Can you help with controlling mold on our sweet potatoes?


I'm a sweetpotato grower and exporter based on the East Coast in the U.S.  Some of our sweets were rejected during international shipment due to Rhizopus soft rot which was confirmed by lab analyses.  I would like to ask for some help on controlling mold growing in our sweet potatoes. (J.C.)


This is, unfortunately, a recurring problem in sweetpotatoes and the solution revolves around sanitation of the dump tank.  The sweetpotatoes are usually dumped from bins into a water dump tank which is changed once a day and contains no chlorine disinfectant.  The microbial load builds up during the day and serves as a source of contamination.  The reason for not using chlorine is that with all the soil in the dump tank it is ineffective.  The dump tank is often followed by a high pressure wash of clean water.  Because of the physical handling on the packing line, the sweetpotatoes are being damaged and this damage is visible.  The key to this situation is improved sanitation at the dump tank.  A pre-dump wash will remove the sand adhering to the sweetpotatoes and allow less contamination in the dump tank.  Then the dump tank needs some disinfectant to minimize contamination, and two summaries about chlorine use provide practical guidelines.  In addition to this, the sweetpotato operation could also follow recommendations to cure the sweetpotatoes after packing. This would be a good addition to the handing practices for export in particular. Curing is the process to heal surface wounds caused by handling and is a key operation after harvest and before storage of sweetpotatoes.  It can also be beneficial to heal damage from the packingline.  The recommendations are 85/85 or 85°F (29°C) and 85% or higher relative humidity for a few days.  This step would also allow an additional quality check before the sweetpotatoes are loaded into containers for export.  For marine container shipment at 58°F (14-15°C), container loading is key to ensure proper airflow through the boxes.  If open floor areas in the rear of the container are not blocked, cool air will not flow up through the boxes and will allow buildup of humidity which also favors mold growth.

The focus on washing bins to remove sand before dumping, improving the dump tank sanitation, and holding the sweetpotatoes to recure them should all contribute to better arrival condition for your international shipments.

– Marita Cantwell