For more information on symptoms, refer to ERWINIA under WILTS.

Bacterial soft rot after late blight  Bacterial soft rot


Unlike pink rot and leak, soft rot is caused be the bacteria Erwinia carotovora that also causes blackleg during the growing season. The soft rot bacteria can be carried on seed pieces, borne in soil, borne in water, carried on insect bodies and equipment. Weeds in the field especially those related to potatoes such as nightshades and buffalo bur can harbor the bacteria. Planting infected seed increases the potential of harvesting infected tubers. Soft rot usually enters through swollen, water-logged lenticels (pores) on tubers. Infected vines release bacteria to the soil and the bacteria can move to new tubers through soil water. Soft rot, however, can also enter tubers through the stem end and wounds.

Control Practices:

In storage, soft rot only spreads easily but must enter through wounds either caused mechanically or by fungi such as leak and pink rot. Wet tubers having free water on the surface are very prone to soft rot infection. Chlorinated water will help avoid the spread of soft rot but will not affect bacteria that have already entered tubers. There is little data to support the effectiveness of applying germicides through ventilation or humidifying systems. Infection is highest shortly after harvest and declines during storage. The bacteria can survive in debris in storage bins from season to season. Metalaxyl will not affect Erwinia carotovora.

Tips to Prevent Soft Rot

  • Do not plant infected seed.
  • Control weeds esp. nightshades and buffalo bur.
  • Avoid harvesting under wet conditions.
  • Harvest mature tubers with set skin.
  • Harvest when air and soil temperature is below 70oF.
  • Harvest when pulp temperature is below 50oF.
  • Avoid bruising.
  • Dry tubers quickly.
  • Remove vines, clods and soil adhered to tubers before piling.
  • Avoid leak and pink rot.
  • Sanitize storage facility.
  • Eliminate condensation during storage.
  • Keep well ventilated in storage.
  • Cure tubers for 2-3 weeks at 50-55oF with good air flow.
  • Do not wash tubers before storing.
  • Dry tubers quickly.
  • Monitor storage piles for wet spots.
  • If using flume system, use chlorinated water replacing it often.
  • Do not let tubers submerge more than 1-2 inches in flumes.
  • Dry tubers thoroughly before packing.
  • Pack tubers in ventilated bags, having air holes.