than cutting them into pieces). Remove crop debris after harvest and rotate crops for 3 years. Remove infected plants as soon as possible, to prevent its spread. Raising the pH of the soil can also help.

Image: Howard F. Schwartz, Colorado State University, Bugwood.org