Lincoln University Helps Growers Protect Sweet Potatoes After Harvest

Sweet potatoes spend months growing underground, but what happens after harvest determines how well they keep. To help growers protect their crop, Lincoln University of Missouri (LU) recently hosted a half-day workshop focused on postharvest diseases that develop after sweet potatoes leave the soil.

The event combined research presentations with discussion, giving growers an opportunity to learn how infection occurs and what practices help reduce losses during storage.

"Most of the pathogens that cause sweet potato postharvest diseases require a wound," said Waana Kaluwasha, Ph.D., LU assistant professor of plant pathology, who led the workshop.

Sweet potatoes can easily become cut or scraped as they are dug, broken at the ends when separated from the vine or bruised when tossed into buckets or containers. Because some damage is difficult to avoid, growers rely on curing, a process that involves keeping freshly harvested sweet potatoes in warm, humid conditions to allow wounds to heal and the skin to set before washing and storage.

Sweet potato plants grow in rows at LU's George Washington Carver Farm, where the workshop took place.

"Curing is typically done for four to 10 days," Kaluwasha said, adding that conditions should remain around 85 degrees Fahrenheit with at least 85% relative humidity.

Ye Su, Ph.D., LU associate professor in agribusiness, also shared results from a recently ended survey examining how growers harvest, cure and store sweet potatoes. While all eight respondents reported curing their sweet potatoes after harvest, more than half said they did not control temperature or humidity during curing and storage.

Recommended storage conditions after curing include temperatures between 55 and 60 degrees Fahrenheit with at least 85% relative humidity. Warmer conditions encourage sprouting and moisture loss, while colder temperatures may cause chilling injury and make sweet potatoes more vulnerable to disease.

Growers were encouraged to keep storage areas clean and well-ventilated. Sweet potatoes showing signs of decay should be removed because some pathogens produce spores that may spread to other damaged sweet potatoes.

Educational materials and an interactive plant disease activity were available to participants during the workshop.

Kaluwasha reviewed several diseases growers may encounter, including Fusarium rot, Rhizopus soft rot and bacterial soft rot. She explained that some infections begin in the field but do not cause visible symptoms until storage, while others develop after harvest when conditions favor infection.

The workshop also included LU research supported by a Missouri Department of Agriculture Specialty Block Grant examining how curing time affects disease development. The experiment showed the greatest disease development in sweet potatoes that were not cured. Infection generally decreased as curing time increased. Four days appeared sufficient for some varieties, while others benefited from seven to 10 days.

Participants shared questions and experiences from their own operations, discussing storage practices, pest problems and the different types of sweet potatoes they grow, including orange-fleshed Beauregard and white-fleshed varieties such as White Bonita and Murasaki.

Mary-Jane McCoy participates in a discussion during Lincoln University's postharvest disease workshop.

For Mary-Jane McCoy, Kaluwasha's research extended beyond the workshop and into her own operation. Kaluwasha previously visited McCoy's farm near Jefferson City to examine diseases affecting her sweet potatoes and collect samples.

"It's interesting how connections are made," McCoy said.

The two first connected after McCoy posted extra garlic scapes on Facebook Marketplace. That interaction eventually brought Kaluwasha to her farm, where McCoy grows hundreds of sweet potato plants.

At the workshop, McCoy said the discussion about curing stood out most.

"I learned how important it really is to cure sweet potatoes," McCoy said. "There's a big benefit to waiting seven to 10 days."

For more information, please contact Waana Kaluwasha at [email protected].

Photos by Lynne Holsapple.