Harvesting and Storing Sweet Potatoes that have been subjected to Saturated Soil Conditions

What can happen to sweet potato roots following flooding events or prolonged saturated soil conditions?  Under saturated soil conditions, oxygen is excluded from the soil, creating an environment that favors the production of ethanol.  Basically the starch in the roots is converted to ethanol under these anaerobic conditions.  In an attempt to obtain oxygen, the lenticels on the root may proliferate, which unfortunately allows bacteria to enter and the roots will subsequently begin to sour or rot.  This process is not reversible and it is possible that obvious damage may not be apparent until after the roots are harvested.  One visible symptom to look for in the roots is a lack of the white latex or “milk” as it is commonly referred to, when the potato is sliced open.  

Damage to the roots (rot, souring or the beginning of decomposition) will be present to some extent in most production fields throughout the state.  Possible risk of damage will vary with soil type (light textured soils would be less risk) and drainage (better drainage = less risk). In general, if there is standing water in the middles after 2-3 days (with high air temperatures) of the last rain event, there is increased risk for damage in those areas. 

When harvesting sweet potatoes from saturated conditions it is paramount to grade as carefully as possible and minimize the amount of “bad or rotten” potatoes that you are placing in bins.  

In addition, minimize any impacts to the sweet potatoes, which can create new wound sites and invite post-harvest disease problems.  End rots may also increase with time during storage so consider reducing the amount of time flooded roots are kept in storage.  Proper curing can dramatically reduce the incidence of end rots developing later in storage, even for flooded roots.

Adequate ventilation is the most important variable to consider when placing the sweet potatoes in curing and storage facilities.  If the roots are brought into the sheds with excess mud on them, it is critical to get air moving around and through the bins to begin the drying process.   The curing process (increased heat and humidity) can increase the rate of decay on compromised roots that were harvested under adverse conditions.  It is possible that these roots may continue to breakdown during the curing process.  

You should move large amounts of air around and through the sweet potatoes and store them under ambient conditions with adequate ventilation.   Keep in mind that any mud around the potatoes will provide a lot of moisture “humidity” around the roots and as such, your humidity requirement during the curing process can be reduced to about 70%.  In addition, the temperature should be decreased to around 80-85 degrees with sufficient ventilation.  

Please contact the LSU AgCenter for any questions you may have about this information or any other crop related needs.

Myrl Sistrunk – 318-267-6712

Tara Smith – 318-557-9501

List of symptoms characteristic of roots exposed to saturated soils:

  • Circular spot may increase prior to harvest.

  • Lack of latex or milk when the roots are cut, any liquid exudates from the roots will be clear and not white.

  • Storage area may have a sour smell because of decomposing roots. The sour smell is a direct indication of soured and rotten roots that have been subjected to anaerobic conditions prior to storage. Under oxygen deprived conditions the starch in the roots is converted to ethanol.

  • Cut and intact roots may have a sour smell due to being harvested from an anaerobic environment.

  • Soft spots or lesions on the root may be visible, and/or the lenticels may appear raised and darkened.

  • The inside fleshy portion of the root will be lighter in color compared to sound roots.

  • Skin color may change from rosy to a tan hue, but many such roots may have no other problems.

  • Surface mold, often white or purple, may be visible on the root exterior and skin color of the roots may be darker and redder.

  • Presence of gnats and fruit flies in the storage facility.

  • Presence of post-harvest diseases such as Bacterial soft rot and Rhizopus soft rot in the roots.