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Food safety and flooding fields

Annalisa Hultberg, Extension Educator, food safety

With this very wet summer, some farms in Minnesota have seen significant flooding damage. Flooding can be detrimental to crops for a number of reasons, including potentially introducing chemical and microbial risks to the fresh produce that can then cause human illness if ingested.  Here are some guidelines to keep in mind when you are considering the safety of your produce after a flooding event. 

  Image courtesy of Produce Safety Alliance and Keith McCall,
 of the National Resource Conservation Service

Food Safety Risks with Flooding

First, remember that according to the FDA, floodwater is defined as the water that has come onto your property from a source off the property. It is not just heavy rain falling and pooling around your plants, or a sprinkler left on overnight. 

The risks from flood waters that come in two main categories: 
  • human microbiological pathogens such as bacteria, viruses and parasites that can cause foodborne illness
  • chemicals, heavy metals, and petroleum products.
These biological and chemical contaminants, even if you cannot see them, cannot be safely removed from the produce via washing, and make the produce unsafe for consumption and the produce must be considered adulterated.

What do I do with produce that has been touched by flood waters?

Because of the significant risk that floodwater carries, if the edible portion of produce comes into direct contact with floodwaters it needs to be discarded. This includes root vegetables in the soil, squash and melons with a hard rind. 

For crops that are in or near flooded areas where water did not contact the edible portion of the crops, such as staked tomatoes or sweet corn, evaluate each situation and the risks. Ask, did the water splash onto the edible portion of the crop? How far above the water was it? Remember that flood water can have very high levels of heavy metals and pathogens, and even small amounts can contaminate produce. If in doubt, it is best to err on the side of caution and discard affected produce to avoid illness with your customers, and to avoid any foodborne illness that might be traced back to your farm.

Can I replant the fields in vegetables?

As for replanting or harvesting items that grow after the flood, that would be based on your own risk assessment and the extent of flooding. The FDA recommends waiting at least 30-60 days before replanting vegetables in flooded fields.  

If you think that the water that was on the field could have contained heavy metals or high levels of contaminants, ie if there was an animal operation just upstream from you, it would be best to wait to replant at least 60 days. If the water was low risk in your estimation, and the crop you are growing is off the ground with low risk of touching the soil, the soil might be lower risk. Unfortunately there is not a hard and fast rule since there are many things to consider when making that judgement. 

One good option might be to plant the field to cover crops until next growing season. For more information on planting suggestions, see this Flooding in Vegetable Fields, Iowa State University blog.

For more information on flooding and produce fields from UMN Extension, see this page.

For more information and resources on flooding in Minnesota see the Department of Agriculture here .

A few other tips: 

Flooding can impact wells, if the well head was submerged. If the well head was submerged on your property, test the well for generic E. coli, which will indicate fecal contamination. See here for more information on testing your well after flooding. 

Consider putting flags and place markers at the high-water lines on your fields so you can identify the areas where crops were in contact with flood waters. This will help you identify which produce items have come in contact with the flood waters.

Please find more information here:

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