Bacterial soft rot: Erwinia chrysanthemi

Symptoms

• Roots are affected in the field, or more commonly in storage, by a soft rot that turns diseased tissue light brown and watery .
• Lesions on storage roots often have a dark brown margin. Some storage roots appear healthy from the outside but are decayed internally.
• Infected roots show black streaks in the vascular tissue and eventually undergo a soft, moist decay.
• Mother roots often decay in plant beds. In the field, brown to black, water-soaked lesions appear on stems and petioles. Eventually, the stem may become watery and collapse, causing the ends of vines to wilt.
• Usually, one or two vines may collapse, but occasionally the entire plant dies.

Dispersal:

• The bacterium invades the host through wounds. It survives in crop debris or in association with weeds.
• Sources of inoculum may include soil, infected mother plants, or contaminated wash water and harvesting equipment.
• The disease is favored by warm, humid weather.
• Symptoms may not be visible at temperatures below 80 degrees F but may appear rapidly at temperatures of 86 degrees F or higher.

Management

• Carefully handle sweet potatoes during all stages of production. This is the most important control method for bacterial soft rot.
• Select mother roots from fields free of the disease.
• Cull roots infected during storage.
• Use vines cut above the soil surface for transplanting.
• Use a handling system that does not involve immersion of sweet potatoes in water.