Carrot (Daucus carota)-Bacterial Soft Rot

Cause Erwinia carotovora subsp. carotovora (syn. = Pectobacterium carotovorum subsp. carotovorum), a bacterium that survives in decaying refuse. It enters the root principally through cultivation wounds, harvest bruises, freezing injury, and insect openings. After infection, high humidity is essential for progress of the disease. When soft rot occurs in the field, it usually follows a period of waterlogging in low areas following excessive rain or irrigation. Carrots, parsnips, potatoes, onions, crucifers, and celery are only a few of the many plants attacked.

Symptoms A soft decay of the fleshy root tissue takes on a watery or slimy consistency as the rot progresses. Rotted tissues keep their natural color until they completely decay. In the field, tops of rotted carrots turn yellow and wilt as roots break down.

Cultural control

  • For the earliest and latest seedings of carrots, avoid fields subject to a high water table during wet conditions.
  • Harvest carefully, particularly during warm weather.
  • When soil temperatures are high, carrots harvested for immediate sale should be washed and cooled promptly and rinsed with clean, chlorinated water before being placed in a refrigerated holding area.
  • Harvest crops intended for long-term storage after soil and air temperatures drop. Keep storage as close as possible to 30°F to 32°F and 85% to 90% relative humidity.
  • Thoroughly clean and disinfect bins between storage seasons.

Biological control

  • Double Nickel LC at 0.5 to 4.5 pints/A for soil application on 14- to 28-day intervals. Can be applied the day of harvest. 4-hr reentry. O

Reference Farrar, J.J., Nunez, J.J., and Davis, R.M. 2000. Influence of soil saturation and temperature on Erwinia chrysanthemi soft rot of carrot. Plant Disease 84:665-668.

Segall, R.H., and Dow, A.T. 1973. Effects of bacterial contamination and refrigerated storage on bacterial soft rots of carrots. Plant Disease Reporter 57:896-899.