Hurricane Matthew dumped over 1 foot of rain in various locations across North Carolina (NC) within about a 24-hour period. This has resulted in significant numbers of saturated soils and flooding events that have affected some of the sweetpotato crop. Significant numbers of sweetpotato fields have been saturated with rain water for 2 to 3 days and will likely experience some rot. Research reports indicate that as much as 50% loss occurred during harvest and storage under temperature conditions similar to those experienced by growers in recent days in NC.

Areas most likely to be affected are fields near streams, rivers or bodies of water that have overflowed; fields with low spots; and fields that have soils that do not drain well. If flood waters, defined by the FDA, as the flowing or overflowing of a field with water outside of a grower’s control, invade a field, the sweetpotatoes are considered “adulterated” and should not be sold for human consumption. Flooding events can present a potentially hazardous public health risks due to exposure to sewage, chemicals, heavy metals, pathogenic microorganisms or other contaminants. Importantly, the flood-affected crops should be disposed of in a manner that does not further endanger adulteration of other crops not involved in flooded conditions. Finally, precautions should be taken with replanting of flooded fields; replant depends on conditions such as temperature, weather, and soil type. Fortunately, fields of sweetpotatoes encountering these conditions, in NC are in the minority.

For fields of sweetpotatoes that have been saturated by rain water for 2 days or more, we advise growers to wait and harvest the roots in those fields later next week. Temperatures are forecast to be in the 80s next week, and those roots that have been predisposed to rot due to saturated conditions should begin to rot, thus will not be carried to the storage facility. Focus in the more immediate days should be on harvesting fields that have good drainage or where rain water has not settled in the field for an extended period of time.

Regarding storage houses in which there is no electricity to cool the sweetpotatoes, we suggest cooling them by opening up doors and vents to allow some cooler air movement from the outside through the buildings. This should help to cool the rooms given that temperatures outside will fall to about 50 F or a little lower during the night.

As roots are harvested, cured and stored, they should be checked frequently for rots. Roots that are harvested from soils that have been rainfall saturated soils are more prone to break down or rot than roots not exposed to those conditions. Roots exposed to water saturated conditions should be marketed as quickly as possible to minimize loss due to rots that will likely occur if kept in storage for relatively long durations (i.e., three or more months).

There are varieties that are more tolerant to water stress than others. How Covington responds to extended periods of water saturation in comparison to other varieties has not been tested. We will all learn together how Covington roots respond to these conditions. Some good news for the industry and consumers is that about 50% of the crop was harvested prior to Hurricane Matthew and so there should be reasonable supply of high quality sweetpotatoes to meet market needs. We can prepare for the worst but have hope for the best!

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Addendum: Please be advised and note the following federal rule. The text above has been modified to reflect this federal rule. Reference: http://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/EmergencyResponse/ucm287808.htm

“If the edible portion of a crop is exposed to flood waters, it is considered adulterated under section 402(a)(4) (21 U.S.C. 342(a)(4)) of the Federal Food, Drug, and Cosmetic Act and should not enter human food channels. There is no practical method of reconditioning the edible portion of a crop that will provide a reasonable assurance of human food safety. Therefore, the FDA recommends that these crops be disposed of in a manner that ensures they are kept separate from crops that have not been flood damaged to avoid adulterating “clean” crops (Ref. 1, 2, 3).”

“FDA recommends not replanting in flooded fields if flood waters have not receded and the soil has not sufficiently dried. FDA recommends the following assessment for formerly flooded production ground:

• Assessing field history and crop selection.
• Determining the time interval between the flooding event, crop planting, and crop harvest.
• Determining the source of flood waters (e.g., drainage canal, river, or irrigation canal) and whether there are significant upstream potential contributors of human pathogens.
• Allowing soils to dry sufficiently and be reworked prior to subsequently planting crops on formerly flooded production ground.
• Sampling previously flooded soil for the presence of microorganisms of significant public health concern or appropriate indicator microorganisms. Note: Microbial soil sampling can provide valuable information regarding relative risks, but sampling by itself does not guarantee that all raw agricultural commodities grown within the formerly flooded production area are free of the presence of human pathogens.

The waiting period before growers can replant depends on conditions such as temperature, weather, and soil type. Currently, FDA has not completed studies to determine the length of waiting time that is generally considered safe for replanting. State, industry, and university extension specialists have recommended a 30-60 day waiting period and/or soil testing prior to replanting to (Ref. 12, 13, 14, 15). While this time period is generally considered sufficient for fecal contamination to decline, chemical contaminations, if present, may continue to remain in the flood-affected soil (Ref. 12).”

Prepared By
Jonathan R. Schultheis, Extension Specialist, North Carolina State University, Raleigh, NC 27695
Billy Little, Extension Agent, North Carolina Cooperative Extension Service, Wilson Co., Wilson, NC 27893
Brandon Parker, Extension Agent, North Carolina Cooperative Extension Service, Johnston Co, Smithfield, NC 27577
Allan Thornton, Area Specialized Agent, North Carolina State University, Clinton, NC 28328
Diane Ducharme, Extension Associate, North Carolina State University, Mills River, NC 28759