Sweet potatoes are susceptible to a number of diseases, among these is bacterial soft rot of sweet potato. Sweet potato soft rot is caused by the bacterium Erwinia chrysanthemi. Rotting may occur either when growing in the garden or during storage. Also referred to as sweet potato bacterial stem and root rot, bacterial sweet potato rot is favored by high temperatures combined with high humidity. The following article contains information on identifying the symptoms of sweet potato soft rot and how to control the disease.
Symptoms of Sweet Potato Bacterial Stem and Root Rot
As the name suggests, the bacterium, E. chrysanthemi, results in rotting of both the tuber and root system of sweet potatoes. While rotting may occur during growing, the infection is more common in stored sweet potatoes.
In the garden, foliage symptoms appear as black, necrotic, water soaked lesions. Stems are also afflicted with dark brown to black lesions along with dark streaks apparent in the vascular tissue. As the disease progresses, the stem becomes watery and collapses which causes the tips of the vines to wilt. On occasion, the entire plant dies, but more commonly, one or two vines collapse.
Lesions or rotting in the root is more commonly found during storage. Roots afflicted with bacterial soft rot of sweet potato become light brown in color and watery accompanied by lesions with a characteristic dark brown margin. During storage, some roots may appear untouched by the disease until they are cut into wherein decay becomes evident. The infected roots are streaked with black and become soft, moist and rotten.
Bacterial Sweet Potato Rot Control
Sweet potato rot is introduced through wounds, so minimizing wounding of the roots will help to curtail the incidence of the disease. Handle the sweet potatoes carefully as they are being harvested and stored, and work around them gently when weeding or the like. Wounding may be caused by mechanical means but also by insect feeding, so controlling insects will also help to control the spread of the disease.
Also, some varieties of sweet potato are more susceptible to the disease. For example, ‘Beauregard’ is very susceptible to root rot. Use cultivars with a tolerance to bacterial sweet potato rot and select only certified disease-free propagating materials. For transplanting, only use vines that have been cut above the soil’s surface.
Lastly, immediately remove and destroy any infected roots found during storage to prevent the spread of sweet potato rot.