Food Safety Considerations for Flooded Fields

Recent heavy rains across much of the state have resulted in widespread ponding and flooding in fields. This creates multiple considerations for those growing produce for fresh consumption.  Flooding and pooling create food safety challenges because of their potential to introduce contaminants (i.e. risk) into the production system. However, with proper management, many of these risks can be mitigated.

Figure 1. Flooding in a field.Flooding, defined as the “Flowing or overflowing of a field with water outside a grower’s control” is illustrated in Figure 1. Note that the Wabash River is visible through the break in the trees..

Figure 1. Flooding in a field. Flooding, defined as the “Flowing or overflowing of a field with water outside a grower’s control” is illustrated in Figure 1. Note that the Wabash River is visible through the break in the trees.

Figure 2. Pooling of water.Pooling is the collection of water in a low area of the field as is shown in a low corner of this asparagus planting.

Figure 2. Pooling of water. Pooling is the collection of water in a low area of the field as is shown in a low corner of this asparagus planting.

Following heavy rains, growers should first determine if water in their fields is the result of pooling or flooding. Pooling is more common than flooding.  Pooled water generally accumulates in lower areas of the field or between rows, especially if raised beds are used. The key distinction between flood water and pooled water is that flood water originates from an uncontrollable source such as a river or creek.  Standing water that originated from a river or creek would still be considered flood water. Pooled water can cause damage to crops, but is generally not considered to carry as much risk for microbial contamination as flood water. In the case of pooled water, growers should consider whether or not the water is contacting the edible portion of the crop, how long the water was pooled, previous soil amendments, and whether or not the pooled water has resulted in increased wildlife activity in or near the affected area.

Fields that have experienced flooding present growers with difficult management choices. Flooding is defined (per FDA) as the “Flowing or overflowing of a field with water outside a grower’s control”. Flooding is associated with streams, creeks, or ponds that overflow their banks and cannot be controlled. The FDA considers food contacted by flood water to be “adulterated” and not fit for human consumption. Due to microbial and other concerns, produce cannot be harvested and sold into the public food supply once it contacts flood water.

Fortunately, most crops are nowhere near harvest and many crops have yet to be planted. In those cases where flooding does occur in or near the crop but does not contact the edible portion of the crop, FDA guidance states that growers should, “Evaluate on a case-by-case basis for the likelihood of contamination”.

The following are considerations for managing flooded fields:

  1. Document the extent of any flooding in fields with photos and flags or other markers. This will insure that the flooded area remains defined once flood waters have receded. In the case of planted fields, photos will help other involved parties (ex. Insurance adjusters, third-party auditors) to understand the extent of the issue.
  2. Remember that flood water introduces more than microbial risks. Flood water may contain mycotoxins, PCB’s, heavy metals, pesticides, or other contaminants. While growers can test for any of these contaminants, tests are not definitive and there is always the chance for a “false negative”. Seek technical advice before investing in tests for non-microbial contaminants.
  3. Growers should consider planting previously flooded fields to agronomic crops for this season. If this is not possible, another strategy would be to plant previously flooded fields to crops defined by FDA as “seldom consumed raw”. These crops include pumpkins, winter squash, and sweet corn. These crops are generally cooked prior to consumption, which mitigates many microbial risks.
  4. Once flood water has receded, leave the flooded area undisturbed for as long as possible. Research done at the Southwest Purdue Ag Center in 2015 indicated that the population of microbes introduced into a field through flooding decreased most quickly when the soil was left undisturbed. Allowing undisturbed soil to thoroughly dry on the surface and maximizing exposure to sunlight appears to encourage a decrease in microbes deposited by flood water near the soil surface. Tillage, cover crop establishment, or any other operation that disturbs the soil incorporates oxygen and drives flood-deposited microbes into the soil where they may exist for an extended period of time.
  5. Check your well. Any wells affected by flooding that are used to supply agricultural or postharvest water should be tested for generic E. coli (CFU/100 ml water) prior to use.

If only part of a field is affected by flooding, growers should manage the flooded portion so that it does not affect the unflooded part. In addition to the above recommendations, growers should do the following to protect unflooded parts of a field:

  1. Define a buffer zone beyond the flooded area where produce is not planted. It is recommended that the area be at least 30 ft. wide. This will help to reduce the risk of cross contamination of splashing from overhead irrigation or additional rainfall.
  2. If at all possible, avoid traveling through the flooded areas to access the unflooded portion of the field. This helps to insure that microbes don’t hitch a ride on boots, shoes, or tires.
  3. Wear boots and gloves while working in flooded areas. Be sure to clean them thoroughly before entering the unaffected areas.
  4. Any equipment that is used in flooded areas should be thoroughly cleaned prior to entering unaffected areas. Ideally, equipment should be used in unaffected areas first, and flooded areas last.

Remember that these are general recommendations. Growers who undergo third party audits for GAPs certification should consult their particular audit scheme for specific guidance and requirements.

References:

FDA 2011. Guidance for Industry: Evaluating the Safety of Flood-affected Food Crops for Human Consumption. http://www.fda.gov/Food/GuidanceRegulation/ GuidanceDocumentsRegulatoryInformation/EmergencyResponse/ucm287808.htm [Accessed 05/03/17]

Maynard, E.T. 2010.  Good Agricultural Practices for Food Safety: Water Quality.  GAPs A-Z Curriculum Module.

Monroe, J.S., Deering, A.J., Heo, Y., Schmitz, H.F., and Clingerman, V.A. 2015. The effect of soil remediation treatments on microbial populations following an extreme flooding event. http://www.centerforproducesafety.org/amass/documents/researchproject/401/CPS%20Final%20Report%20RR_S.%20Monroe_Feb%202016.pdf [Accessed 05/03/17].

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